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* epoll: use try_cmpxchg in list_add_tail_locklessUros Bizjak2022-09-121-1/+1
| | | | | | | | | | | | | | Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in list_add_tail_lockless. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). No functional change intended. Link: https://lkml.kernel.org/r/20220714173255.12987-1-ubizjak@gmail.com Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
* epoll: autoremove wakers even more aggressivelyBenjamin Segall2022-07-181-0/+22
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | If a process is killed or otherwise exits while having active network connections and many threads waiting on epoll_wait, the threads will all be woken immediately, but not removed from ep->wq. Then when network traffic scans ep->wq in wake_up, every wakeup attempt will fail, and will not remove the entries from the list. This means that the cost of the wakeup attempt is far higher than usual, does not decrease, and this also competes with the dying threads trying to actually make progress and remove themselves from the wq. Handle this by removing visited epoll wq entries unconditionally, rather than only when the wakeup succeeds - the structure of ep_poll means that the only potential loss is the timed_out->eavail heuristic, which now can race and result in a redundant ep_send_events attempt. (But only when incoming data and a timeout actually race, not on every timeout) Shakeel added: : We are seeing this issue in production with real workloads and it has : caused hard lockups. Particularly network heavy workloads with a lot : of threads in epoll_wait() can easily trigger this issue if they get : killed (oom-killed in our case). Link: https://lkml.kernel.org/r/xm26fsjotqda.fsf@google.com Signed-off-by: Ben Segall <bsegall@google.com> Tested-by: Shakeel Butt <shakeelb@google.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Shakeel Butt <shakeelb@google.com> Cc: Eric Dumazet <edumazet@google.com> Cc: Roman Penyaev <rpenyaev@suse.de> Cc: Jason Baron <jbaron@akamai.com> Cc: Khazhismel Kumykov <khazhy@google.com> Cc: Heiher <r@hev.cc> Cc: <stable@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
* eventpoll: simplify sysctl declaration with register_sysctl()Xiaoming Ni2022-01-221-1/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The kernel/sysctl.c is a kitchen sink where everyone leaves their dirty dishes, this makes it very difficult to maintain. To help with this maintenance let's start by moving sysctls to places where they actually belong. The proc sysctl maintainers do not want to know what sysctl knobs you wish to add for your own piece of code, we just care about the core logic. So move the epoll_table sysctl to fs/eventpoll.c and use register_sysctl(). Link: https://lkml.kernel.org/r/20211123202422.819032-9-mcgrof@kernel.org Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Amir Goldstein <amir73il@gmail.com> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Antti Palosaari <crope@iki.fi> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Benjamin LaHaise <bcrl@kvack.org> Cc: Clemens Ladisch <clemens@ladisch.de> Cc: David Airlie <airlied@linux.ie> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Iurii Zaikin <yzaikin@google.com> Cc: Jani Nikula <jani.nikula@linux.intel.com> Cc: Jan Kara <jack@suse.cz> Cc: Joel Becker <jlbec@evilplan.org> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Joseph Qi <joseph.qi@linux.alibaba.com> Cc: Julia Lawall <julia.lawall@inria.fr> Cc: Kees Cook <keescook@chromium.org> Cc: Lukas Middendorf <kernel@tuxforce.de> Cc: Mark Fasheh <mark@fasheh.com> Cc: Paul Turner <pjt@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Petr Mladek <pmladek@suse.com> Cc: Phillip Potter <phil@philpotter.co.uk> Cc: Qing Wang <wangqing@vivo.com> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com> Cc: Sebastian Reichel <sre@kernel.org> Cc: Sergey Senozhatsky <senozhatsky@chromium.org> Cc: Stephen Kitt <steve@sk2.org> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: Douglas Gilbert <dgilbert@interlog.com> Cc: James E.J. Bottomley <jejb@linux.ibm.com> Cc: Jani Nikula <jani.nikula@intel.com> Cc: John Ogness <john.ogness@linutronix.de> Cc: Martin K. Petersen <martin.petersen@oracle.com> Cc: "Rafael J. Wysocki" <rafael@kernel.org> Cc: Steven Rostedt (VMware) <rostedt@goodmis.org> Cc: Suren Baghdasaryan <surenb@google.com> Cc: "Theodore Ts'o" <tytso@mit.edu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* Merge tag 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-armLinus Torvalds2021-09-091-3/+2
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Pull ARM development updates from Russell King: - Rename "mod_init" and "mod_exit" so that initcall debug output is actually useful (Randy Dunlap) - Update maintainers entries for linux-arm-kernel to indicate it is moderated for non-subscribers (Randy Dunlap) - Move install rules to arch/arm/Makefile (Masahiro Yamada) - Drop unnecessary ARCH_NR_GPIOS definition (Linus Walleij) - Don't warn about atags_to_fdt() stack size (David Heidelberg) - Speed up unaligned copy_{from,to}_kernel_nofault (Arnd Bergmann) - Get rid of set_fs() usage (Arnd Bergmann) - Remove checks for GCC prior to v4.6 (Geert Uytterhoeven) * tag 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-arm: ARM: 9118/1: div64: Remove always-true __div64_const32_is_OK() duplicate ARM: 9117/1: asm-generic: div64: Remove always-true __div64_const32_is_OK() ARM: 9116/1: unified: Remove check for gcc < 4 ARM: 9110/1: oabi-compat: fix oabi epoll sparse warning ARM: 9113/1: uaccess: remove set_fs() implementation ARM: 9112/1: uaccess: add __{get,put}_kernel_nofault ARM: 9111/1: oabi-compat: rework fcntl64() emulation ARM: 9114/1: oabi-compat: rework sys_semtimedop emulation ARM: 9108/1: oabi-compat: rework epoll_wait/epoll_pwait emulation ARM: 9107/1: syscall: always store thread_info->abi_syscall ARM: 9109/1: oabi-compat: add epoll_pwait handler ARM: 9106/1: traps: use get_kernel_nofault instead of set_fs() ARM: 9115/1: mm/maccess: fix unaligned copy_{from,to}_kernel_nofault ARM: 9105/1: atags_to_fdt: don't warn about stack size ARM: 9103/1: Drop ARCH_NR_GPIOS definition ARM: 9102/1: move theinstall rules to arch/arm/Makefile ARM: 9100/1: MAINTAINERS: mark all linux-arm-kernel@infradead list as moderated ARM: 9099/1: crypto: rename 'mod_init' & 'mod_exit' functions to be module-specific
| * ARM: 9108/1: oabi-compat: rework epoll_wait/epoll_pwait emulationArnd Bergmann2021-08-201-3/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The epoll_wait() system call wrapper is one of the remaining users of the set_fs() infrasturcture for Arm. Changing it to not require set_fs() is rather complex unfortunately. The approach I'm taking here is to allow architectures to override the code that copies the output to user space, and let the oabi-compat implementation check whether it is getting called from an EABI or OABI system call based on the thread_info->syscall value. The in_oabi_syscall() check here mirrors the in_compat_syscall() and in_x32_syscall() helpers for 32-bit compat implementations on other architectures. Overall, the amount of code goes down, at least with the newly added sys_oabi_epoll_pwait() helper getting removed again. The downside is added complexity in the source code for the native implementation. There should be no difference in runtime performance except for Arm kernels with CONFIG_OABI_COMPAT enabled that now have to go through an external function call to check which of the two variants to use. Acked-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
* | fs/epoll: use a per-cpu counter for user's watches countNicholas Piggin2021-09-081-8/+10
|/ | | | | | | | | | | | | | | | | | | | | This counter tracks the number of watches a user has, to compare against the 'max_user_watches' limit. This causes a scalability bottleneck on SPECjbb2015 on large systems as there is only one user. Changing to a per-cpu counter increases throughput of the benchmark by about 30% on a 16-socket, > 1000 thread system. [rdunlap@infradead.org: fix build errors in kernel/user.c when CONFIG_EPOLL=n] [npiggin@gmail.com: move ifdefs into wrapper functions, slightly improve panic message] Link: https://lkml.kernel.org/r/1628051945.fens3r99ox.astroid@bobo.none [akpm@linux-foundation.org: tweak user_epoll_alloc(), per Guenter] Link: https://lkml.kernel.org/r/20210804191421.GA1900577@roeck-us.net Link: https://lkml.kernel.org/r/20210802032013.2751916-1-npiggin@gmail.com Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Reported-by: Anton Blanchard <anton@ozlabs.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* fs/epoll: restore waking from ep_done_scan()Davidlohr Bueso2021-05-071-0/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | Commit 339ddb53d373 ("fs/epoll: remove unnecessary wakeups of nested epoll") changed the userspace visible behavior of exclusive waiters blocked on a common epoll descriptor upon a single event becoming ready. Previously, all tasks doing epoll_wait would awake, and now only one is awoken, potentially causing missed wakeups on applications that rely on this behavior, such as Apache Qpid. While the aforementioned commit aims at having only a wakeup single path in ep_poll_callback (with the exceptions of epoll_ctl cases), we need to restore the wakeup in what was the old ep_scan_ready_list() such that the next thread can be awoken, in a cascading style, after the waker's corresponding ep_send_events(). Link: https://lkml.kernel.org/r/20210405231025.33829-3-dave@stgolabs.net Fixes: 339ddb53d373 ("fs/epoll: remove unnecessary wakeups of nested epoll") Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Jason Baron <jbaron@akamai.com> Cc: Roman Penyaev <rpenyaev@suse.de> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* fs: eventpoll: fix comments & kernel-doc notationRandy Dunlap2021-03-071-26/+26
| | | | | | | | | | | | | | | | | | | | | | Use the documented kernel-doc format for function Return: descriptions. Begin constant values in kernel-doc comments with '%'. Remove kernel-doc "/**" from 2 functions that are not documented with kernel-doc notation. Fix typos, punctuation, & grammar. Also fix a few kernel-doc warnings: ../fs/eventpoll.c:1883: warning: Function parameter or member 'ep' not described in 'ep_loop_check_proc' ../fs/eventpoll.c:1883: warning: Excess function parameter 'priv' description in 'ep_loop_check_proc' ../fs/eventpoll.c:1932: warning: Function parameter or member 'ep' not described in 'ep_loop_check' ../fs/eventpoll.c:1932: warning: Excess function parameter 'from' description in 'ep_loop_check' Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
* kcmp: Support selection of SYS_kcmp without CHECKPOINT_RESTOREChris Wilson2021-02-161-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Userspace has discovered the functionality offered by SYS_kcmp and has started to depend upon it. In particular, Mesa uses SYS_kcmp for os_same_file_description() in order to identify when two fd (e.g. device or dmabuf) point to the same struct file. Since they depend on it for core functionality, lift SYS_kcmp out of the non-default CONFIG_CHECKPOINT_RESTORE into the selectable syscall category. Rasmus Villemoes also pointed out that systemd uses SYS_kcmp to deduplicate the per-service file descriptor store. Note that some distributions such as Ubuntu are already enabling CHECKPOINT_RESTORE in their configs and so, by extension, SYS_kcmp. References: https://gitlab.freedesktop.org/drm/intel/-/issues/3046 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Kees Cook <keescook@chromium.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Will Drewry <wad@chromium.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Dave Airlie <airlied@gmail.com> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: Lucas Stach <l.stach@pengutronix.de> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk> Cc: Cyrill Gorcunov <gorcunov@gmail.com> Cc: stable@vger.kernel.org Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> # DRM depends on kcmp Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> # systemd uses kcmp Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com> Reviewed-by: Kees Cook <keescook@chromium.org> Acked-by: Thomas Zimmermann <tzimmermann@suse.de> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/20210205220012.1983-1-chris@chris-wilson.co.uk
* epoll: add syscall epoll_pwait2Willem de Bruijn2020-12-191-14/+73
| | | | | | | | | | | | | | | | | | | | | | | | | | | Add syscall epoll_pwait2, an epoll_wait variant with nsec resolution that replaces int timeout with struct timespec. It is equivalent otherwise. int epoll_pwait2(int fd, struct epoll_event *events, int maxevents, const struct timespec *timeout, const sigset_t *sigset); The underlying hrtimer is already programmed with nsec resolution. pselect and ppoll also set nsec resolution timeout with timespec. The sigset_t in epoll_pwait has a compat variant. epoll_pwait2 needs the same. For timespec, only support this new interface on 2038 aware platforms that define __kernel_timespec_t. So no CONFIG_COMPAT_32BIT_TIME. Link: https://lkml.kernel.org/r/20201121144401.3727659-3-willemdebruijn.kernel@gmail.com Signed-off-by: Willem de Bruijn <willemb@google.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* epoll: convert internal api to timespec64Willem de Bruijn2020-12-191-20/+37
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Patch series "add epoll_pwait2 syscall", v4. Enable nanosecond timeouts for epoll. Analogous to pselect and ppoll, introduce an epoll_wait syscall variant that takes a struct timespec instead of int timeout. This patch (of 4): Make epoll more consistent with select/poll: pass along the timeout as timespec64 pointer. In anticipation of additional changes affecting all three polling mechanisms: - add epoll_pwait2 syscall with timespec semantics, and share poll_select_set_timeout implementation. - compute slack before conversion to absolute time, to save one ktime_get_ts64 call. Link: https://lkml.kernel.org/r/20201121144401.3727659-1-willemdebruijn.kernel@gmail.com Link: https://lkml.kernel.org/r/20201121144401.3727659-2-willemdebruijn.kernel@gmail.com Signed-off-by: Willem de Bruijn <willemb@google.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* epoll: eliminate unnecessary lock for zero timeoutSoheil Hassas Yeganeh2020-12-191-13/+12
| | | | | | | | | | | | | | | | | | | | | | | | | | We call ep_events_available() under lock when timeout is 0, and then call it without locks in the loop for the other cases. Instead, call ep_events_available() without lock for all cases. For non-zero timeouts, we will recheck after adding the thread to the wait queue. For zero timeout cases, by definition, user is opportunistically polling and will have to call epoll_wait again in the future. Note that this lock was kept in c5a282e9635e9 because the whole loop was historically under lock. This patch results in a 1% CPU/RPC reduction in RPC benchmarks. Link: https://lkml.kernel.org/r/20201106231635.3528496-9-soheil.kdev@gmail.com Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com> Suggested-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Willem de Bruijn <willemb@google.com> Reviewed-by: Khazhismel Kumykov <khazhy@google.com> Cc: Guantao Liu <guantaol@google.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* epoll: replace gotos with a proper loopSoheil Hassas Yeganeh2020-12-191-21/+21
| | | | | | | | | | | | | | | | | | The existing loop is pointless, and the labels make it really hard to follow the structure. Replace that control structure with a simple loop that returns when there are new events, there is a signal, or the thread has timed out. Link: https://lkml.kernel.org/r/20201106231635.3528496-8-soheil.kdev@gmail.com Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Willem de Bruijn <willemb@google.com> Reviewed-by: Khazhismel Kumykov <khazhy@google.com> Cc: Guantao Liu <guantaol@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* epoll: pull all code between fetch_events and send_event into the loopSoheil Hassas Yeganeh2020-12-191-20/+21
| | | | | | | | | | | | | | This is a no-op change which simplifies the follow up patches. Link: https://lkml.kernel.org/r/20201106231635.3528496-7-soheil.kdev@gmail.com Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Willem de Bruijn <willemb@google.com> Reviewed-by: Khazhismel Kumykov <khazhy@google.com> Cc: Guantao Liu <guantaol@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* epoll: simplify and optimize busy loop logicSoheil Hassas Yeganeh2020-12-191-23/+17
| | | | | | | | | | | | | | | | | | | | | ep_events_available() is called multiple times around the busy loop logic, even though the logic is generally not used. ep_reset_busy_poll_napi_id() is similarly always called, even when busy loop is not used. Eliminate ep_reset_busy_poll_napi_id() and inline it inside ep_busy_loop(). Make ep_busy_loop() return whether there are any events available after the busy loop. This will eliminate unnecessary loads and branches, and simplifies the loop. Link: https://lkml.kernel.org/r/20201106231635.3528496-6-soheil.kdev@gmail.com Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Willem de Bruijn <willemb@google.com> Reviewed-by: Khazhismel Kumykov <khazhy@google.com> Cc: Guantao Liu <guantaol@google.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* epoll: move eavail next to the list_empty_careful checkSoheil Hassas Yeganeh2020-12-191-2/+1
| | | | | | | | | | | | | | This is a no-op change and simply to make the code more coherent. Link: https://lkml.kernel.org/r/20201106231635.3528496-5-soheil.kdev@gmail.com Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Willem de Bruijn <willemb@google.com> Reviewed-by: Khazhismel Kumykov <khazhy@google.com> Cc: Guantao Liu <guantaol@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* epoll: pull fatal signal checks into ep_send_events()Soheil Hassas Yeganeh2020-12-191-9/+8
| | | | | | | | | | | | | | | | | | | | | To simplify the code, pull in checking the fatal signals into ep_send_events(). ep_send_events() is called only from ep_poll(). Note that, previously, we were always checking fatal events, but it is checked only if eavail is true. This should be fine because the goal of that check is to quickly return from epoll_wait() when there is a pending fatal signal. Link: https://lkml.kernel.org/r/20201106231635.3528496-4-soheil.kdev@gmail.com Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com> Suggested-by: Willem de Bruijn <willemb@google.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Willem de Bruijn <willemb@google.com> Reviewed-by: Khazhismel Kumykov <khazhy@google.com> Cc: Guantao Liu <guantaol@google.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* epoll: simplify signal handlingSoheil Hassas Yeganeh2020-12-191-10/+10
| | | | | | | | | | | | | | | | | | Check signals before locking ep->lock, and immediately return -EINTR if there is any signal pending. This saves a few loads, stores, and branches from the hot path and simplifies the loop structure for follow up patches. Link: https://lkml.kernel.org/r/20201106231635.3528496-3-soheil.kdev@gmail.com Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Willem de Bruijn <willemb@google.com> Reviewed-by: Khazhismel Kumykov <khazhy@google.com> Cc: Guantao Liu <guantaol@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* epoll: check for events when removing a timed out thread from the wait queueSoheil Hassas Yeganeh2020-12-191-9/+16
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Patch series "simplify ep_poll". This patch series is a followup based on the suggestions and feedback by Linus: https://lkml.kernel.org/r/CAHk-=wizk=OxUyQPbO8MS41w2Pag1kniUV5WdD5qWL-gq1kjDA@mail.gmail.com The first patch in the series is a fix for the epoll race in presence of timeouts, so that it can be cleanly backported to all affected stable kernels. The rest of the patch series simplify the ep_poll() implementation. Some of these simplifications result in minor performance enhancements as well. We have kept these changes under self tests and internal benchmarks for a few days, and there are minor (1-2%) performance enhancements as a result. This patch (of 8): After abc610e01c66 ("fs/epoll: avoid barrier after an epoll_wait(2) timeout"), we break out of the ep_poll loop upon timeout, without checking whether there is any new events available. Prior to that patch-series we always called ep_events_available() after exiting the loop. This can cause races and missed wakeups. For example, consider the following scenario reported by Guantao Liu: Suppose we have an eventfd added using EPOLLET to an epollfd. Thread 1: Sleeps for just below 5ms and then writes to an eventfd. Thread 2: Calls epoll_wait with a timeout of 5 ms. If it sees an event of the eventfd, it will write back on that fd. Thread 3: Calls epoll_wait with a negative timeout. Prior to abc610e01c66, it is guaranteed that Thread 3 will wake up either by Thread 1 or Thread 2. After abc610e01c66, Thread 3 can be blocked indefinitely if Thread 2 sees a timeout right before the write to the eventfd by Thread 1. Thread 2 will be woken up from schedule_hrtimeout_range and, with evail 0, it will not call ep_send_events(). To fix this issue: 1) Simplify the timed_out case as suggested by Linus. 2) while holding the lock, recheck whether the thread was woken up after its time out has reached. Note that (2) is different from Linus' original suggestion: It do not set "eavail = ep_events_available(ep)" to avoid unnecessary contention (when there are too many timed-out threads and a small number of events), as well as races mentioned in the discussion thread. This is the first patch in the series so that the backport to stable releases is straightforward. Link: https://lkml.kernel.org/r/20201106231635.3528496-1-soheil.kdev@gmail.com Link: https://lkml.kernel.org/r/CAHk-=wizk=OxUyQPbO8MS41w2Pag1kniUV5WdD5qWL-gq1kjDA@mail.gmail.com Link: https://lkml.kernel.org/r/20201106231635.3528496-2-soheil.kdev@gmail.com Fixes: abc610e01c66 ("fs/epoll: avoid barrier after an epoll_wait(2) timeout") Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com> Tested-by: Guantao Liu <guantaol@google.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Reported-by: Guantao Liu <guantaol@google.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Willem de Bruijn <willemb@google.com> Reviewed-by: Khazhismel Kumykov <khazhy@google.com> Reviewed-by: Davidlohr Bueso <dbueso@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* Merge branch 'work.epoll' of ↵Linus Torvalds2020-12-161-415/+302
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs Pull epoll updates from Al Viro: "Deal with epoll loop check/removal races sanely (among other things). The solution merged last cycle (pinning a bunch of struct file instances) had been forced by the wrong data structures; untangling that takes a bunch of preparations, but it's worth doing - control flow in there is ridiculously overcomplicated. Memory footprint has also gone down, while we are at it. This is not all I want to do in the area, but since I didn't get around to posting the followups they'll have to wait for the next cycle" * 'work.epoll' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (27 commits) epoll: take epitem list out of struct file epoll: massage the check list insertion lift rcu_read_lock() into reverse_path_check() convert ->f_ep_links/->fllink to hlist ep_insert(): move creation of wakeup source past the fl_ep_links insertion fold ep_read_events_proc() into the only caller take the common part of ep_eventpoll_poll() and ep_item_poll() into helper ep_insert(): we only need tep->mtx around the insertion itself ep_insert(): don't open-code ep_remove() on failure exits lift locking/unlocking ep->mtx out of ep_{start,done}_scan() ep_send_events_proc(): fold into the caller lift the calls of ep_send_events_proc() into the callers lift the calls of ep_read_events_proc() into the callers ep_scan_ready_list(): prepare to splitup ep_loop_check_proc(): saner calling conventions get rid of ep_push_nested() ep_loop_check_proc(): lift pushing the cookie into callers clean reverse_path_check_proc() a bit reverse_path_check_proc(): don't bother with cookies reverse_path_check_proc(): sane arguments ...
| * epoll: take epitem list out of struct fileAl Viro2020-10-261-42/+126
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Move the head of epitem list out of struct file; for epoll ones it's moved into struct eventpoll (->refs there), for non-epoll - into the new object (struct epitem_head). In place of ->f_ep_links we leave a pointer to the list head (->f_ep). ->f_ep is protected by ->f_lock and it's zeroed as soon as the list of epitems becomes empty (that can happen only in ep_remove() by now). The list of files for reverse path check is *not* going through struct file now - it's a single-linked list going through epitem_head instances. It's terminated by ERR_PTR(-1) (== EP_UNACTIVE_POINTER), so the elements of list can be distinguished by head->next != NULL. epitem_head instances are allocated at ep_insert() time (by attach_epitem()) and freed either by ep_remove() (if it empties the set of epitems *and* epitem_head does not belong to the reverse path check list) or by clear_tfile_check_list() when the list is emptied (if the set of epitems is empty by that point). Allocations are done from a separate slab - minimal kmalloc() size is too large on some architectures. As the result, we trim struct file _and_ get rid of the games with temporary file references. Locking and barriers are interesting (aren't they always); see unlist_file() and ep_remove() for details. The non-obvious part is that ep_remove() needs to decide if it will be the one to free the damn thing *before* actually storing NULL to head->epitems.first - that's what smp_load_acquire is for in there. unlist_file() lockless path is safe, since we hit it only if we observe NULL in head->epitems.first and whoever had done that store is guaranteed to have observed non-NULL in head->next. IOW, their last access had been the store of NULL into ->epitems.first and we can safely free the sucker. OTOH, we are under rcu_read_lock() and both epitem and epitem->file have their freeing RCU-delayed. So if we see non-NULL ->epitems.first, we can grab ->f_lock (all epitems in there share the same struct file) and safely recheck the emptiness of ->epitems; again, ->next is still non-NULL, so ep_remove() couldn't have freed head yet. ->f_lock serializes us wrt ep_remove(); the rest is trivial. Note that once head->epitems becomes NULL, nothing can get inserted into it - the only remaining reference to head after that point is from the reverse path check list. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * epoll: massage the check list insertionAl Viro2020-10-261-4/+4
| | | | | | | | | | | | | | | | in the "non-epoll target" cases do it in ep_insert() rather than in do_epoll_ctl(), so that we do it only with some epitem is already guaranteed to exist. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * lift rcu_read_lock() into reverse_path_check()Al Viro2020-10-261-2/+2
| | | | | | | | Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * convert ->f_ep_links/->fllink to hlistAl Viro2020-10-261-9/+9
| | | | | | | | | | | | we don't care about the order of elements there Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * ep_insert(): move creation of wakeup source past the fl_ep_links insertionAl Viro2020-10-261-11/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | | | That's the beginning of preparations for taking f_ep_links out of struct file. If insertion might fail, we will need a new failure exit. Having wakeup source creation done after that point will simplify life there; ep_remove() can (and commonly does) live with NULL epi->ws, so it can be used for cleanup after ep_create_wakeup_source() failure. It can't be used before the rbtree insertion, though, so if we are to unify all old failure exits, we need to move that thing down. Then we would be free to do simple kmem_cache_free() on the failure to insert into f_ep_links - no wakeup source to leak on that failure exit. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * fold ep_read_events_proc() into the only callerAl Viro2020-10-261-29/+20
| | | | | | | | Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * take the common part of ep_eventpoll_poll() and ep_item_poll() into helperAl Viro2020-10-261-30/+27
| | | | | | | | | | | | | | | | | | | | The only reason why ep_item_poll() can't simply call ep_eventpoll_poll() (or, better yet, call vfs_poll() in all cases) is that we need to tell lockdep how deep into the hierarchy of ->mtx we are. So let's add a variant of ep_eventpoll_poll() that would take depth explicitly and turn ep_eventpoll_poll() into wrapper for that. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * ep_insert(): we only need tep->mtx around the insertion itselfAl Viro2020-10-261-18/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | We do need ep->mtx (and we are holding it all along), but that's the lock on the epoll we are inserting into; locking of the epoll being inserted is not needed for most of that work - as the matter of fact, we only need it to provide barriers for the fastpath check (for now). Move taking and releasing it into ep_insert(). The caller (do_epoll_ctl()) doesn't need to bother with that at all. Moreover, that way we kill the kludge in ep_item_poll() - now it's always called with tep unlocked. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * ep_insert(): don't open-code ep_remove() on failure exitsAl Viro2020-10-261-37/+14
| | | | | | | | Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * lift locking/unlocking ep->mtx out of ep_{start,done}_scan()Al Viro2020-10-261-31/+26
| | | | | | | | | | | | | | | | get rid of depth/ep_locked arguments there and document the kludge in ep_item_poll() that has lead to ep_locked existence in the first place Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * ep_send_events_proc(): fold into the callerAl Viro2020-10-261-40/+20
| | | | | | | | | | | | | | | | | | ... and get rid of struct ep_send_events_data - not needed anymore. The weird way of passing the arguments in (and real return value out - nominal return value of ep_send_events_proc() is ignored) was due to the signature forced on ep_scan_ready_list() callbacks. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * lift the calls of ep_send_events_proc() into the callersAl Viro2020-10-261-28/+5
| | | | | | | | | | | | ... and kill ep_scan_ready_list() Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * lift the calls of ep_read_events_proc() into the callersAl Viro2020-10-261-10/+14
| | | | | | | | | | | | | | | | | | Expand the calls of ep_scan_ready_list() that get ep_read_events_proc(). As a side benefit we can pass depth to ep_read_events_proc() by value and not by address - the latter used to be forced by the signature expected from ep_scan_ready_list() callback. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * ep_scan_ready_list(): prepare to splitupAl Viro2020-10-261-27/+36
| | | | | | | | | | | | take the stuff done before and after the callback into separate helpers Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * ep_loop_check_proc(): saner calling conventionsAl Viro2020-10-261-22/+16
| | | | | | | | | | | | | | | | 1) 'cookie' argument is unused; kill it. 2) 'priv' one is always an epoll struct file, and we only care about its associated struct eventpoll; pass that instead. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * get rid of ep_push_nested()Al Viro2020-10-261-25/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | The only remaining user is loop checking. But there we only need to check that we have not walked into the epoll we are inserting into - we are adding an edge to acyclic graph, so any loop being created will have to pass through the source of that edge. So we don't need that array of cookies - we have only one eventpoll to watch out for. RIP ep_push_nested(), along with the cookies array. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * ep_loop_check_proc(): lift pushing the cookie into callersAl Viro2020-10-261-6/+12
| | | | | | | | Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * clean reverse_path_check_proc() a bitAl Viro2020-10-261-17/+9
| | | | | | | | Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * reverse_path_check_proc(): don't bother with cookiesAl Viro2020-10-261-2/+1
| | | | | | | | | | | | | | We know there's no loops by the time we call it; the only thing we care about is too deep reverse paths. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * reverse_path_check_proc(): sane argumentsAl Viro2020-10-261-7/+5
| | | | | | | | | | | | | | no need to force its calling conventions to match the callback for late unlamented ep_call_nested()... Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * untangling ep_call_nested(): and there was much rejoicingAl Viro2020-10-261-32/+11
| | | | | | | | Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * untangling ep_call_nested(): move push/pop of cookie into the callbacksAl Viro2020-10-261-9/+9
| | | | | | | | Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * untangling ep_call_nested(): take pushing cookie into a helperAl Viro2020-10-261-9/+17
| | | | | | | | Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * untangling ep_call_nested(): it's all serialized on epmutex.Al Viro2020-10-261-69/+11
| | | | | | | | | | | | | | | | | | | | | | IOW, * no locking is needed to protect the list * the list is actually a stack * no need to check ->ctx * it can bloody well be a static 5-element array - nobody is going to be accessing it in parallel. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * untangling ep_call_nested(): get rid of useless argumentsAl Viro2020-10-261-19/+12
| | | | | | | | | | | | ctx is always equal to current, ncalls - to &poll_loop_ncalls. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * epoll: get rid of epitem->nwaitAl Viro2020-10-261-26/+20
| | | | | | | | | | | | | | | | we use it only to indicate allocation failures within queueing callback back to ep_insert(). Might as well use epq.epi for that reporting... Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
| * epoll: switch epitem->pwqlist to single-linked listAl Viro2020-10-261-26/+25
| | | | | | | | | | | | | | We only traverse it once to destroy all associated eppoll_entry at epitem destruction time. The order of traversal is irrelevant there. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* | net: Remove the err argument from sock_from_fileFlorent Revest2020-12-041-2/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, the sock_from_file prototype takes an "err" pointer that is either not set or set to -ENOTSOCK IFF the returned socket is NULL. This makes the error redundant and it is ignored by a few callers. This patch simplifies the API by letting callers deduce the error based on whether the returned socket is NULL or not. Suggested-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Florent Revest <revest@google.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: KP Singh <kpsingh@google.com> Link: https://lore.kernel.org/bpf/20201204113609.1850150-1-revest@google.com
* | net: Add SO_BUSY_POLL_BUDGET socket optionBjörn Töpel2020-12-011-1/+2
| | | | | | | | | | | | | | | | | | | | This option lets a user set a per socket NAPI budget for busy-polling. If the options is not set, it will use the default of 8. Signed-off-by: Björn Töpel <bjorn.topel@intel.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: Jakub Kicinski <kuba@kernel.org> Link: https://lore.kernel.org/bpf/20201130185205.196029-3-bjorn.topel@gmail.com
* | net: Introduce preferred busy-pollingBjörn Töpel2020-12-011-1/+1
|/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The existing busy-polling mode, enabled by the SO_BUSY_POLL socket option or system-wide using the /proc/sys/net/core/busy_read knob, is an opportunistic. That means that if the NAPI context is not scheduled, it will poll it. If, after busy-polling, the budget is exceeded the busy-polling logic will schedule the NAPI onto the regular softirq handling. One implication of the behavior above is that a busy/heavy loaded NAPI context will never enter/allow for busy-polling. Some applications prefer that most NAPI processing would be done by busy-polling. This series adds a new socket option, SO_PREFER_BUSY_POLL, that works in concert with the napi_defer_hard_irqs and gro_flush_timeout knobs. The napi_defer_hard_irqs and gro_flush_timeout knobs were introduced in commit 6f8b12d661d0 ("net: napi: add hard irqs deferral feature"), and allows for a user to defer interrupts to be enabled and instead schedule the NAPI context from a watchdog timer. When a user enables the SO_PREFER_BUSY_POLL, again with the other knobs enabled, and the NAPI context is being processed by a softirq, the softirq NAPI processing will exit early to allow the busy-polling to be performed. If the application stops performing busy-polling via a system call, the watchdog timer defined by gro_flush_timeout will timeout, and regular softirq handling will resume. In summary; Heavy traffic applications that prefer busy-polling over softirq processing should use this option. Example usage: $ echo 2 | sudo tee /sys/class/net/ens785f1/napi_defer_hard_irqs $ echo 200000 | sudo tee /sys/class/net/ens785f1/gro_flush_timeout Note that the timeout should be larger than the userspace processing window, otherwise the watchdog will timeout and fall back to regular softirq processing. Enable the SO_BUSY_POLL/SO_PREFER_BUSY_POLL options on your socket. Signed-off-by: Björn Töpel <bjorn.topel@intel.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: Jakub Kicinski <kuba@kernel.org> Link: https://lore.kernel.org/bpf/20201130185205.196029-2-bjorn.topel@gmail.com
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