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Commit e679654a704e ("bpf: Fix a rcu_sched stall issue with
bpf task/task_file iterator") tries to fix rcu stalls warning
which is caused by bpf task_file iterator when running
"bpftool prog".
rcu: INFO: rcu_sched self-detected stall on CPU
rcu: \x097-....: (20999 ticks this GP) idle=302/1/0x4000000000000000 softirq=1508852/1508852 fqs=4913
\x09(t=21031 jiffies g=2534773 q=179750)
NMI backtrace for cpu 7
CPU: 7 PID: 184195 Comm: bpftool Kdump: loaded Tainted: G W 5.8.0-00004-g68bfc7f8c1b4 #6
Hardware name: Quanta Twin Lakes MP/Twin Lakes Passive MP, BIOS F09_3A17 05/03/2019
Call Trace:
<IRQ>
dump_stack+0x57/0x70
nmi_cpu_backtrace.cold+0x14/0x53
? lapic_can_unplug_cpu.cold+0x39/0x39
nmi_trigger_cpumask_backtrace+0xb7/0xc7
rcu_dump_cpu_stacks+0xa2/0xd0
rcu_sched_clock_irq.cold+0x1ff/0x3d9
? tick_nohz_handler+0x100/0x100
update_process_times+0x5b/0x90
tick_sched_timer+0x5e/0xf0
__hrtimer_run_queues+0x12a/0x2a0
hrtimer_interrupt+0x10e/0x280
__sysvec_apic_timer_interrupt+0x51/0xe0
asm_call_on_stack+0xf/0x20
</IRQ>
sysvec_apic_timer_interrupt+0x6f/0x80
...
task_file_seq_next+0x52/0xa0
bpf_seq_read+0xb9/0x320
vfs_read+0x9d/0x180
ksys_read+0x5f/0xe0
do_syscall_64+0x38/0x60
entry_SYSCALL_64_after_hwframe+0x44/0xa9
The fix is to limit the number of bpf program runs to be
one million. This fixed the program in most cases. But
we also found under heavy load, which can increase the wallclock
time for bpf_seq_read(), the warning may still be possible.
For example, calling bpf_delay() in the "while" loop of
bpf_seq_read(), which will introduce artificial delay,
the warning will show up in my qemu run.
static unsigned q;
volatile unsigned *p = &q;
volatile unsigned long long ll;
static void bpf_delay(void)
{
int i, j;
for (i = 0; i < 10000; i++)
for (j = 0; j < 10000; j++)
ll += *p;
}
There are two ways to fix this issue. One is to reduce the above
one million threshold to say 100,000 and hopefully rcu warning will
not show up any more. Another is to introduce a target feature
which enables bpf_seq_read() calling cond_resched().
This patch took second approach as the first approach may cause
more -EAGAIN failures for read() syscalls. Note that not all bpf_iter
targets can permit cond_resched() in bpf_seq_read() as some, e.g.,
netlink seq iterator, rcu read lock critical section spans through
seq_ops->next() -> seq_ops->show() -> seq_ops->next().
For the kernel code with the above hack, "bpftool p" roughly takes
38 seconds to finish on my VM with 184 bpf program runs.
Using the following command, I am able to collect the number of
context switches:
perf stat -e context-switches -- ./bpftool p >& log
Without this patch,
69 context-switches
With this patch,
75 context-switches
This patch added additional 6 context switches, roughly every 6 seconds
to reschedule, to avoid lengthy no-rescheduling which may cause the
above RCU warnings.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20201028061054.1411116-1-yhs@fb.com
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git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
Pull networking fixes from Jakub Kicinski:
"Cross-tree/merge window issues:
- rtl8150: don't incorrectly assign random MAC addresses; fix late in
the 5.9 cycle started depending on a return code from a function
which changed with the 5.10 PR from the usb subsystem
Current release regressions:
- Revert "virtio-net: ethtool configurable RXCSUM", it was causing
crashes at probe when control vq was not negotiated/available
Previous release regressions:
- ixgbe: fix probing of multi-port 10 Gigabit Intel NICs with an MDIO
bus, only first device would be probed correctly
- nexthop: Fix performance regression in nexthop deletion by
effectively switching from recently added synchronize_rcu() to
synchronize_rcu_expedited()
- netsec: ignore 'phy-mode' device property on ACPI systems; the
property is not populated correctly by the firmware, but firmware
configures the PHY so just keep boot settings
Previous releases - always broken:
- tcp: fix to update snd_wl1 in bulk receiver fast path, addressing
bulk transfers getting "stuck"
- icmp: randomize the global rate limiter to prevent attackers from
getting useful signal
- r8169: fix operation under forced interrupt threading, make the
driver always use hard irqs, even on RT, given the handler is light
and only wants to schedule napi (and do so through a _irqoff()
variant, preferably)
- bpf: Enforce pointer id generation for all may-be-null register
type to avoid pointers erroneously getting marked as null-checked
- tipc: re-configure queue limit for broadcast link
- net/sched: act_tunnel_key: fix OOB write in case of IPv6 ERSPAN
tunnels
- fix various issues in chelsio inline tls driver
Misc:
- bpf: improve just-added bpf_redirect_neigh() helper api to support
supplying nexthop by the caller - in case BPF program has already
done a lookup we can avoid doing another one
- remove unnecessary break statements
- make MCTCP not select IPV6, but rather depend on it"
* tag 'net-5.10-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net: (62 commits)
tcp: fix to update snd_wl1 in bulk receiver fast path
net: Properly typecast int values to set sk_max_pacing_rate
netfilter: nf_fwd_netdev: clear timestamp in forwarding path
ibmvnic: save changed mac address to adapter->mac_addr
selftests: mptcp: depends on built-in IPv6
Revert "virtio-net: ethtool configurable RXCSUM"
rtnetlink: fix data overflow in rtnl_calcit()
net: ethernet: mtk-star-emac: select REGMAP_MMIO
net: hdlc_raw_eth: Clear the IFF_TX_SKB_SHARING flag after calling ether_setup
net: hdlc: In hdlc_rcv, check to make sure dev is an HDLC device
bpf, libbpf: Guard bpf inline asm from bpf_tail_call_static
bpf, selftests: Extend test_tc_redirect to use modified bpf_redirect_neigh()
bpf: Fix bpf_redirect_neigh helper api to support supplying nexthop
mptcp: depends on IPV6 but not as a module
sfc: move initialisation of efx->filter_sem to efx_init_struct()
mpls: load mpls_gso after mpls_iptunnel
net/sched: act_tunnel_key: fix OOB write in case of IPv6 ERSPAN tunnels
net/sched: act_gate: Unlock ->tcfa_lock in tc_setup_flow_action()
net: dsa: bcm_sf2: make const array static, makes object smaller
mptcp: MPTCP_IPV6 should depend on IPV6 instead of selecting it
...
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The commit af7ec1383361 ("bpf: Add bpf_skc_to_tcp6_sock() helper")
introduces RET_PTR_TO_BTF_ID_OR_NULL and
the commit eaa6bcb71ef6 ("bpf: Introduce bpf_per_cpu_ptr()")
introduces RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL.
Note that for RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL, the reg0->type
could become PTR_TO_MEM_OR_NULL which is not covered by
BPF_PROBE_MEM.
The BPF_REG_0 will then hold a _OR_NULL pointer type. This _OR_NULL
pointer type requires the bpf program to explicitly do a NULL check first.
After NULL check, the verifier will mark all registers having
the same reg->id as safe to use. However, the reg->id
is not set for those new _OR_NULL return types. One of the ways
that may be wrong is, checking NULL for one btf_id typed pointer will
end up validating all other btf_id typed pointers because
all of them have id == 0. The later tests will exercise
this path.
To fix it and also avoid similar issue in the future, this patch
moves the id generation logic out of each individual RET type
test in check_helper_call(). Instead, it does one
reg_type_may_be_null() test and then do the id generation
if needed.
This patch also adds a WARN_ON_ONCE in mark_ptr_or_null_reg()
to catch future breakage.
The _OR_NULL pointer usage in the bpf_iter_reg.ctx_arg_info is
fine because it just happens that the existing id generation after
check_ctx_access() has covered it. It is also using the
reg_type_may_be_null() to decide if id generation is needed or not.
Fixes: af7ec1383361 ("bpf: Add bpf_skc_to_tcp6_sock() helper")
Fixes: eaa6bcb71ef6 ("bpf: Introduce bpf_per_cpu_ptr()")
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201019194212.1050855-1-kafai@fb.com
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A break is not needed if it is preceded by a return.
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20201019173846.1021-1-trix@redhat.com
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Pull arch task_work cleanups from Jens Axboe:
"Two cleanups that don't fit other categories:
- Finally get the task_work_add() cleanup done properly, so we don't
have random 0/1/false/true/TWA_SIGNAL confusing use cases. Updates
all callers, and also fixes up the documentation for
task_work_add().
- While working on some TIF related changes for 5.11, this
TIF_NOTIFY_RESUME cleanup fell out of that. Remove some arch
duplication for how that is handled"
* tag 'arch-cleanup-2020-10-22' of git://git.kernel.dk/linux-block:
task_work: cleanup notification modes
tracehook: clear TIF_NOTIFY_RESUME in tracehook_notify_resume()
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A previous commit changed the notification mode from true/false to an
int, allowing notify-no, notify-yes, or signal-notify. This was
backwards compatible in the sense that any existing true/false user
would translate to either 0 (on notification sent) or 1, the latter
which mapped to TWA_RESUME. TWA_SIGNAL was assigned a value of 2.
Clean this up properly, and define a proper enum for the notification
mode. Now we have:
- TWA_NONE. This is 0, same as before the original change, meaning no
notification requested.
- TWA_RESUME. This is 1, same as before the original change, meaning
that we use TIF_NOTIFY_RESUME.
- TWA_SIGNAL. This uses TIF_SIGPENDING/JOBCTL_TASK_WORK for the
notification.
Clean up all the callers, switching their 0/1/false/true to using the
appropriate TWA_* mode for notifications.
Fixes: e91b48162332 ("task_work: teach task_work_add() to do signal_wake_up()")
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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All the callers currently do this, clean it up and move the clearing
into tracehook_notify_resume() instead.
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
Pull Kbuild updates from Masahiro Yamada:
- Support 'make compile_commands.json' to generate the compilation
database more easily, avoiding stale entries
- Support 'make clang-analyzer' and 'make clang-tidy' for static checks
using clang-tidy
- Preprocess scripts/modules.lds.S to allow CONFIG options in the
module linker script
- Drop cc-option tests from compiler flags supported by our minimal
GCC/Clang versions
- Use always 12-digits commit hash for CONFIG_LOCALVERSION_AUTO=y
- Use sha1 build id for both BFD linker and LLD
- Improve deb-pkg for reproducible builds and rootless builds
- Remove stale, useless scripts/namespace.pl
- Turn -Wreturn-type warning into error
- Fix build error of deb-pkg when CONFIG_MODULES=n
- Replace 'hostname' command with more portable 'uname -n'
- Various Makefile cleanups
* tag 'kbuild-v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (34 commits)
kbuild: Use uname for LINUX_COMPILE_HOST detection
kbuild: Only add -fno-var-tracking-assignments for old GCC versions
kbuild: remove leftover comment for filechk utility
treewide: remove DISABLE_LTO
kbuild: deb-pkg: clean up package name variables
kbuild: deb-pkg: do not build linux-headers package if CONFIG_MODULES=n
kbuild: enforce -Werror=return-type
scripts: remove namespace.pl
builddeb: Add support for all required debian/rules targets
builddeb: Enable rootless builds
builddeb: Pass -n to gzip for reproducible packages
kbuild: split the build log of kallsyms
kbuild: explicitly specify the build id style
scripts/setlocalversion: make git describe output more reliable
kbuild: remove cc-option test of -Werror=date-time
kbuild: remove cc-option test of -fno-stack-check
kbuild: remove cc-option test of -fno-strict-overflow
kbuild: move CFLAGS_{KASAN,UBSAN,KCSAN} exports to relevant Makefiles
kbuild: remove redundant CONFIG_KASAN check from scripts/Makefile.kasan
kbuild: do not create built-in objects for external module builds
...
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This change removes all instances of DISABLE_LTO from
Makefiles, as they are currently unused, and the preferred
method of disabling LTO is to filter out the flags instead.
Note added by Masahiro Yamada:
DISABLE_LTO was added as preparation for GCC LTO, but GCC LTO was
not pulled into the mainline. (https://lkml.org/lkml/2014/4/8/272)
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux
Pull modules updates from Jessica Yu:
"Code cleanups: more informative error messages and statically
initialize init_free_wq to avoid a workqueue warning"
* tag 'modules-for-v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux:
module: statically initialize init section freeing data
module: Add more error message for failed kernel module loading
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Corentin hit the following workqueue warning when running with
CRYPTO_MANAGER_EXTRA_TESTS:
WARNING: CPU: 2 PID: 147 at kernel/workqueue.c:1473 __queue_work+0x3b8/0x3d0
Modules linked in: ghash_generic
CPU: 2 PID: 147 Comm: modprobe Not tainted
5.6.0-rc1-next-20200214-00068-g166c9264f0b1-dirty #545
Hardware name: Pine H64 model A (DT)
pc : __queue_work+0x3b8/0x3d0
Call trace:
__queue_work+0x3b8/0x3d0
queue_work_on+0x6c/0x90
do_init_module+0x188/0x1f0
load_module+0x1d00/0x22b0
I wasn't able to reproduce on x86 or rpi 3b+.
This is
WARN_ON(!list_empty(&work->entry))
from __queue_work(), and it happens because the init_free_wq work item
isn't initialized in time for a crypto test that requests the gcm
module. Some crypto tests were recently moved earlier in boot as
explained in commit c4741b230597 ("crypto: run initcalls for generic
implementations earlier"), which went into mainline less than two weeks
before the Fixes commit.
Avoid the warning by statically initializing init_free_wq and the
corresponding llist.
Link: https://lore.kernel.org/lkml/20200217204803.GA13479@Red/
Fixes: 1a7b7d922081 ("modules: Use vmalloc special flag")
Reported-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Tested-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Tested-on: sun50i-h6-pine-h64
Tested-on: imx8mn-ddr4-evk
Tested-on: sun50i-a64-bananapi-m64
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>
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When kernel module loading failed, user space only get one of the
following error messages:
- ENOEXEC
This is the most confusing one. From corrupted ELF header to bad
WRITE|EXEC flags check introduced by in module_enforce_rwx_sections()
all returns this error number.
- EPERM
This is for blacklisted modules. But mod doesn't do extra explain
on this error either.
- ENOMEM
The only error which needs no explain.
This means, if a user got "Exec format error" from modprobe, it provides
no meaningful way for the user to debug, and will take extra time
communicating to get extra info.
So this patch will add extra error messages for -ENOEXEC and -EPERM
errors, allowing user to do better debugging and reporting.
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull initial set_fs() removal from Al Viro:
"Christoph's set_fs base series + fixups"
* 'work.set_fs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
fs: Allow a NULL pos pointer to __kernel_read
fs: Allow a NULL pos pointer to __kernel_write
powerpc: remove address space overrides using set_fs()
powerpc: use non-set_fs based maccess routines
x86: remove address space overrides using set_fs()
x86: make TASK_SIZE_MAX usable from assembly code
x86: move PAGE_OFFSET, TASK_SIZE & friends to page_{32,64}_types.h
lkdtm: remove set_fs-based tests
test_bitmap: remove user bitmap tests
uaccess: add infrastructure for kernel builds with set_fs()
fs: don't allow splice read/write without explicit ops
fs: don't allow kernel reads and writes without iter ops
sysctl: Convert to iter interfaces
proc: add a read_iter method to proc proc_ops
proc: cleanup the compat vs no compat file ops
proc: remove a level of indentation in proc_get_inode
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Using the read_iter/write_iter interfaces allows for in-kernel users
to set sysctls without using set_fs(). Also, the buffer is a string,
so give it the real type of 'char *', not void *.
[AV: Christoph's fixup folded in]
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull RCU changes from Ingo Molnar:
- Debugging for smp_call_function()
- RT raw/non-raw lock ordering fixes
- Strict grace periods for KASAN
- New smp_call_function() torture test
- Torture-test updates
- Documentation updates
- Miscellaneous fixes
[ This doesn't actually pull the tag - I've dropped the last merge from
the RCU branch due to questions about the series. - Linus ]
* tag 'core-rcu-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (77 commits)
smp: Make symbol 'csd_bug_count' static
kernel/smp: Provide CSD lock timeout diagnostics
smp: Add source and destination CPUs to __call_single_data
rcu: Shrink each possible cpu krcp
rcu/segcblist: Prevent useless GP start if no CBs to accelerate
torture: Add gdb support
rcutorture: Allow pointer leaks to test diagnostic code
rcutorture: Hoist OOM registry up one level
refperf: Avoid null pointer dereference when buf fails to allocate
rcutorture: Properly synchronize with OOM notifier
rcutorture: Properly set rcu_fwds for OOM handling
torture: Add kvm.sh --help and update help message
rcutorture: Add CONFIG_PROVE_RCU_LIST to TREE05
torture: Update initrd documentation
rcutorture: Replace HTTP links with HTTPS ones
locktorture: Make function torture_percpu_rwsem_init() static
torture: document --allcpus argument added to the kvm.sh script
rcutorture: Output number of elapsed grace periods
rcutorture: Remove KCSAN stubs
rcu: Remove unused "cpu" parameter from rcu_report_qs_rdp()
...
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git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu
Pull v5.10 RCU changes from Paul E. McKenney:
- Debugging for smp_call_function().
- Strict grace periods for KASAN. The point of this series is to find
RCU-usage bugs, so the corresponding new RCU_STRICT_GRACE_PERIOD
Kconfig option depends on both DEBUG_KERNEL and RCU_EXPERT, and is
further disabled by dfefault. Finally, the help text includes
a goodly list of scary caveats.
- New smp_call_function() torture test.
- Torture-test updates.
- Documentation updates.
- Miscellaneous fixes.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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csd.2020.09.04a: CPU smp_call_function() torture tests.
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The sparse tool complains as follows:
kernel/smp.c:107:10: warning:
symbol 'csd_bug_count' was not declared. Should it be static?
Because variable is not used outside of smp.c, this commit marks it
static.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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This commit causes csd_lock_wait() to emit diagnostics when a CPU
fails to respond quickly enough to one of the smp_call_function()
family of function calls. These diagnostics are enabled by a new
CSD_LOCK_WAIT_DEBUG Kconfig option that depends on DEBUG_KERNEL.
This commit was inspired by an earlier patch by Josef Bacik.
[ paulmck: Fix for syzbot+0f719294463916a3fc0e@syzkaller.appspotmail.com ]
[ paulmck: Fix KASAN use-after-free issue reported by Qian Cai. ]
[ paulmck: Fix botched nr_cpu_ids comparison per Dan Carpenter. ]
[ paulmck: Apply Peter Zijlstra feedback. ]
Link: https://lore.kernel.org/lkml/00000000000042f21905a991ecea@google.com
Link: https://lore.kernel.org/lkml/0000000000002ef21705a9933cf3@google.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit adds a destination CPU to __call_single_data, and is inspired
by an earlier commit by Peter Zijlstra. This version adds #ifdef to
permit use by 32-bit systems and supplying the destination CPU for all
smp_call_function*() requests, not just smp_call_function_single().
If need be, 32-bit systems could be accommodated by shrinking the flags
field to 16 bits (the atomic_t variant is currently unused) and by
providing only eight bits for CPU on such systems.
It is not clear that the addition of the fields to __call_single_node
are really needed.
[ paulmck: Apply Boqun Feng feedback on 32-bit builds. ]
Link: https://lore.kernel.org/lkml/20200615164048.GC2531@hirez.programming.kicks-ass.net/
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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strictgp.2020.08.24a: Strict grace periods for KASAN testing.
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The "cpu" parameter to rcu_report_qs_rdp() is not used, with rdp->cpu
being used instead. Furtheremore, every call to rcu_report_qs_rdp()
invokes it on rdp->cpu. This commit therefore removes this unused "cpu"
parameter and converts a check of rdp->cpu against smp_processor_id()
to a WARN_ON_ONCE().
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The CONFIG_PREEMPT=n instance of rcu_read_unlock is even more
aggressively than that of CONFIG_PREEMPT=y in deferring reporting
quiescent states to the RCU core. This is just what is wanted in normal
use because it reduces overhead, but the resulting delay is not what
is wanted for kernels built with CONFIG_RCU_STRICT_GRACE_PERIOD=y.
This commit therefore adds an rcu_read_unlock_strict() function that
checks for exceptional conditions, and reports the newly started
quiescent state if it is safe to do so, also doing a spin-delay if
requested via rcutree.rcu_unlock_delay. This commit also adds a call
to rcu_read_unlock_strict() from the CONFIG_PREEMPT=n instance of
__rcu_read_unlock().
[ paulmck: Fixed bug located by kernel test robot <lkp@intel.com> ]
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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A kernel built with CONFIG_RCU_STRICT_GRACE_PERIOD=y needs a quiescent
state to appear very shortly after a CPU has noticed a new grace period.
Placing an RCU reader immediately after this point is ineffective because
this normally happens in softirq context, which acts as a big RCU reader.
This commit therefore introduces a new per-CPU work_struct, which is
used at the end of rcu_core() processing to schedule an RCU read-side
critical section from within a clean environment.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The goal of this series is to increase the probability of tools like
KASAN detecting that an RCU-protected pointer was used outside of its
RCU read-side critical section. Thus far, the approach has been to make
grace periods and callback processing happen faster. Another approach
is to delay the pointer leaker. This commit therefore allows a delay
to be applied to exit from RCU read-side critical sections.
This slowdown is specified by a new rcutree.rcu_unlock_delay kernel boot
parameter that specifies this delay in microseconds, defaulting to zero.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Currently, each CPU discovers the end of a given grace period on its
own time, which is again good for efficiency but bad for fast grace
periods, given that it is things like kfree() within the RCU callbacks
that will cause trouble for pointers leaked from RCU read-side critical
sections. This commit therefore uses on_each_cpu() to IPI each CPU
after grace-period cleanup in order to inform each CPU of the end of
the old grace period in a timely manner, but only in kernels build with
CONFIG_RCU_STRICT_GRACE_PERIOD=y.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Currently, each CPU discovers the beginning of a given grace period
on its own time, which is again good for efficiency but bad for fast
grace periods. This commit therefore uses on_each_cpu() to IPI each
CPU after grace-period initialization in order to inform each CPU of
the new grace period in a timely manner, but only in kernels build with
CONFIG_RCU_STRICT_GRACE_PERIOD=y.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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A given CPU normally notes a new grace period during one RCU_SOFTIRQ,
but avoids reporting the corresponding quiescent state until some later
RCU_SOFTIRQ. This leisurly approach improves efficiency by increasing
the number of update requests served by each grace period, but is not
what is needed for kernels built with CONFIG_RCU_STRICT_GRACE_PERIOD=y.
This commit therefore adds a new rcu_strict_gp_check_qs() function
which, in CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, simply enters and
immediately exist an RCU read-side critical section. If the CPU is
in a quiescent state, the rcu_read_unlock() will attempt to report an
immediate quiescent state. This rcu_strict_gp_check_qs() function is
invoked from note_gp_changes(), so that a CPU just noticing a new grace
period might immediately report a quiescent state for that grace period.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The rcu_preempt_deferred_qs_irqrestore() function is invoked at
the end of an RCU read-side critical section (for example, directly
from rcu_read_unlock()) and, if .need_qs is set, invokes rcu_qs() to
report the new quiescent state. This works, except that rcu_qs() only
updates per-CPU state, leaving reporting of the actual quiescent state
to a later call to rcu_report_qs_rdp(), for example from within a later
RCU_SOFTIRQ instance. Although this approach is exactly what you want if
you are more concerned about efficiency than about short grace periods,
in CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, short grace periods are
the name of the game.
This commit therefore makes rcu_preempt_deferred_qs_irqrestore() directly
invoke rcu_report_qs_rdp() in CONFIG_RCU_STRICT_GRACE_PERIOD=y, thus
shortening grace periods.
Historical note: To the best of my knowledge, causing rcu_read_unlock()
to directly report a quiescent state first appeared in Jim Houston's
and Joe Korty's JRCU. This is the second instance of a Linux-kernel RCU
feature being inspired by JRCU, the first being RCU callback offloading
(as in the RCU_NOCB_CPU Kconfig option).
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The ->rcu_read_unlock_special.b.need_qs field in the task_struct
structure indicates that the RCU core needs a quiscent state from the
corresponding task. The __rcu_read_unlock() function checks this (via
an eventual call to rcu_preempt_deferred_qs_irqrestore()), and if set
reports a quiscent state immediately upon exit from the outermost RCU
read-side critical section.
Currently, this flag is only set when the scheduling-clock interrupt
decides that the current RCU grace period is too old, as in about
one full second too old. But if the kernel has been built with
CONFIG_RCU_STRICT_GRACE_PERIOD=y, we clearly do not want to wait that
long. This commit therefore sets the .need_qs field immediately at the
start of the RCU read-side critical section from within __rcu_read_lock()
in order to unconditionally enlist help from __rcu_read_unlock().
But note the additional check for rcu_state.gp_kthread, which prevents
attempts to awaken RCU's grace-period kthread during early boot before
there is a scheduler. Leaving off this check results in early boot hangs.
So early that there is no console output. Thus, this additional check
fails until such time as RCU's grace-period kthread has been created,
avoiding these empty-console hangs.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The value of DEFAULT_RCU_BLIMIT is normally set to 10, the idea being to
avoid needless response-time degradation due to RCU callback invocation.
However, when CONFIG_RCU_STRICT_GRACE_PERIOD=y it is better to avoid
throttling callback execution in order to better detect pointer
leaks from RCU read-side critical sections. This commit therefore
sets the value of DEFAULT_RCU_BLIMIT to 1000 in kernels built with
CONFIG_RCU_STRICT_GRACE_PERIOD=y.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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If there are idle CPUs, RCU's grace-period kthread will wait several
jiffies before even thinking about polling them. This promotes
efficiency, which is normally a good thing, but when the kernel
has been built with CONFIG_RCU_STRICT_GRACE_PERIOD=y, we care more
about short grace periods. This commit therefore restricts the
default jiffies_till_first_fqs value to zero in kernels built with
CONFIG_RCU_STRICT_GRACE_PERIOD=y, which causes RCU's grace-period kthread
to poll for idle CPUs immediately after starting a grace period.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Because strict RCU grace periods will complete more quickly, they will
experience greater lock contention on each leaf rcu_node structure's
->lock. This commit therefore reduces the leaf fanout in order to reduce
this lock contention.
Note that this also has the effect of reducing the number of CPUs
supported to 16 in the case of CONFIG_RCU_FANOUT_LEAF=2 or 81 in the
case of CONFIG_RCU_FANOUT_LEAF=3. However, greater numbers of CPUs are
probably a bad idea when using CONFIG_RCU_STRICT_GRACE_PERIOD=y. Those
wishing to live dangerously are free to edit their kernel/rcu/Kconfig
files accordingly.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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People running automated tests have asked for a way to make RCU minimize
grace-period duration in order to increase the probability of KASAN
detecting a pointer being improperly leaked from an RCU read-side critical
section, for example, like this:
rcu_read_lock();
p = rcu_dereference(gp);
do_something_with(p); // OK
rcu_read_unlock();
do_something_else_with(p); // BUG!!!
The rcupdate.rcu_expedited boot parameter is a start in this direction,
given that it makes calls to synchronize_rcu() instead invoke the faster
(and more wasteful) synchronize_rcu_expedited(). However, this does
nothing to shorten RCU grace periods that are instead initiated by
call_rcu(), and RCU pointer-leak bugs can involve call_rcu() just as
surely as they can synchronize_rcu().
This commit therefore adds a RCU_STRICT_GRACE_PERIOD Kconfig option
that will be used to shorten normal (non-expedited) RCU grace periods.
This commit also dumps out a message when this option is in effect.
Later commits will actually shorten grace periods.
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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scftorture.2020.08.24a: Torture tests for smp_call_function() and friends.
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This commit further avoids conflation of rcuperf with the kernel's perf
feature by renaming kernel/rcu/rcuperf.c to kernel/rcu/rcuscale.c, and
also by similarly renaming the functions and variables inside this file.
This has the side effect of changing the names of the kernel boot
parameters, so kernel-parameters.txt and ver_functions.sh are also
updated. The rcutorture --torture type was also updated from rcuperf
to rcuscale.
[ paulmck: Fix bugs located by Stephen Rothwell. ]
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Although the test loop does randomly delay, which would provide quiescent
states and so forth, it is possible for there to be a series of long
smp_call_function*() handler runtimes with no delays, which results in
softlockup and RCU CPU stall warning messages. This commit therefore
inserts a cond_resched() into the main test loop.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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On uniprocessor systems, smp_call_function() does nothing. This commit
therefore avoids complaining about the lack of handler accesses in the
single-CPU case where there is no handler.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Currently, CPU-hotplug operations might result in all but two
of (say) 100 CPUs being offline, which in turn might result in
false-positive diagnostics due to overload. This commit therefore
causes scftorture_invoker() kthreads for offline CPUs to loop blocking
for 200 milliseconds at a time, thus continuously adjusting the number
of threads to match the number of online CPUs.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit adds a "default" case to the switch statement in
scftorture_invoke_one() which contains a WARN_ON_ONCE() and an assignment
to ->scfc_out to suppress knock-on warnings. These knock-on warnings
could otherwise cause the user to think that there was a memory-ordering
problem in smp_call_function() instead of a bug in scftorture.c itself.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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The sparse tool complains as follows
kernel/scftorture.c:124:1: warning:
symbol '__pcpu_scope_scf_torture_rand' was not declared. Should it be static?
And this per-CPU variable is not used outside of scftorture.c,
so this commit marks it static.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Detecting smp_call_function() memory misordering requires close timing,
so it is necessary to have the checks immediately before and after
the call to the smp_call_function*() function under test. This commit
therefore inserts barrier() calls to prevent the compiler from optimizing
memory-misordering detection down into the zone of extreme improbability.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit prints error counts on the statistics line and also adds a
"!!!" if any of the counters are non-zero. Allocation failures are
(somewhat) forgiven, but all other errors result in a "FAILURE" print
at the end of the test.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit hoists much of the initialization of the scf_check
structure out of the switch statement, thus saving a few lines of code.
The initialization of the ->scfc_in field remains in each leg of the
switch statement in order to more heavily stress memory ordering.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit moves checking of the ->scfc_out field and the freeing of
the scf_check structure down below the end of switch statement, thus
saving a few lines of code.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit adds checks for memory misordering across calls to and
returns from smp_call_function() in the case where the caller waits.
Misordering results in a splat.
Note that in contrast to smp_call_function_single(), this code does not
test memory ordering into the handler in the no-wait case because none
of the handlers would be able to free the scf_check structure without
introducing heavy synchronization to work out which was last.
[ paulmck: s/GFP_KERNEL/GFP_ATOMIC/ per kernel test robot feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit adds checks for memory misordering across calls to and
returns from smp_call_function_many() in the case where the caller waits.
Misordering results in a splat.
Note that in contrast to smp_call_function_single(), this code does not
test memory ordering into the handler in the no-wait case because none
of the handlers would be able to free the scf_check structure without
introducing heavy synchronization to work out which was last.
[ paulmck: s/GFP_KERNEL/GFP_ATOMIC/ per kernel test robot feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit adds checks for memory misordering across calls to
smp_call_function_single() and also across returns in the case where
the caller waits. Misordering results in a splat.
[ paulmck: s/GFP_KERNEL/GFP_ATOMIC/ per kernel test robot feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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This commit summarizes the per-thread statistics, providing counts of
the number of single, many, and all calls, both no-wait and wait, and,
for the single case, the number where the target CPU was offline.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Currently, can_stop_idle_tick() prints "NOHZ: local_softirq_pending HH"
(where "HH" is the hexadecimal softirq vector number) when one or more
non-RCU softirq handlers are still enabled when checking to stop the
scheduler-tick interrupt. This message is not as enlightening as one
might hope, so this commit changes it to "NOHZ tick-stop error: Non-RCU
local softirq work is pending, handler #HH".
Reported-by: Andy Lutomirski <luto@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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