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* tty: Fix lock order in tty_do_resize()Peter Hurley2013-07-252-7/+8
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Commits 6a1c0680cf3ba94356ecd58833e1540c93472a57 and 9356b535fcb71db494fc434acceb79f56d15bda2, respectively 'tty: Convert termios_mutex to termios_rwsem' and 'n_tty: Access termios values safely' introduced a circular lock dependency with console_lock and termios_rwsem. The lockdep report [1] shows that n_tty_write() will attempt to claim console_lock while holding the termios_rwsem, whereas tty_do_resize() may already hold the console_lock while claiming the termios_rwsem. Since n_tty_write() and tty_do_resize() do not contend over the same data -- the tty->winsize structure -- correct the lock dependency by introducing a new lock which specifically serializes access to tty->winsize only. [1] Lockdep report ====================================================== [ INFO: possible circular locking dependency detected ] 3.10.0-0+tip-xeon+lockdep #0+tip Not tainted ------------------------------------------------------- modprobe/277 is trying to acquire lock: (&tty->termios_rwsem){++++..}, at: [<ffffffff81452656>] tty_do_resize+0x36/0xe0 but task is already holding lock: ((fb_notifier_list).rwsem){.+.+.+}, at: [<ffffffff8107aac6>] __blocking_notifier_call_chain+0x56/0xc0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 ((fb_notifier_list).rwsem){.+.+.+}: [<ffffffff810b6d62>] lock_acquire+0x92/0x1f0 [<ffffffff8175b797>] down_read+0x47/0x5c [<ffffffff8107aac6>] __blocking_notifier_call_chain+0x56/0xc0 [<ffffffff8107ab46>] blocking_notifier_call_chain+0x16/0x20 [<ffffffff813d7c0b>] fb_notifier_call_chain+0x1b/0x20 [<ffffffff813d95b2>] register_framebuffer+0x1e2/0x320 [<ffffffffa01043e1>] drm_fb_helper_initial_config+0x371/0x540 [drm_kms_helper] [<ffffffffa01bcb05>] nouveau_fbcon_init+0x105/0x140 [nouveau] [<ffffffffa01ad0af>] nouveau_drm_load+0x43f/0x610 [nouveau] [<ffffffffa008a79e>] drm_get_pci_dev+0x17e/0x2a0 [drm] [<ffffffffa01ad4da>] nouveau_drm_probe+0x25a/0x2a0 [nouveau] [<ffffffff813b13db>] local_pci_probe+0x4b/0x80 [<ffffffff813b1701>] pci_device_probe+0x111/0x120 [<ffffffff814977eb>] driver_probe_device+0x8b/0x3a0 [<ffffffff81497bab>] __driver_attach+0xab/0xb0 [<ffffffff814956ad>] bus_for_each_dev+0x5d/0xa0 [<ffffffff814971fe>] driver_attach+0x1e/0x20 [<ffffffff81496cc1>] bus_add_driver+0x111/0x290 [<ffffffff814982b7>] driver_register+0x77/0x170 [<ffffffff813b0454>] __pci_register_driver+0x64/0x70 [<ffffffffa008a9da>] drm_pci_init+0x11a/0x130 [drm] [<ffffffffa022a04d>] nouveau_drm_init+0x4d/0x1000 [nouveau] [<ffffffff810002ea>] do_one_initcall+0xea/0x1a0 [<ffffffff810c54cb>] load_module+0x123b/0x1bf0 [<ffffffff810c5f57>] SyS_init_module+0xd7/0x120 [<ffffffff817677c2>] system_call_fastpath+0x16/0x1b -> #1 (console_lock){+.+.+.}: [<ffffffff810b6d62>] lock_acquire+0x92/0x1f0 [<ffffffff810430a7>] console_lock+0x77/0x80 [<ffffffff8146b2a1>] con_flush_chars+0x31/0x50 [<ffffffff8145780c>] n_tty_write+0x1ec/0x4d0 [<ffffffff814541b9>] tty_write+0x159/0x2e0 [<ffffffff814543f5>] redirected_tty_write+0xb5/0xc0 [<ffffffff811ab9d5>] vfs_write+0xc5/0x1f0 [<ffffffff811abec5>] SyS_write+0x55/0xa0 [<ffffffff817677c2>] system_call_fastpath+0x16/0x1b -> #0 (&tty->termios_rwsem){++++..}: [<ffffffff810b65c3>] __lock_acquire+0x1c43/0x1d30 [<ffffffff810b6d62>] lock_acquire+0x92/0x1f0 [<ffffffff8175b724>] down_write+0x44/0x70 [<ffffffff81452656>] tty_do_resize+0x36/0xe0 [<ffffffff8146c841>] vc_do_resize+0x3e1/0x4c0 [<ffffffff8146c99f>] vc_resize+0x1f/0x30 [<ffffffff813e4535>] fbcon_init+0x385/0x5a0 [<ffffffff8146a4bc>] visual_init+0xbc/0x120 [<ffffffff8146cd13>] do_bind_con_driver+0x163/0x320 [<ffffffff8146cfa1>] do_take_over_console+0x61/0x70 [<ffffffff813e2b93>] do_fbcon_takeover+0x63/0xc0 [<ffffffff813e67a5>] fbcon_event_notify+0x715/0x820 [<ffffffff81762f9d>] notifier_call_chain+0x5d/0x110 [<ffffffff8107aadc>] __blocking_notifier_call_chain+0x6c/0xc0 [<ffffffff8107ab46>] blocking_notifier_call_chain+0x16/0x20 [<ffffffff813d7c0b>] fb_notifier_call_chain+0x1b/0x20 [<ffffffff813d95b2>] register_framebuffer+0x1e2/0x320 [<ffffffffa01043e1>] drm_fb_helper_initial_config+0x371/0x540 [drm_kms_helper] [<ffffffffa01bcb05>] nouveau_fbcon_init+0x105/0x140 [nouveau] [<ffffffffa01ad0af>] nouveau_drm_load+0x43f/0x610 [nouveau] [<ffffffffa008a79e>] drm_get_pci_dev+0x17e/0x2a0 [drm] [<ffffffffa01ad4da>] nouveau_drm_probe+0x25a/0x2a0 [nouveau] [<ffffffff813b13db>] local_pci_probe+0x4b/0x80 [<ffffffff813b1701>] pci_device_probe+0x111/0x120 [<ffffffff814977eb>] driver_probe_device+0x8b/0x3a0 [<ffffffff81497bab>] __driver_attach+0xab/0xb0 [<ffffffff814956ad>] bus_for_each_dev+0x5d/0xa0 [<ffffffff814971fe>] driver_attach+0x1e/0x20 [<ffffffff81496cc1>] bus_add_driver+0x111/0x290 [<ffffffff814982b7>] driver_register+0x77/0x170 [<ffffffff813b0454>] __pci_register_driver+0x64/0x70 [<ffffffffa008a9da>] drm_pci_init+0x11a/0x130 [drm] [<ffffffffa022a04d>] nouveau_drm_init+0x4d/0x1000 [nouveau] [<ffffffff810002ea>] do_one_initcall+0xea/0x1a0 [<ffffffff810c54cb>] load_module+0x123b/0x1bf0 [<ffffffff810c5f57>] SyS_init_module+0xd7/0x120 [<ffffffff817677c2>] system_call_fastpath+0x16/0x1b other info that might help us debug this: Chain exists of: &tty->termios_rwsem --> console_lock --> (fb_notifier_list).rwsem Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock((fb_notifier_list).rwsem); lock(console_lock); lock((fb_notifier_list).rwsem); lock(&tty->termios_rwsem); *** DEADLOCK *** 7 locks held by modprobe/277: #0: (&__lockdep_no_validate__){......}, at: [<ffffffff81497b5b>] __driver_attach+0x5b/0xb0 #1: (&__lockdep_no_validate__){......}, at: [<ffffffff81497b69>] __driver_attach+0x69/0xb0 #2: (drm_global_mutex){+.+.+.}, at: [<ffffffffa008a6dd>] drm_get_pci_dev+0xbd/0x2a0 [drm] #3: (registration_lock){+.+.+.}, at: [<ffffffff813d93f5>] register_framebuffer+0x25/0x320 #4: (&fb_info->lock){+.+.+.}, at: [<ffffffff813d8116>] lock_fb_info+0x26/0x60 #5: (console_lock){+.+.+.}, at: [<ffffffff813d95a4>] register_framebuffer+0x1d4/0x320 #6: ((fb_notifier_list).rwsem){.+.+.+}, at: [<ffffffff8107aac6>] __blocking_notifier_call_chain+0x56/0xc0 stack backtrace: CPU: 0 PID: 277 Comm: modprobe Not tainted 3.10.0-0+tip-xeon+lockdep #0+tip Hardware name: Dell Inc. Precision WorkStation T5400 /0RW203, BIOS A11 04/30/2012 ffffffff8213e5e0 ffff8802aa2fb298 ffffffff81755f19 ffff8802aa2fb2e8 ffffffff8174f506 ffff8802aa2fa000 ffff8802aa2fb378 ffff8802aa2ea8e8 ffff8802aa2ea910 ffff8802aa2ea8e8 0000000000000006 0000000000000007 Call Trace: [<ffffffff81755f19>] dump_stack+0x19/0x1b [<ffffffff8174f506>] print_circular_bug+0x1fb/0x20c [<ffffffff810b65c3>] __lock_acquire+0x1c43/0x1d30 [<ffffffff810b775e>] ? mark_held_locks+0xae/0x120 [<ffffffff810b78d5>] ? trace_hardirqs_on_caller+0x105/0x1d0 [<ffffffff810b6d62>] lock_acquire+0x92/0x1f0 [<ffffffff81452656>] ? tty_do_resize+0x36/0xe0 [<ffffffff8175b724>] down_write+0x44/0x70 [<ffffffff81452656>] ? tty_do_resize+0x36/0xe0 [<ffffffff81452656>] tty_do_resize+0x36/0xe0 [<ffffffff8146c841>] vc_do_resize+0x3e1/0x4c0 [<ffffffff8146c99f>] vc_resize+0x1f/0x30 [<ffffffff813e4535>] fbcon_init+0x385/0x5a0 [<ffffffff8146a4bc>] visual_init+0xbc/0x120 [<ffffffff8146cd13>] do_bind_con_driver+0x163/0x320 [<ffffffff8146cfa1>] do_take_over_console+0x61/0x70 [<ffffffff813e2b93>] do_fbcon_takeover+0x63/0xc0 [<ffffffff813e67a5>] fbcon_event_notify+0x715/0x820 [<ffffffff81762f9d>] notifier_call_chain+0x5d/0x110 [<ffffffff8107aadc>] __blocking_notifier_call_chain+0x6c/0xc0 [<ffffffff8107ab46>] blocking_notifier_call_chain+0x16/0x20 [<ffffffff813d7c0b>] fb_notifier_call_chain+0x1b/0x20 [<ffffffff813d95b2>] register_framebuffer+0x1e2/0x320 [<ffffffffa01043e1>] drm_fb_helper_initial_config+0x371/0x540 [drm_kms_helper] [<ffffffff8173cbcb>] ? kmemleak_alloc+0x5b/0xc0 [<ffffffff81198874>] ? kmem_cache_alloc_trace+0x104/0x290 [<ffffffffa01035e1>] ? drm_fb_helper_single_add_all_connectors+0x81/0xf0 [drm_kms_helper] [<ffffffffa01bcb05>] nouveau_fbcon_init+0x105/0x140 [nouveau] [<ffffffffa01ad0af>] nouveau_drm_load+0x43f/0x610 [nouveau] [<ffffffffa008a79e>] drm_get_pci_dev+0x17e/0x2a0 [drm] [<ffffffffa01ad4da>] nouveau_drm_probe+0x25a/0x2a0 [nouveau] [<ffffffff8175f162>] ? _raw_spin_unlock_irqrestore+0x42/0x80 [<ffffffff813b13db>] local_pci_probe+0x4b/0x80 [<ffffffff813b1701>] pci_device_probe+0x111/0x120 [<ffffffff814977eb>] driver_probe_device+0x8b/0x3a0 [<ffffffff81497bab>] __driver_attach+0xab/0xb0 [<ffffffff81497b00>] ? driver_probe_device+0x3a0/0x3a0 [<ffffffff814956ad>] bus_for_each_dev+0x5d/0xa0 [<ffffffff814971fe>] driver_attach+0x1e/0x20 [<ffffffff81496cc1>] bus_add_driver+0x111/0x290 [<ffffffffa022a000>] ? 0xffffffffa0229fff [<ffffffff814982b7>] driver_register+0x77/0x170 [<ffffffffa022a000>] ? 0xffffffffa0229fff [<ffffffff813b0454>] __pci_register_driver+0x64/0x70 [<ffffffffa008a9da>] drm_pci_init+0x11a/0x130 [drm] [<ffffffffa022a000>] ? 0xffffffffa0229fff [<ffffffffa022a000>] ? 0xffffffffa0229fff [<ffffffffa022a04d>] nouveau_drm_init+0x4d/0x1000 [nouveau] [<ffffffff810002ea>] do_one_initcall+0xea/0x1a0 [<ffffffff810c54cb>] load_module+0x123b/0x1bf0 [<ffffffff81399a50>] ? ddebug_proc_open+0xb0/0xb0 [<ffffffff813855ae>] ? trace_hardirqs_on_thunk+0x3a/0x3f [<ffffffff810c5f57>] SyS_init_module+0xd7/0x120 [<ffffffff817677c2>] system_call_fastpath+0x16/0x1b Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Remove extra wakeup from pty write() pathPeter Hurley2013-07-241-3/+1
| | | | | | | | | | | | | | | | | | | | | | | Acquiring the write_wait queue spin lock now accounts for the largest slice of cpu time on the tty write path. Two factors contribute to this situation; a overly-pessimistic line discipline write loop which _always_ sets up a wait loop even if i/o will immediately succeed, and on ptys, a wakeup storm from reads and writes. Writer wakeup does not need to be performed by the pty driver. Firstly, since the actual i/o is performed within the write, the line discipline write loop will continue while space remains in the flip buffers. Secondly, when space becomes avail in the line discipline receive buffer (and thus also in the flip buffers), the pty unthrottle re-wakes the writer (non-flow-controlled line disciplines unconditionally unthrottle the driver when data is received). Thus, existing in-kernel i/o is guaranteed to advance. Finally, writer wakeup occurs at the conclusion of the line discipline write (in tty_write_unlock()). This guarantees that any user-space write waiters are woken to continue additional i/o. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Factor LNEXT processing from per-char i/o pathPeter Hurley2013-07-241-72/+94
| | | | | | | | | | | | | LNEXT processing accounts for ~15% of total cpu time in end-to-end tty i/o; factor the lnext test/clear from the per-char i/o path. Instead, attempt to immediately handle the literal next char if not at the end of this received buffer; otherwise, handle the first char of the next received buffer as the literal next char, then continue with normal i/o. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Un-inline single-use functionsPeter Hurley2013-07-241-6/+5
| | | | | | | | gcc will likely inline these single-use functions anyway; remove inline modifier. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Remove overflow tests from receive_buf() pathPeter Hurley2013-07-241-48/+37
| | | | | | | | | | | | Always pre-figure the space available in the read_buf and limit the inbound receive request to that amount. For compatibility reasons with the non-flow-controlled interface, n_tty_receive_buf() will continue filling read_buf until all data has been received or receive_room() returns 0. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Factor PARMRK from normal per-char i/oPeter Hurley2013-07-241-2/+43
| | | | | | | Handle PARMRK processing on the slow per-char i/o path. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Factor ISTRIP and IUCLC receive_buf into separate fnPeter Hurley2013-07-241-12/+32
| | | | | | | | | Convert to modal receive_buf processing; factor char receive processing for unusual termios settings out of normal per-char i/o path. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Split n_tty_receive_char()Peter Hurley2013-07-241-47/+56
| | | | | | | | | Factor 'special' per-char processing into standalone fn, n_tty_receive_char_special(), which handles processing for chars marked in the char_map. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Eliminate char tests from IXANY restart testPeter Hurley2013-07-241-7/+12
| | | | | | | | | | | | Relocate the IXANY restart tty test to code paths where the the received char is not START_CHAR, STOP_CHAR, INTR_CHAR, QUIT_CHAR or SUSP_CHAR. Fixes the condition when ISIG if off and one of INTR_CHAR, QUIT_CHAR or SUSP_CHAR does not restart i/o. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Factor standard per-char i/o into separate fnPeter Hurley2013-07-241-10/+17
| | | | | | | | Simplify __receive_buf() into a dispatch function; perform per-char processing for all other modes not already handled. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Fix build breakage on ppc64Peter Hurley2013-07-241-0/+1
| | | | | | | | | | | | Commit 20bafb3d23d108bc0a896eb8b7c1501f4f649b77 'n_tty: Move buffers into n_tty_data' broke the ppc64 build. Include vmalloc.h for the required function declarations. Reported-by: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Factor tty->closing receive_buf() into separate fnPeter Hurley2013-07-241-11/+39
| | | | | | | | | | | Convert to modal receive_buf() processing; factor receive char processing when tty->closing into n_tty_receive_buf_closing(). Note that EXTPROC when ISTRIP or IUCLC is set continues to be handled by n_tty_receive_char(). Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Special case EXTPROC receive_buf() as raw modePeter Hurley2013-07-241-1/+2
| | | | | | | | | When EXTPROC is set without ISTRIP or IUCLC, processing is identical to raw mode; handle this receiving mode as a special-case of raw mode. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Factor raw mode receive_buf() into separate fnPeter Hurley2013-07-241-5/+19
| | | | | | | | Convert to modal receive_buf() processing; factor raw mode per-char i/o into n_tty_receive_buf_raw(). Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Factor flagged char handling into separate fnPeter Hurley2013-07-241-21/+29
| | | | | | | | | Prepare for modal receive_buf() handling; factor handling for TTY_BREAK, TTY_PARITY, TTY_FRAME and TTY_OVERRUN into n_tty_receive_char_flagged(). Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Factor signal char handling into separate fnPeter Hurley2013-07-241-24/+28
| | | | | | | | | Reduce the monolithic n_tty_receive_char() complexity; factor the handling of INTR_CHAR, QUIT_CHAR and SUSP_CHAR into n_tty_receive_signal_char(). Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Factor 'real raw' receive_buf into standalone fnPeter Hurley2013-07-241-21/+30
| | | | | | | | Convert to modal receive_buf() processing; factor real_raw receive_buf() into n_tty_receive_buf_real_raw(). Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Simplify __receive_buf loop countPeter Hurley2013-07-241-5/+3
| | | | | Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Rename process_char_map to char_mapPeter Hurley2013-07-241-23/+20
| | | | | Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Move buffers into n_tty_dataPeter Hurley2013-07-241-16/+9
| | | | | | | | Reduce pointer reloading and improve locality-of-reference; allocate read_buf and echo_buf within struct n_tty_data. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Remove alias ptrs in __receive_buf()Peter Hurley2013-07-241-7/+6
| | | | | | | | The char and flag buffer local alias pointers, p and f, are unnecessary; remove them. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Fix EOF push handlingPeter Hurley2013-07-242-18/+17
| | | | | | | | | | | | | | | | | | | | In canonical mode, an EOF which is not the first character of the line causes read() to complete and return the number of characters read so far (commonly referred to as EOF push). However, if the previous read() returned because the user buffer was full _and_ the next character is an EOF not at the beginning of the line, read() must not return 0, thus mistakenly indicating the end-of-file condition. The TTY_PUSH flag is used to indicate an EOF was received which is not at the beginning of the line. Because the EOF push condition is evaluated by a thread other than the read(), multiple EOF pushes can cause a premature end-of-file to be indicated. Instead, discover the 'EOF push as first read character' condition from the read() thread itself, and restart the i/o loop if detected. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Avoid false-sharing echo buffer indicesPeter Hurley2013-07-241-5/+4
| | | | | | | | | Separate the head & commit indices from the tail index to avoid cache-line contention (so called 'false-sharing') between concurrent threads. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Eliminate counter in __process_echoesPeter Hurley2013-07-241-8/+1
| | | | | | | | | Since neither echo_commit nor echo_tail can change for the duration of __process_echoes loop, substitute index comparison for the snapshot counter. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Only flush echo output if actually outputPeter Hurley2013-07-241-8/+10
| | | | | | | | Don't have the driver flush received echoes if no echoes were actually output. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Process echoes in blocksPeter Hurley2013-07-241-23/+47
| | | | | | | | | | | | | | | Byte-by-byte echo output is painfully slow, requiring a lock/unlock cycle for every input byte. Instead, perform the echo output in blocks of 256 characters, and at least once per flip buffer receive. Enough space is reserved in the echo buffer to guarantee a full block can be saved without overrunning the echo output. Overrun is prevented by discarding the oldest echoes until enough space exists in the echo buffer to receive at least a full block of new echoes. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Eliminate echo_commit memory barrierPeter Hurley2013-07-241-11/+20
| | | | | | | Use output_lock mutex as a memory barrier when storing echo_commit. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Remove echo_lockPeter Hurley2013-07-241-47/+28
| | | | | | | | | | | | | | | | | Adding data to echo_buf (via add_echo_byte()) is guaranteed to be single-threaded, since all callers are from the n_tty_receive_buf() path. Processing the echo_buf can be called from either the n_tty_receive_buf() path or the n_tty_write() path; however, these callers are already serialized by output_lock. Publish cumulative echo_head changes to echo_commit; process echo_buf from echo_tail to echo_commit; remove echo_lock. On echo_buf overrun, claim output_lock to serialize changes to echo_tail. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Replace echo_cnt with computed valuePeter Hurley2013-07-241-13/+7
| | | | | | | | Prepare for lockless echo_buf handling; compute current byte count of echo_buf from head and tail indices. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Use separate head and tail indices for echo_bufPeter Hurley2013-07-241-53/+35
| | | | | | | | | | | Instead of using a single index to track the current echo_buf position, use a head index when adding to the buffer and a tail index when consuming from the buffer. Allow these head and tail indices to wrap at max representable value; perform modulo reduction via helper functions when accessing the buffer. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Remove unused echo_overrun fieldPeter Hurley2013-07-241-7/+1
| | | | | | | The echo_overrun field is only assigned and never tested; remove it. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Remove private constant from global namespacePeter Hurley2013-07-241-0/+10
| | | | | | | | TTY_BUFFER_PAGE is only used within drivers/tty/tty_buffer.c; relocate to that file scope. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Fix unsafe vt paste_selection()Peter Hurley2013-07-242-14/+51
| | | | | | | | | | Convert the tty_buffer_flush() exclusion mechanism to a public interface - tty_buffer_lock/unlock_exclusive() - and use the interface to safely write the paste selection to the line discipline. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Merge __tty_flush_buffer() into lone call sitePeter Hurley2013-07-241-23/+6
| | | | | | | | __tty_flush_buffer() is now only called by tty_flush_buffer(); merge functions. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Use non-atomic state to signal flip buffer flush pendingPeter Hurley2013-07-241-3/+4
| | | | | | | | | | | Atomic bit ops are no longer required to indicate a flip buffer flush is pending, as the flush_mutex is sufficient barrier. Remove the unnecessary port .iflags field and localize flip buffer state to struct tty_bufhead. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Only perform flip buffer flush from tty_buffer_flush()Peter Hurley2013-07-241-42/+21
| | | | | | | | | | | | Now that dropping the buffer lock is not necessary (as result of converting the spin lock to a mutex), the flip buffer flush no longer needs to be handled by the buffer work. Simply signal a flush is required; the buffer work will exit the i/o loop, which allows tty_buffer_flush() to proceed. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Ensure single-threaded flip buffer consumer with mutexPeter Hurley2013-07-242-21/+21
| | | | | | | | | | | The buffer work may race with parallel tty_buffer_flush. Use a mutex to guarantee exclusive modify access to the head flip buffer. Remove the unneeded spin lock. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Make driver-side flip buffers locklessPeter Hurley2013-07-241-27/+4
| | | | | | | | | | | Driver-side flip buffer input is already single-threaded; 'publish' the .next link as the last operation on the tail buffer so the 'consumer' sees the already-completed flip buffer. The commit buffer index is already 'published' by driver-side functions. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Track flip buffer memory limit atomicallyPeter Hurley2013-07-242-13/+34
| | | | | | | | | | | | Lockless flip buffers require atomically updating the bytes-in-use watermark. The pty driver also peeks at the watermark value to limit memory consumption to a much lower value than the default; query the watermark with new fn, tty_buffer_space_avail(). Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Simplify flip buffer list with 0-sized sentinelPeter Hurley2013-07-241-31/+18
| | | | | | | | | | | | | | | Use a 0-sized sentinel to avoid assigning the head ptr from the driver side thread. This also eliminates testing head/tail for NULL. When the sentinel is first 'consumed' by the buffer work (or by tty_buffer_flush()), it is detached from the list but not freed nor added to the free list. Both buffer work and tty_buffer_flush() continue to preserve at least 1 flip buffer to which head & tail is pointed. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Use lockless flip buffer free listPeter Hurley2013-07-241-17/+12
| | | | | | | | | | | | In preparation for lockless flip buffers, make the flip buffer free list lockless. NB: using llist is not the optimal solution, as the driver and buffer work may contend over the llist head unnecessarily. However, test measurements indicate this contention is low. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Use generic names for flip buffer list cursorsPeter Hurley2013-07-241-10/+10
| | | | | Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Merge tty_buffer_find() into tty_buffer_alloc()Peter Hurley2013-07-241-32/+18
| | | | | | | | | tty_buffer_find() implements a simple free list lookaside cache. Merge this functionality into tty_buffer_alloc() to reflect the more traditional alloc/free symmetry. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Factor flip buffer initialization into helper functionPeter Hurley2013-07-241-9/+12
| | | | | | | Factor shared code; prepare for adding 0-sized sentinel flip buffer. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Fix flip buffer free listPeter Hurley2013-07-241-6/+10
| | | | | | | | | | | Since flip buffers are size-aligned to 256 bytes and all flip buffers 512-bytes or larger are not added to the free list, the free list only contains 256-byte flip buffers. Remove the list search when allocating a new flip buffer. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Compute flip buffer ptrsPeter Hurley2013-07-241-12/+10
| | | | | | | | | | The char_buf_ptr and flag_buf_ptr values are trivially derived from the .data field offset; compute values as needed. Fixes a long-standing type-mismatch with the char and flag ptrs. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Queue buffer work on any available cpuPeter Hurley2013-07-241-1/+1
| | | | | | | | | Scheduling buffer work on the same cpu as the read() thread limits the parallelism now possible between the receive_buf path and the n_tty_read() path. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Special case pty flow controlPeter Hurley2013-07-241-0/+14
| | | | | | | | | | | | | | | The pty driver forces ldisc flow control on, regardless of available receive buffer space, so the writer can be woken whenever unthrottle is called. However, this 'forced throttle' has performance consequences, as multiple atomic operations are necessary to unthrottle and perform the write wakeup for every input line (in canonical mode). Instead, short-circuit the unthrottle if the tty is a pty and perform the write wakeup directly. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Move n_tty_write_wakeup() to avoid forward declarationPeter Hurley2013-07-241-16/+15
| | | | | | | Prepare to special case pty flow control; avoid forward declaration. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* n_tty: Factor throttle/unthrottle into helper functionsPeter Hurley2013-07-241-35/+46
| | | | | | | | Prepare for special handling of pty throttle/unthrottle; factor flow control into helper functions. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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