path: root/kernel/signal.c
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authorLinus Torvalds <torvalds@linux-foundation.org>2020-12-16 12:33:35 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2020-12-16 12:33:35 -0800
commit005b2a9dc819a1265a8c765595f8f6d88d6173d9 (patch)
tree688107572f6b3e017fc7ccf54f552c6a30441a79 /kernel/signal.c
parent5ee863bec794f30bdf7fdf57ce0d9f579b0d1aa3 (diff)
parent355fb9e2b78e78b38ec00f5cd9b05c6aceb98335 (diff)
Merge tag 'tif-task_work.arch-2020-12-14' of git://git.kernel.dk/linux-block
Pull TIF_NOTIFY_SIGNAL updates from Jens Axboe: "This sits on top of of the core entry/exit and x86 entry branch from the tip tree, which contains the generic and x86 parts of this work. Here we convert the rest of the archs to support TIF_NOTIFY_SIGNAL. With that done, we can get rid of JOBCTL_TASK_WORK from task_work and signal.c, and also remove a deadlock work-around in io_uring around knowing that signal based task_work waking is invoked with the sighand wait queue head lock. The motivation for this work is to decouple signal notify based task_work, of which io_uring is a heavy user of, from sighand. The sighand lock becomes a huge contention point, particularly for threaded workloads where it's shared between threads. Even outside of threaded applications it's slower than it needs to be. Roman Gershman <romger@amazon.com> reported that his networked workload dropped from 1.6M QPS at 80% CPU to 1.0M QPS at 100% CPU after io_uring was changed to use TIF_NOTIFY_SIGNAL. The time was all spent hammering on the sighand lock, showing 57% of the CPU time there [1]. There are further cleanups possible on top of this. One example is TIF_PATCH_PENDING, where a patch already exists to use TIF_NOTIFY_SIGNAL instead. Hopefully this will also lead to more consolidation, but the work stands on its own as well" [1] https://github.com/axboe/liburing/issues/215 * tag 'tif-task_work.arch-2020-12-14' of git://git.kernel.dk/linux-block: (28 commits) io_uring: remove 'twa_signal_ok' deadlock work-around kernel: remove checking for TIF_NOTIFY_SIGNAL signal: kill JOBCTL_TASK_WORK io_uring: JOBCTL_TASK_WORK is no longer used by task_work task_work: remove legacy TWA_SIGNAL path sparc: add support for TIF_NOTIFY_SIGNAL riscv: add support for TIF_NOTIFY_SIGNAL nds32: add support for TIF_NOTIFY_SIGNAL ia64: add support for TIF_NOTIFY_SIGNAL h8300: add support for TIF_NOTIFY_SIGNAL c6x: add support for TIF_NOTIFY_SIGNAL alpha: add support for TIF_NOTIFY_SIGNAL xtensa: add support for TIF_NOTIFY_SIGNAL arm: add support for TIF_NOTIFY_SIGNAL microblaze: add support for TIF_NOTIFY_SIGNAL hexagon: add support for TIF_NOTIFY_SIGNAL csky: add support for TIF_NOTIFY_SIGNAL openrisc: add support for TIF_NOTIFY_SIGNAL sh: add support for TIF_NOTIFY_SIGNAL um: add support for TIF_NOTIFY_SIGNAL ...
Diffstat (limited to 'kernel/signal.c')
1 files changed, 0 insertions, 22 deletions
diff --git a/kernel/signal.c b/kernel/signal.c
index c37170655171..5736c55aaa1a 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2555,14 +2555,12 @@ bool get_signal(struct ksignal *ksig)
* that the arch handlers don't all have to do it. If we get here
* without TIF_SIGPENDING, just exit after running signal work.
if (test_thread_flag(TIF_NOTIFY_SIGNAL))
if (!task_sigpending(current))
return false;
if (unlikely(uprobe_deny_signal()))
return false;
@@ -2576,26 +2574,6 @@ bool get_signal(struct ksignal *ksig)
- /*
- * Make sure we can safely read ->jobctl() in task_work add. As Oleg
- * states:
- *
- * It pairs with mb (implied by cmpxchg) before READ_ONCE. So we
- * roughly have
- *
- * task_work_add: get_signal:
- * STORE(task->task_works, new_work); STORE(task->jobctl);
- * mb(); mb();
- * LOAD(task->jobctl); LOAD(task->task_works);
- *
- * and we can rely on STORE-MB-LOAD [ in task_work_add].
- */
- smp_store_mb(current->jobctl, current->jobctl & ~JOBCTL_TASK_WORK);
- if (unlikely(current->task_works)) {
- spin_unlock_irq(&sighand->siglock);
- task_work_run();
- goto relock;
- }
* Every stopped thread goes here after wakeup. Check to see if

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