Commit 005b2a9d authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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
  ...
parents 5ee863be 355fb9e2

arch/alpha/include/asm/thread_info.h

+2 −0
Original line number Diff line number Diff line
@@ -62,6 +62,7 @@ register struct thread_info *__current_thread_info __asm__("$8"); 
#define TIF_SIGPENDING		2	/* signal pending */

#define TIF_NEED_RESCHED	3	/* rescheduling necessary */

#define TIF_SYSCALL_AUDIT	4	/* syscall audit active */

#define TIF_NOTIFY_SIGNAL	5	/* signal notifications exist */

#define TIF_DIE_IF_KERNEL	9	/* dik recursion lock */

#define TIF_MEMDIE		13	/* is terminating due to OOM killer */

#define TIF_POLLING_NRFLAG	14	/* idle is polling for TIF_NEED_RESCHED */
@@ -71,6 +72,7 @@ register struct thread_info *__current_thread_info __asm__("$8"); 
#define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)

#define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)

#define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)

#define _TIF_NOTIFY_SIGNAL	(1<<TIF_NOTIFY_SIGNAL)

#define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)



/* Work to do on interrupt/exception return.  */

arch/alpha/kernel/entry.S

+1 −1
Original line number Diff line number Diff line
@@ -544,7 +544,7 @@ $ret_success: 
	.align	4

	.type	work_pending, @function

work_pending:

	and	$17, _TIF_NOTIFY_RESUME | _TIF_SIGPENDING, $2

	and	$17, _TIF_NOTIFY_RESUME | _TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL, $2

	bne	$2, $work_notifysig



$work_resched:

arch/alpha/kernel/signal.c

+1 −1
Original line number Diff line number Diff line
@@ -527,7 +527,7 @@ do_work_pending(struct pt_regs *regs, unsigned long thread_flags, 
			schedule();

		} else {

			local_irq_enable();

			if (thread_flags & _TIF_SIGPENDING) {

			if (thread_flags & (_TIF_SIGPENDING|_TIF_NOTIFY_SIGNAL)) {

				do_signal(regs, r0, r19);

				r0 = 0;

			} else {

arch/arc/include/asm/thread_info.h

+3 −1
Original line number Diff line number Diff line
@@ -79,6 +79,7 @@ static inline __attribute_const__ struct thread_info *current_thread_info(void) 
#define TIF_SIGPENDING		2	/* signal pending */

#define TIF_NEED_RESCHED	3	/* rescheduling necessary */

#define TIF_SYSCALL_AUDIT	4	/* syscall auditing active */

#define TIF_NOTIFY_SIGNAL	5	/* signal notifications exist */

#define TIF_SYSCALL_TRACE	15	/* syscall trace active */



/* true if poll_idle() is polling TIF_NEED_RESCHED */
@@ -89,11 +90,12 @@ static inline __attribute_const__ struct thread_info *current_thread_info(void) 
#define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)

#define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)

#define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)

#define _TIF_NOTIFY_SIGNAL	(1<<TIF_NOTIFY_SIGNAL)

#define _TIF_MEMDIE		(1<<TIF_MEMDIE)



/* work to do on interrupt/exception return */

#define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_SIGPENDING | \

				 _TIF_NOTIFY_RESUME)

				 _TIF_NOTIFY_RESUME | _TIF_NOTIFY_SIGNAL)



/*

 * _TIF_ALLWORK_MASK includes SYSCALL_TRACE, but we don't need it.

arch/arc/kernel/entry.S

+2 −1
Original line number Diff line number Diff line
@@ -307,7 +307,8 @@ resume_user_mode_begin: 
	mov r0, sp	; pt_regs for arg to do_signal()/do_notify_resume()



	GET_CURR_THR_INFO_FLAGS   r9

	bbit0  r9, TIF_SIGPENDING, .Lchk_notify_resume

	and.f  0,  r9, TIF_SIGPENDING|TIF_NOTIFY_SIGNAL

	bz .Lchk_notify_resume



	; Normal Trap/IRQ entry only saves Scratch (caller-saved) regs

	; in pt_reg since the "C" ABI (kernel code) will automatically

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