* [PATCH v2] signal: Skip the altstack update when not needed
@ 2021-12-10 22:55 Chang S. Bae
2021-12-13 21:25 ` Thomas Gleixner
2021-12-14 21:12 ` [tip: sched/urgent] " tip-bot2 for Chang S. Bae
0 siblings, 2 replies; 4+ messages in thread
From: Chang S. Bae @ 2021-12-10 22:55 UTC (permalink / raw)
To: linux-kernel; +Cc: tglx, dave.hansen, ebiederm, oleg, bp, x86, chang.seok.bae
== Background ==
Support for large, "dynamic" fpstates was recently merged. This
included code to ensure that sigaltstacks are sufficiently sized for
these large states. A new lock was added to remove races between
enabling large features and setting up sigaltstacks.
== Problem ==
The new lock (sigaltstack_lock()) is acquired in the sigreturn path
before restoring the old sigaltstack. Unfortunately, contention on the
new lock causes a measurable signal handling performance regression [1].
However, the common case is that no *changes* are made to the
sigaltstack state at sigreturn.
== Solution ==
do_sigaltstack() acquires sigaltstack_lock() and is used for both
sys_sigaltstack() and restoring the sigaltstack in sys_sigreturn().
Check for changes to the sigaltstack before taking the lock. If no
changes were made, return before acquiring the lock.
This removes lock contention from the common-case sigreturn path.
Reported-by: kernel test robot <oliver.sang@intel.com>
[1] https://lore.kernel.org/lkml/20211207012128.GA16074@xsang-OptiPlex-9020/
Fixes: 3aac3ebea08f ("x86/signal: Implement sigaltstack size validation")
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
---
Changes from v1:
* Rewrite the changelog. (Dave Hansen)
* Add the code comment. (Dave Hansen)
---
kernel/signal.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/kernel/signal.c b/kernel/signal.c
index a629b11bf3e0..dfcee3888b00 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -4185,6 +4185,15 @@ do_sigaltstack (const stack_t *ss, stack_t *oss, unsigned long sp,
ss_mode != 0))
return -EINVAL;
+ /*
+ * Return before taking any locks if no actual
+ * sigaltstack changes were requested.
+ */
+ if (t->sas_ss_sp == (unsigned long)ss_sp &&
+ t->sas_ss_size == ss_size &&
+ t->sas_ss_flags == ss_flags)
+ return 0;
+
sigaltstack_lock();
if (ss_mode == SS_DISABLE) {
ss_size = 0;
--
2.17.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2] signal: Skip the altstack update when not needed
2021-12-10 22:55 [PATCH v2] signal: Skip the altstack update when not needed Chang S. Bae
@ 2021-12-13 21:25 ` Thomas Gleixner
2021-12-14 1:01 ` Bae, Chang Seok
2021-12-14 21:12 ` [tip: sched/urgent] " tip-bot2 for Chang S. Bae
1 sibling, 1 reply; 4+ messages in thread
From: Thomas Gleixner @ 2021-12-13 21:25 UTC (permalink / raw)
To: Chang S. Bae, linux-kernel
Cc: dave.hansen, ebiederm, oleg, bp, x86, chang.seok.bae
On Fri, Dec 10 2021 at 14:55, Chang S. Bae wrote:
> do_sigaltstack() acquires sigaltstack_lock() and is used for both
> sys_sigaltstack() and restoring the sigaltstack in sys_sigreturn().
> Check for changes to the sigaltstack before taking the lock. If no
> changes were made, return before acquiring the lock.
>
> This removes lock contention from the common-case sigreturn path.
>
> Reported-by: kernel test robot <oliver.sang@intel.com>
> [1] https://lore.kernel.org/lkml/20211207012128.GA16074@xsang-OptiPlex-9020/
> Fixes: 3aac3ebea08f ("x86/signal: Implement sigaltstack size validation")
> Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] signal: Skip the altstack update when not needed
2021-12-13 21:25 ` Thomas Gleixner
@ 2021-12-14 1:01 ` Bae, Chang Seok
0 siblings, 0 replies; 4+ messages in thread
From: Bae, Chang Seok @ 2021-12-14 1:01 UTC (permalink / raw)
To: Thomas Gleixner; +Cc: LKML, dave.hansen, ebiederm, oleg, bp, x86
On Dec 13, 2021, at 13:25, Thomas Gleixner <tglx@linutronix.de> wrote:
>
> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Thanks!
Chang
^ permalink raw reply [flat|nested] 4+ messages in thread
* [tip: sched/urgent] signal: Skip the altstack update when not needed
2021-12-10 22:55 [PATCH v2] signal: Skip the altstack update when not needed Chang S. Bae
2021-12-13 21:25 ` Thomas Gleixner
@ 2021-12-14 21:12 ` tip-bot2 for Chang S. Bae
1 sibling, 0 replies; 4+ messages in thread
From: tip-bot2 for Chang S. Bae @ 2021-12-14 21:12 UTC (permalink / raw)
To: linux-tip-commits
Cc: kernel test robot, Chang S. Bae, Dave Hansen, Thomas Gleixner,
x86, linux-kernel
The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: 6c3118c32129b4197999a8928ba776bcabd0f5c4
Gitweb: https://git.kernel.org/tip/6c3118c32129b4197999a8928ba776bcabd0f5c4
Author: Chang S. Bae <chang.seok.bae@intel.com>
AuthorDate: Fri, 10 Dec 2021 14:55:03 -08:00
Committer: Dave Hansen <dave.hansen@linux.intel.com>
CommitterDate: Tue, 14 Dec 2021 13:08:36 -08:00
signal: Skip the altstack update when not needed
== Background ==
Support for large, "dynamic" fpstates was recently merged. This
included code to ensure that sigaltstacks are sufficiently sized for
these large states. A new lock was added to remove races between
enabling large features and setting up sigaltstacks.
== Problem ==
The new lock (sigaltstack_lock()) is acquired in the sigreturn path
before restoring the old sigaltstack. Unfortunately, contention on the
new lock causes a measurable signal handling performance regression [1].
However, the common case is that no *changes* are made to the
sigaltstack state at sigreturn.
== Solution ==
do_sigaltstack() acquires sigaltstack_lock() and is used for both
sys_sigaltstack() and restoring the sigaltstack in sys_sigreturn().
Check for changes to the sigaltstack before taking the lock. If no
changes were made, return before acquiring the lock.
This removes lock contention from the common-case sigreturn path.
[1] https://lore.kernel.org/lkml/20211207012128.GA16074@xsang-OptiPlex-9020/
Fixes: 3aac3ebea08f ("x86/signal: Implement sigaltstack size validation")
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20211210225503.12734-1-chang.seok.bae@intel.com
---
kernel/signal.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/kernel/signal.c b/kernel/signal.c
index a629b11..dfcee38 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -4185,6 +4185,15 @@ do_sigaltstack (const stack_t *ss, stack_t *oss, unsigned long sp,
ss_mode != 0))
return -EINVAL;
+ /*
+ * Return before taking any locks if no actual
+ * sigaltstack changes were requested.
+ */
+ if (t->sas_ss_sp == (unsigned long)ss_sp &&
+ t->sas_ss_size == ss_size &&
+ t->sas_ss_flags == ss_flags)
+ return 0;
+
sigaltstack_lock();
if (ss_mode == SS_DISABLE) {
ss_size = 0;
^ permalink raw reply related [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-12-14 21:12 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2021-12-10 22:55 [PATCH v2] signal: Skip the altstack update when not needed Chang S. Bae
2021-12-13 21:25 ` Thomas Gleixner
2021-12-14 1:01 ` Bae, Chang Seok
2021-12-14 21:12 ` [tip: sched/urgent] " tip-bot2 for Chang S. Bae
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