mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-09-28 21:33:52 +00:00
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: 3aac3ebea0
("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
This commit is contained in:
parent
cabdc3a847
commit
6c3118c321
1 changed files with 9 additions and 0 deletions
|
@ -4185,6 +4185,15 @@ do_sigaltstack (const stack_t *ss, stack_t *oss, unsigned long sp,
|
||||||
ss_mode != 0))
|
ss_mode != 0))
|
||||||
return -EINVAL;
|
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();
|
sigaltstack_lock();
|
||||||
if (ss_mode == SS_DISABLE) {
|
if (ss_mode == SS_DISABLE) {
|
||||||
ss_size = 0;
|
ss_size = 0;
|
||||||
|
|
Loading…
Reference in a new issue