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- Prevent lock contention on the new sigaltstack lock on the common-case

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path, when no changes have been made to the alternative signal stack.
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Merge tag 'core_urgent_for_v5.16_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull signal handlign fix from Borislav Petkov:

 - Prevent lock contention on the new sigaltstack lock on the
   common-case path, when no changes have been made to the alternative
   signal stack.

* tag 'core_urgent_for_v5.16_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  signal: Skip the altstack update when not needed
This commit is contained in:
Linus Torvalds 2021-12-19 11:46:54 -08:00
commit c36d891d78
1 changed files with 9 additions and 0 deletions
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9
kernel/signal.c
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@ -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;