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authorChang S. Bae <chang.seok.bae@intel.com>2021-12-10 14:55:03 -0800
committerDave Hansen <dave.hansen@linux.intel.com>2021-12-14 13:08:36 -0800
commit6c3118c32129b4197999a8928ba776bcabd0f5c4 (patch)
tree839fa17c2527f3ce0ad401a9bb57ff0022e598af /kernel/signal.c
parentcabdc3a8475b918e55744f43719b26a82dc8fa6b (diff)
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
Diffstat (limited to 'kernel/signal.c')
-rw-r--r--kernel/signal.c9
1 files changed, 9 insertions, 0 deletions
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;