linux-kernel - Re: [PATCH v2] signal: Skip the altstack update when not needed

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Date:   Mon, 13 Dec 2021 22:25:37 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Chang S. Bae" <chang.seok.bae@...el.com>,
        linux-kernel@...r.kernel.org
Cc:     dave.hansen@...ux.intel.com, ebiederm@...ssion.com,
        oleg@...hat.com, bp@...en8.de, x86@...nel.org,
        chang.seok.bae@...el.com
Subject: Re: [PATCH v2] signal: Skip the altstack update when not needed

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@...el.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@...el.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>