From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Chang S. Bae" <chang.seok.bae@intel.com>,
        linux-kernel@vger.kernel.org
Cc:     dave.hansen@linux.intel.com, ebiederm@xmission.com,
        oleg@redhat.com, bp@alien8.de, x86@kernel.org,
        chang.seok.bae@intel.com
Subject: Re: [PATCH v2] signal: Skip the altstack update when not needed
In-Reply-To: <20211210225503.12734-1-chang.seok.bae@intel.com>
Date:   Mon, 13 Dec 2021 22:25:37 +0100
Message-ID: <87pmq0tcxa.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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>