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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qXwcx-0089YH-Ro; Mon, 21 Aug 2023 04:34:55 +0000 Date: Mon, 21 Aug 2023 05:34:55 +0100 From: Matthew Wilcox To: Tong Tiangen Cc: Andrew Morton , Naoya Horiguchi , Miaohe Lin , wangkefeng.wang@huawei.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: memory-failure: use rcu lock instead of tasklist_lock when collect_procs() Message-ID: References: <20230821022534.1381092-1-tongtiangen@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230821022534.1381092-1-tongtiangen@huawei.com> X-Rspam-User: X-Stat-Signature: bx8gujkhjqg773pybfzw6oh18hhfzk6z X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 11BB8180023 X-HE-Tag: 1692592510-88841 X-HE-Meta: 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 Hh3XLrPa KunTuV7Sta+4yVD9m1+/Ch5YIXAlYnRqYu8hD4izBCmdHLwqYny/Re/mZynZ2ksSDp1wwDz+ultL+/yYvLuazeBjVGN3Eb05KpwlDa+xonXjzfiRRBCPKbJzH+lYXvVYXVNDu0u+C/qR2sNsSvikRg+s9VIu6Kl++OmBcFw7xpWghYyzWR34LL2u2et5PSAZ7V76T X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Aug 21, 2023 at 10:25:34AM +0800, Tong Tiangen wrote: > +++ b/mm/memory-failure.c > @@ -546,24 +546,26 @@ static void kill_procs(struct list_head *to_kill, int forcekill, bool fail, > * Find a dedicated thread which is supposed to handle SIGBUS(BUS_MCEERR_AO) > * on behalf of the thread group. Return task_struct of the (first found) > * dedicated thread if found, and return NULL otherwise. > - * > - * We already hold read_lock(&tasklist_lock) in the caller, so we don't > - * have to call rcu_read_lock/unlock() in this function. > */ > static struct task_struct *find_early_kill_thread(struct task_struct *tsk) > { > struct task_struct *t; > > + rcu_read_lock(); > for_each_thread(tsk, t) { > if (t->flags & PF_MCE_PROCESS) { > if (t->flags & PF_MCE_EARLY) > - return t; > + goto found; > } else { > if (sysctl_memory_failure_early_kill) > - return t; > + goto found; > } > } > - return NULL; > + > + t = NULL; > +found: > + rcu_read_unlock(); > + return t; > } I don't understand why you need to modify find_early_kill_thread() at all. It's still true that the caller holds _a_ lock protecting it; the comment needs to be updated to reflect that it might be the RCU lock or the tasklist_lock (or did you change all callers?), but there's no need for this function to take the RCU lock itself, afaics?