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Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH] mm: memory-failure: use rcu lock instead of tasklist_lock when collect_procs() To: Matthew Wilcox CC: Andrew Morton , Naoya Horiguchi , Miaohe Lin , , , References: <20230821022534.1381092-1-tongtiangen@huawei.com> From: Tong Tiangen In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.179.234] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To kwepemm600017.china.huawei.com (7.193.23.234) X-CFilter-Loop: Reflected X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 065F61C001D X-Stat-Signature: xm1y9udacu9e6c4bqnwzy4mu3wgq69tu X-HE-Tag: 1692599737-725280 X-HE-Meta: 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 MVVyYWw3 MmlIHOqwwhPUw/SzCcxmUZ2QXW5EJ17rZeXTJYq4ahInOHOinWS3g7aovnxbwAV/oT65mi4J6y9f1RnAb+xvgt9yQX/XGBGBJf83olF4Hmcsfd8BIoXLyylLFAMsYobGiymo0l3zbABeo3Roz6Bm2YZwmtJmINWWTJJQ1VYLFiNlvHNi6V4MVyAQ2TQ== 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: 在 2023/8/21 12:34, Matthew Wilcox 写道: > 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? > > . I've checked that all the paths that call find_early_kill_thread() already hold the rcu lock, and there's really no need to hold the rcu lock here. In the next patch version, here only the comments are modified. Thanks, Tong.