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Tue, 11 Nov 2025 09:09:55 -0500 X-MC-Unique: vw-lvJJNOaevRjFJJf1SIA-1 X-Mimecast-MFC-AGG-ID: vw-lvJJNOaevRjFJJf1SIA_1762870193 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8E8DA195607F; Tue, 11 Nov 2025 14:09:53 +0000 (UTC) Received: from fedora (unknown [10.44.33.247]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 19CF31800576; Tue, 11 Nov 2025 14:09:50 +0000 (UTC) Received: by fedora (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 11 Nov 2025 15:09:53 +0100 (CET) Date: Tue, 11 Nov 2025 15:09:49 +0100 From: Oleg Nesterov To: Cyrill Gorcunov Cc: "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-security-module@vger.kernel.org Subject: Re: [RFC PATCH 2/3] exec: don't wait for zombie threads with cred_guard_mutex held Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 X-Rspamd-Queue-Id: 4406140012 X-Stat-Signature: c7s5wmncxt39jf4ffpsj7j8f1gxza1zy X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1762870198-592801 X-HE-Meta: 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 I2FaOr6G dF1M7BUoPCgk137lksXS/MYmq+J3a6ukoIX730fiueH1z/YpTJO/aB7Qu0eN+KQSs/rEnfeJFydZO3cklTM0uIaigVSaG/dyG2jt7eUQhxjMsb7EpXRfOizX4XTfsgMJNMh1bdMQO3uzDqwmTzhIHrFoAeK5hKsJVUCZvZWubo3vczo7JaqlWeDLvztBB/m6X0UrBmTWt2w4kSG4UkzZ3gq7s9/IX7ZfYqccunxEsvJjORxzxDHgF2kS/Ja2aHCiPtrtPffeJJRzT53quRO5kCxsZhWxPWDezr91ITm5v+TgpGM1qlwQ8ktjBaAiTW1TRaj845HGiysRlqc0zRfuCZT08VU0oW7alKQHG3SuanIplIIDzCQXpW1di60G2s9WjjKC90gphmPn24iZRWiXhQ/sSL7Hq1DuntEQ/AAl3wl44sflPCQZwxMEoaQ== 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: List-Subscribe: List-Unsubscribe: On 11/11, Cyrill Gorcunov wrote: > > Anyway while looking into patch I got wonder why > > +static int wait_for_notify_count(struct task_struct *tsk) > +{ > + for (;;) { > + return -EINTR; > + set_current_state(TASK_KILLABLE); > + if (!tsk->signal->notify_count) > + break; > > We have no any barrier here in fetching @notify_count? I mean updating > this value is done under locks (spin or read/write) in turn condition > test is a raw one. Not a big deal since set_current_state() and schedule() Yes, so I think that, correctness-wise, this doesn't need additional barriers. > but I've > been a bit confused that we don't use some read_once here or something. Yes, this needs READ_ONCE() to avoid the warnings from KCSAN. And in fact this code was written with READ_ONCE() but I removed it before sending this RFC. I was going to do this later. I always forget how KCSAN works, IIUC I also need to add WRITE_ONCE() into exit_notify() and __exit_signal() to make KCSAN happy, even if ->notify_count is always updated under the lock. Same for the "if (me->signal->group_exec_task == me)" check in begin_new_exec(). Right now I would like to know if this RFC (approach) makes any sense, especially because 3/3 adds a user-visible change. Oleg.