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Mon, 10 Nov 2025 10:09:13 -0500 X-MC-Unique: qUFs8U_0NA-Z5BLaeSXOpA-1 X-Mimecast-MFC-AGG-ID: qUFs8U_0NA-Z5BLaeSXOpA_1762787352 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0959E180067A; Mon, 10 Nov 2025 15:09:10 +0000 (UTC) Received: from fedora (unknown [10.44.33.158]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 96D4E30044E1; Mon, 10 Nov 2025 15:09:07 +0000 (UTC) Received: by fedora (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 10 Nov 2025 16:09:09 +0100 (CET) Date: Mon, 10 Nov 2025 16:09:05 +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 10.30.177.4 X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: B6F9D1C0015 X-Stat-Signature: kz8dgmc33dirf8deynj9awqie1w8p3xm X-Rspam-User: X-HE-Tag: 1762787358-664946 X-HE-Meta: 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 +1yvgtbm Yi7rHTLnr96X7GcAEt20dbA+vqUCIyKrtvAXmLgCbzYdGUAcin/F1dIhsu0vIy2mHuyqwel32LDMaA9g73OkTrdwUi2byS72FpledlHT/rOnUpQW9UJMB1P6MhPPnO8WTxkBLS6MfnKEkXxcm4Ju5ZewtaoCS9IwoLJzk47YtcpJjqyEYgtkpSK24WJPMeUi0xJlhxfdhRV4+du0jnXsmXDDluz0dhe+ohW5kZbh0pYiJG2E1BpFzPX3Zg17IXrYlTjRFGh6YZ5NKqb3S2jFY44C+20MTVk02R9gU+7kgqEeKNZvspovd9wAy30Hzbbz4Sx40w2uJaDM89dRZ3De8X5TGRHDodhfUCfyx5vbOjH+i8MPmRaKSiKaGYameABQgQU5R/StX7hZibclHsnVBBFE9sRJqALiaA6GWUW83EifPKvT6Yw2O5+kq7A== 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: Hi Cyrill, On 11/10, Cyrill Gorcunov wrote: > > On Sun, Nov 09, 2025 at 06:15:33PM +0100, Oleg Nesterov wrote: > .. > > static int kill_sub_threads(struct task_struct *tsk) > > { > > struct signal_struct *sig = tsk->signal; > > int err = -EINTR; > > > > read_lock(&tasklist_lock); > > spin_lock_irq(&tsk->sighand->siglock); > > if (!((sig->flags & SIGNAL_GROUP_EXIT) || sig->group_exec_task)) { > > sig->group_exec_task = tsk; > > sig->notify_count = -zap_other_threads(tsk); > > Hi Oleg! I somehow manage to miss a moment -- why negative result here? You know, initially I wrote sig->notify_count = 0 - zap_other_threads(tsk); to make it clear that this is not a typo ;) This is for exit_notify() which does /* mt-exec, de_thread() -> wait_for_notify_count() */ if (tsk->signal->notify_count < 0 && !++tsk->signal->notify_count) wake_up_process(tsk->signal->group_exec_task); Then setup_new_exec() sets notify_count > 0 for __exit_signal() which does /* mt-exec, setup_new_exec() -> wait_for_notify_count() */ if (sig->notify_count > 0 && !--sig->notify_count) wake_up_process(sig->group_exec_task); Yes this needs more comments and (with or without this patch) cleanups. Note that exit_notify() and __exit_signal() already (before this patch) use ->notify_count almost the same way, just exit_notify() assumes that notify_count < 0 means the !thread_group_leader() case in de_thread(). Oleg.