From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793214217; b=CVHjXsCLKr+DMleQVoLg9ffw3AIe4+jG7b0EzfiA28OA5veBsInLAQg7cy6RY85Jib7/ eiLEcfsRO1OjlbsPlTPBeNI+mQCdlgBWrBj06W8vZyZl6FWUIuHYUe5O7CwZ8Ao4JU02A nPdskcgQPZqu66PUztYy3KEetDCdbBBpIYpcG9l9S2ToYGTW8CSdDOUStCcytNNB9ibbu Ud77cWsnEVeStPGsGMvD8sglqlx5ChIXrMVQOI3CncYQEb4xkqKkjw9QX6q329Tng0LcA 0QAfCog1pfduYlpxy4FwXVek5bSWMY7Mz71a/+DYEH1vk4nvFwmbBwl/Bb361w8nZyA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793214217; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=C4ny3E/DJgx+poTEqKzRisjOUtArQtOkrV3V2Ih9C3w=; b=M1K6FqwLvkLW2loNo3DMvNgNPWDpmZAtjLXU3BAaTcDTMkn8W/Yf2v6M4QhDQ2oqt+mt KvOYjBho7lYgw6IEei6hftGEIG4P5O0nkismhhSYbnpCONu6pvXAhjM0+vSmkluWOSiNy QzynsSO2fkB2bXik0ujP7NmvYNKEJ3/+19EJf+ZU4lRILcJroy6voyC92mcVNNo+OB7KL FqysjRC00E5SOkcr6GLU2QxvYzIGoTNruuGjICJzMJ7X6SsBS9w7HebTRjmqeUFX6TVNs VTYDUc3FWVRl7soAUKuN715FLrR8azuP5oHG4GJYUYsNYCytVCGOnMkROYUq5K+KQmQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=aGRJMFpG; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2C0F560A2620 for ; Wed, 28 Oct 2026 19:03:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=aGRJMFpG Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7AA041F013CA; Wed, 28 Oct 2026 19:03:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793214217; bh=C4ny3E/DJgx+poTEqKzRisjOUtArQtOkrV3V2Ih9C3w=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=aGRJMFpGxfHYxLDfD7frrEvOGd8RxOJuxylXC9yA17+cfxdJPUJIeMd+pA1VlIJ79 EguWhhR5KFIWzixvcW/K4yGVV1NWo9URYQ0VMb6m9Vui8VYnA9ikqIyz3IpHlsSlVV iCGfURVSWNQU1dgxw6Bj30bZ/RhUxxmFj25fglhoHvIWnr8t1doe5ZJwl9fkWG3InJ EgLCbEW3jSeTiMY5lH1zMZIUPGyDZ6I+q6S3PnAF37gEip7CHYxcgTMWyCObKQEjUO gQXUUvB3pctZm8Rf9UVBItUyUCqfASkg0LEeWWnMwk8egprLEAA494p45D1ka19OMC Yrp4wZIEmJKcA== From: Sasha Levin To: stable@vger.kernel.org Cc: Christian Brauner , Oleg Nesterov , Sasha Levin Subject: [PATCH 6.12.y 2/2] fork: don't create io threads once PF_POSTCOREDUMP is set Date: Wed, 28 Oct 2026 15:03:34 -0400 Message-ID: <20261028190310.2073874-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261028190310.2073874-1-sashal@kernel.org> References: <2026102850-unleveled-version-e04b@gregkh> <20261028190310.2073874-1-sashal@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Christian Brauner [ Upstream commit 1f978881ce6c9ac4f4d4a7b6a6e52339eadcd350 ] zap_process() skips every thread that already has PF_POSTCOREDUMP set. Such a thread is past synchronize_group_exit(), so a coredump can't catch it anymore. It isn't counted in core_state->threads_remaining and it isn't sent SIGKILL. do_exit() sets PF_POSTCOREDUMP in synchronize_group_exit() and calls io_uring_files_cancel() right after that. The cancellation runs task work and a create_worker_cb() that io-wq queued before the exit creates a new io-wq worker from there. If another thread started a coredump in the meantime that worker joins a thread-group which is already being dumped. zap_process() never saw it so it was never counted. But when it exits it sees signal->core_state in synchronize_group_exit() and decrements threads_remaining like any other thread. So the count reaches zero one thread early and the dumper leaves coredump_wait_inactive() while a thread it counted is still running. The task has no fatal signal pending because zap_process() deliberately didn't send it one, and it never went through get_signal() so it doesn't have PF_SIGNALED either. Refuse to create an io thread when the creator has PF_POSTCOREDUMP. That costs nothing. io_uring_files_cancel() raises IO_WQ_BIT_EXIT before it runs any task work, so a worker created from there only ever gets to exit again, and io_should_retry_thread() doesn't retry -EINTR. Clearing PF_POSTCOREDUMP for the new thread in copy_process() was the other option. It makes the worker a thread like any other, but it only helps while the dump hasn't started. A worker born after zap_process() has run is invisible to it whatever its flags say and still decrements threads_remaining on the way out. Refusing to create it covers both, and then no task is ever born with the flag, so there is nothing to clear. Moving io_uring_files_cancel() ahead of synchronize_group_exit() closes the same window. It runs the cancellation, and whatever that can block on, before the thread announces itself to the dumper. A thread that blocks there never reaches coredump_task_exit() at all, so the dumper ends up waiting for a thread that never parks. Refusing the creation leaves the cancellation where it is. But it's very ugly to run io_uring work even before we did all the generic exit work. Fixes: 92307383082d ("coredump: Don't perform any cleanups before dumping core") Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260921-work-coredump-fixes-v3-14-8e4adb1619e6@kernel.org Acked-by: Oleg Nesterov Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Sasha Levin --- kernel/fork.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index c82956f8fc9d5..140a615daf42e 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2774,8 +2774,8 @@ struct task_struct *create_io_thread(int (*fn)(void *), void *arg, int node) .user_worker = 1, }; - /* A creator past its fatal signal gets no thread. */ - if (current->flags & PF_SIGNALED) + /* A creator past its fatal signal or its coredump point gets no thread. */ + if (current->flags & (PF_SIGNALED | PF_POSTCOREDUMP)) return ERR_PTR(-EINTR); return copy_process(NULL, 0, node, &args); -- 2.53.0