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=1793201636; b=hDJkXgk6nYd7ajgV1WHJ9gcotOjKq4BURXMxR4ynoXaCVu057rpiHacI1hKtS9yxCg3y EgXdHiaUe1dzDAsWmfZLLGroNVIdDQ6GK+8sEdh6wq57hwsPOEz8dhboKaC/MWnPspmjR tDAHUdou4m4JfMAx8BgPYD4dGlgRVEKmM8MSIv1d8yzdemifVNwXiQJcw5cV97CwBRC/0 uOXFpJetfKs/o+EOfHtTvzyc8T0KEQRj48yJW0oWYeskHL8AARTH8xL7xigZrRCTxRO5z 4esrw0uFQ8YQlqpU+Hr92lPh2fixG8L8BD+NKd+NkY6NQG1U8tEzdxqnmaH9QIf+thA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793201636; h=Received:DKIM-Signature:Subject:To:Cc:From:Date:Message-ID: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=Qk4WspkjjfezQ4y0FQEzPoRSpjyh5acm0ePtZuLIChw=; b=br8A4GWSTr28JJ9fROBzAgP1/1wpsY6xuUWEieMwOicbcgo6fr4E9r/yIU3Y4VZVmdhN XKnVLV0I6pyjjQzaj8moaStXKeO7KIVD/Yl+iUOU6MiJ5rtZhjIW3ifUzZ4nxERoEySMC WrylvRwCRB0kCeDm4yBRwkmFrP7NiORce4Ia3+RvtJp21Hqev6dkieibev4DAyv8WDCBP sZtvDqTRG+Cd/MLZnpNmBmA/J4esKgbsYofbB6wdZKM2AXx3q50cav4Zg00sGqxD8NBm0 vwhWm7zn+LgwM8P1e/oC7/aSyDjcgI0WIs3n2fX2pkiwj/knr6t4f3JHJwgXqvf+Tyw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=A31CILZT; 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 6577D606A31F for ; Wed, 28 Oct 2026 15:33:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=A31CILZT Received: by smtp.kernel.org (Postfix) with ESMTPSA id AA4C41F01825; Wed, 28 Oct 2026 15:33:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793201636; bh=Qk4WspkjjfezQ4y0FQEzPoRSpjyh5acm0ePtZuLIChw=; h=Subject:To:Cc:From:Date; b=A31CILZTt9hKDpaLPx+SlwoKqpdRZNaYFmnbmr7vFTcUiDWn68Xh2vgzwEjcHaa4b 909BoSEgDVPaFaH1YhkcNql5ZKZvU6l8dDvfjhwAoIXDkf2jJVOx0qvcI29cUbrqK4 MjDUUYO0UnGSjHRVBOHHG/OupbojFGYS6LDB+fAI= Subject: FAILED: patch "[PATCH] fork: don't create io threads once PF_POSTCOREDUMP is set" failed to apply to 6.12-stable tree To: brauner@kernel.org,oleg@redhat.com Cc: From: Date: Wed, 28 Oct 2026 16:33:50 +0100 Message-ID: <2026102850-unleveled-version-e04b@gregkh> 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-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.12-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y git checkout FETCH_HEAD git cherry-pick -x 1f978881ce6c9ac4f4d4a7b6a6e52339eadcd350 # git commit -s git send-email --to '' --in-reply-to '2026102850-unleveled-version-e04b@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 1f978881ce6c9ac4f4d4a7b6a6e52339eadcd350 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Mon, 21 Sep 2026 15:45:03 +0200 Subject: [PATCH] fork: don't create io threads once PF_POSTCOREDUMP is set 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) diff --git a/kernel/fork.c b/kernel/fork.c index 0489d11656d9..623eaead3747 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2700,8 +2700,8 @@ 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);