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=1793201639; b=1TJjVaJuQwwKLouR8dfE2Eturdbaov4G2Nzz+qKfXJtp/8M7JsNSOLvO5969mfsVBFZu /x0ID9IDGj84pa7sBe/JU1e7GI4x/Xorqnzj/oaWXxRQC1pyF1dsd1ixf6NyqLDQEtL87 eR4YKBZH2oh0TECzzMaqoJgR3jUTt8o1Er7X+KfD6/984DXT5X7aA6+sJX0YCk3UBHz4k DmxjmJRzv6eEI1c6hHYIm41xJjVvwJM98HezSgjOc0nh7uwgxc1vsHt7SnWrEfZd2lXP3 QRSjyQLO78942R24DJYvJAd+fOs71fFg4eZTdv+esCPc65Oae7fhHCsd6S5H26EKHDg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793201639; h=Received:DKIM-Signature:Subject:To:Cc:From:Date:Message-ID: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=LOVUEyry4m8xuJjz3vnYyxNR0yzKTLdPrALqR8fEPf8=; b=3gapP9xqDYH1WeqeDWQg8rsYXLu41F3+ekux2n07gjx6Qh0IaUpSDl2qwJo273YZzlmP CG0VbYESTW+GskWBo9sGB1Qj8xO8bwhsG/VS4kO1FZsCoOgiDB/UCCJG1cMgA3N7rQVX5 +mvOCgZQwnQhdVMxHUvisVt5I8s5uc2PVxzdCeLbAIGQNs1ckHwnCMk/yx5kExgdY7wC2 opnNpLNRbkHDZIKWHEsCpj+hEYHRjmKhGxm2sK5JXQ31HMRgX181N68itOM7U1cHI1GVt G2wsnyW1CqiSVzC1JJeffnBoxaH6Rsgv8zjFf3UfpE3vAyja0OZa7JGCaJiatkUd07A== 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=qcnJ3XPo; 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 79B10606A320 for ; Wed, 28 Oct 2026 15:33:59 +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=qcnJ3XPo Received: by smtp.kernel.org (Postfix) with ESMTPSA id 78DE01F01825; Wed, 28 Oct 2026 15:33:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793201639; bh=LOVUEyry4m8xuJjz3vnYyxNR0yzKTLdPrALqR8fEPf8=; h=Subject:To:Cc:From:Date; b=qcnJ3XPoXMaVS3Y2fEhv/qt2kf7sxm2kUvjFcmPxh2NOPTKnuB7RWSZUgHZh1ckA2 eOpG81NqZgnitHtM4VRvkwXEpLC/PmIxY5gnFggMr4NvvgQsJ4TUKM6Ak/ygkl9hEc pFk3NWTsvOTPktjT0C40aEWInXZUmQVuY/xTInxI= Subject: FAILED: patch "[PATCH] fork: don't create io threads once PF_POSTCOREDUMP is set" failed to apply to 6.18-stable tree To: brauner@kernel.org,oleg@redhat.com Cc: From: Date: Wed, 28 Oct 2026 16:33:50 +0100 Message-ID: <2026102850-pulverize-satin-96a4@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 6.18-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-6.18.y git checkout FETCH_HEAD git cherry-pick -x 1f978881ce6c9ac4f4d4a7b6a6e52339eadcd350 # git commit -s git send-email --to '' --in-reply-to '2026102850-pulverize-satin-96a4@gregkh' --subject-prefix 'PATCH 6.18.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);