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=1793212536; b=jN8mha44TxJdLN7ILqqtTTFkojePms4z3f/gx6Y9rAFlMBbCktpc5eCjzg70AAII8z0r 0TVCbmk/3/DayKadyZRilxnkPodIyaNIVRp03NWcUmp2iTJASN6C1ZBoncKqlA6cG9xW6 HEJfFLZlTFkzCWIdFL/33uPCNDDkJ7m1yhKSDvGWLbR8A9ExGyqBsnlkJ90QECEXTTL7C Otr0eTizhG24A+HseJOmW9dsTU/2tsXFLf7Cq2WIJNtr63606SZlNYp9SgQ5OrvGjjtTS mTChfCAaSgFN4Y2BT/N+IyfiLY6hrm98LXmugNCJnK5qxEtxSMVA/ZBHdHTdIfSbmmw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793212536; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=g8+4NrYDBU88KvziQw6ngguJNluZCOX67INal4Z+q3w=; b=LVbSu+mdiVDRn0muZxJi11XhWw2BMYLOrMaCGang37hukFHKmSGab2Hxudj4hlVG1Gpu 7snOS55F4bCSHRsqT9h3bz9RK1HE87pDMn85GxpUGLSG3NJ0SHmnahMdh142WvuJ7NBUe jw1xS6rZrYP2+pzvfMwvfUa9J+v5nVqxlwQm7gP0b9iSiET8YQOa6U9jFZZVVgxaFfB9j OugEnbXK1UR6GfawzKD/9I6fB0fwLjKpsi22resdosPn2VCV8srkHJY7g9mSe0B8Xpb27 txfiIKW3mH5YSBqZBQaxPvxCqq8QzmYigf3fn8q9hnMyD19ES76pPHheN0VYAtlNA2w== 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="GcjymOI/"; 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 C21F9606A31E for ; Wed, 28 Oct 2026 18:35:35 +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=GcjymOI/ Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2685D1F031E0; Wed, 28 Oct 2026 18:35:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793212535; bh=g8+4NrYDBU88KvziQw6ngguJNluZCOX67INal4Z+q3w=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=GcjymOI/amBGe5Rf38p3gwsfn/XlGFZ5/izGSl9lRctfu/4hPu0SUTT77hjHaetDj 9TaOB+dF2HWxj9JBIgmiqwVTmnjr5dRj1zuSCGGyH7pnZGey0KRqib138x7s3jCE4Z bfURZP7mcN2VDWmfObaQqA05yd7zEPN7gRybkCbm6eamVtrFpOetRP3fUImIpHs7NB 9SEkZh2QTkhMFBMF/ftTcB+7VCPUlUSlrQB1sX7jAbNuIOZgPnxDAa0RpFC2G/zvN3 zIelrnp+KpdQc+4nEV6R6tsjv1i+mQObGYSy3QW8FOeNA/8Z5XRS9JzOJuLA71WYti UxAa5Wfc8UYfg== From: Sasha Levin To: stable@vger.kernel.org Cc: Christian Brauner , Oleg Nesterov , Sasha Levin Subject: [PATCH 6.18.y 2/2] fork: don't create io threads once PF_POSTCOREDUMP is set Date: Wed, 28 Oct 2026 14:35:33 -0400 Message-ID: <20261028183505.1719907-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261028183505.1719907-1-sashal@kernel.org> References: <2026102850-pulverize-satin-96a4@gregkh> <20261028183505.1719907-1-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 bf0bbd8a569e5..b7543a93f269a 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2559,8 +2559,8 @@ 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