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=1793826788; b=Q4eWFX4ppe5C4p8MTtJOyGKk9BCdFXZVdtEB23uDWvfgQmo+In2/ZTNJ9hO3zvkvqW8z /UlJLHejQART2XmHSZfGbJ1qzfF++jc9ogBoiUujjRmUl4TlB9AKzcf+U6XI6MYlLNjOX fCibesrfm2wImfMsLZ/NHnSVxMjCoRlxL9gFsefqW8fJAxzHF41H14tQVWauXhDsj42Zj XutFsJaPV0k6iPAoOI1UvbGRDA5dq5ui5f3PQyznQ+Poa4FM2Q8X1j5aG1wwDrJneoiJ2 0jXMTO7UWrJviVqtHVSOI94ofAymgN0sMAQB5iSyjwv57yYOTMOfaNa9xS66Jx4qi9w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793826788; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=up85Q/94prZ9tdlI1vWxiuTF31Yl8hNJygqcEtuSWj4=; b=P5QGVDHQImFcWKUwKE/yld3LaRn1eeDzDcLFuRWl2YDrTjWEOSaFp94DEh90B/gAuTxW XpOKRzX2XyVmrIwzJDKQDpjfyI0Gn7ohnn0oZnn/ZIC63KXpUjk5jg4e83J3TBJky5Q+S 9sw/LaR/tDEuntXXpypTjFaMDOD84DtGfkQUmkvObnwZtuGSk9UrVZzeGVCWo8X6QisFm wFQ29clJQ2LyjRyarM4tJH4GGqCdbhvpz4np4YVVwkzBZ36m9m84wjzweqag8f5L3WUmJ B64wnZHlwfYuHNN8k/vgI7K/Zke52ynqQcgb6ablKjvb1s00s8ZlItbvZF/zKiDWqCA== 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=1ioER5P1; 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 52F576071A07; Wed, 4 Nov 2026 21:13:08 +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=1ioER5P1 Received: by smtp.kernel.org (Postfix) with ESMTPSA id A00371F00919; Wed, 4 Nov 2026 21:13:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793826787; bh=up85Q/94prZ9tdlI1vWxiuTF31Yl8hNJygqcEtuSWj4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=1ioER5P12vsX9oyP5FRqeIKufGt0Mo8PWBO5mO0DZM7GCDKhXMGyk1PLovqfH+PpT PEs3MKFS3+wtLDCrHXwyyrU9iByXchHxEytiHRtQbmpnGOcMlyYjrBYQqppu1haU4k jNTbNw2N0Bcr2tzAmtJWVTfJJcIMOl+udvlzLj2Y= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Oleg Nesterov , "Christian Brauner (Amutable)" , Sasha Levin Subject: [PATCH 6.18 0010/1005] fork: dont create io threads once PF_POSTCOREDUMP is set Date: Wed, 4 Nov 2026 15:55:43 -0500 Message-ID: <20261104211043.824067510@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261104211043.516122098@linuxfoundation.org> References: <20261104211043.516122098@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ 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