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=1793212519; b=Yk//RDApvYduv9I1hzjpvKX5XQpk2AJcu21qpADaO7mYRme2qp5dHds2zrc/JVYWXCSG x2E2GwRWwxD+6Kx/YC2Kl8xYDgCU3pVKN+dsZjVZEfFCthLIPXJetD2rSjOg6fTNtPHG0 8asMEZuSqvVoPDcoCTl99jpinL4Y9MFH/+ha2Y6aiYsyGnpT80LM6tgPFZ1GhI2LiZMBN 9AocTeN6rZmsmWbJKo4fi0OGeA+/QsrR/4t4/e6Ob6NE7wwi3stNE2t9uE/Gk9yZXwyNY biISSIa06H1mHD4NXk7Tg+C0zZwuftT2QPtuyu0Ec5h5vIA3WTuapw5h+mEduT//WKw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793212519; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=rVb6hAD/54DYNjEeuOXpuBsBpH6T2qGeIYMqAnBgfSk=; b=rQD8U6p2Q5XFKALD4OxXnFiBbCiAaRRbfqrGHppxBYhRruWbfXkBfmGQ2xvL5G+cz2b3 uSVXIMjQ9anhH/mirZUKRONJ5v4OxCtPvgYF+JkDHR0xn3XYUtqLHg6xiodgEZscxbHSS A83l7lu+K4S5OG6RzrZR3uqJRHyUUAxTu2zcWYpHsJ0AcB+c6s4EV3U7aw8WeMK2muTkK EvCsj7+oUoa2voKGNFP4ocwwtEi6SsA5EmLGm9THXeGtsOkU9A+w0RGfNFlsbV/5Rx4MP 6tfjFHPHYISBDMRCKvdygdTAalgsBXkM84rgnK7jDUEMqJIbP+UQ4aX1fiaieW6Zzaw== 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=KUozNoh3; 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 8DC61606A31E for ; Wed, 28 Oct 2026 18:35:19 +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=KUozNoh3 Received: by smtp.kernel.org (Postfix) with ESMTPSA id DFD4F1F01825; Wed, 28 Oct 2026 18:35:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793212519; bh=rVb6hAD/54DYNjEeuOXpuBsBpH6T2qGeIYMqAnBgfSk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=KUozNoh3DhaRvpHqAlzdUdnDE1tSZfSiOt7tH7RDf4DphPgKJD2G+FThQwCBUfsu4 lNdUaAsl65Z0M12yYBBihv29CCM1xisEBvt32nFRnwICTwpIxq/ucJd6SMR5TDkMM1 N6Xpsp4ce75pyc1glrNjnNlu+t4bmQ2xDBIZH6me46bWJm4pI0cagAhZ1vczLgKgHN n6aXHuDHhKQRrczlg2SuKRYVUz0UoeLJSBPkfa1bVhIUlFHnyWhsvtauAHBYPFho8m BxTvWmsZGTCdYOODXEZuZ4G+lewRkdvGOXAJzFwvovdcT59Z6vRTGzDwDfshaC+8Dz Yt4BfV8O75N6A== From: Sasha Levin To: stable@vger.kernel.org Cc: Christian Brauner , Chris Mason , Sasha Levin Subject: [PATCH 6.6.y 2/2] fork: release the files of a failed fork after sched_cancel_fork() Date: Wed, 28 Oct 2026 14:35:16 -0400 Message-ID: <20261028183504.1718588-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261028183504.1718588-1-sashal@kernel.org> References: <2026102801-startle-saddled-529f@gregkh> <20261028183504.1718588-1-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 296a98c1fa50778c3b31eebed1a3f903f9684349 ] Reorder copy_process() cleanup so sched_fork() taking scx_fork_rwsem scx_pre_fork() is safe and isn't held around exiting files. Right now, a fork that fails while another thread closed the bpf link fd will deadlock against its own read side. It also blocks every fork on the system: copy_process() holds scx_fork_rwsem for read exit_files() close_files() filp_close_sync() bpf_scx_unreg() kthread_flush_work() waits for the disable work scx_root_disable() percpu_down_write(&scx_fork_rwsem) Simply release the child's files after sched_cancel_fork() dropped the lock. The task starts out as a copy of its parent so p->files points to the parent's table until copy_files() replaces it. exit_files() must not run for a fork that failed before that. Clear p->files up front so exit_files() is a no-op for those and make copy_files() set it explicitly for CLONE_FILES. Reported-by: Chris Mason Link: https://patch.msgid.link/20260921-work-coredump-fixes-v3-7-8e4adb1619e6@kernel.org Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Sasha Levin --- kernel/fork.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 7d5ec03d7caca..88315fdd8f847 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1799,6 +1799,7 @@ static int copy_files(unsigned long clone_flags, struct task_struct *tsk, if (clone_flags & CLONE_FILES) { atomic_inc(&oldf->count); + tsk->files = oldf; return 0; } @@ -2401,6 +2402,8 @@ __latent_entropy struct task_struct *copy_process( INIT_LIST_HEAD(&p->sibling); rcu_copy_process(p); p->vfork_done = NULL; + /* Set by copy_files(), exit_files() on the error path skips NULL. */ + p->files = NULL; spin_lock_init(&p->alloc_lock); init_sigpending(&p->pending); @@ -2503,7 +2506,7 @@ __latent_entropy struct task_struct *copy_process( goto bad_fork_cleanup_semundo; retval = copy_fs(clone_flags, p); if (retval) - goto bad_fork_cleanup_files; + goto bad_fork_cleanup_semundo; retval = copy_sighand(clone_flags, p); if (retval) goto bad_fork_cleanup_fs; @@ -2782,8 +2785,6 @@ __latent_entropy struct task_struct *copy_process( __cleanup_sighand(p->sighand); bad_fork_cleanup_fs: exit_fs(p); /* blocking */ -bad_fork_cleanup_files: - exit_files(p); /* blocking */ bad_fork_cleanup_semundo: exit_sem(p); bad_fork_cleanup_security: @@ -2794,6 +2795,8 @@ __latent_entropy struct task_struct *copy_process( perf_event_free_task(p); bad_fork_sched_cancel_fork: sched_cancel_fork(p); + /* ->release() of a file may need scx_fork_rwsem for write. */ + exit_files(p); /* blocking */ bad_fork_cleanup_policy: lockdep_free_task(p); #ifdef CONFIG_NUMA -- 2.53.0