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b=Pmfck5Q1hr/Yx7jfVeDnT8LVpiwSzMf7eFW7nK93xNMWhIoB5/tzeCrLYo5iu7XAH 89bzw9T7RxA9xAAw0JQjKsvsLeorLNG4KUl3kJRIDmGDFRwloHcDlf/Z1sHk+qmRsj IVhrkt/cFEZuWKGJSGkQ7HTHY7Gs6B58EhjuzYraL7ITnpC2axmVCX9elZ3S4gTSVJ WDbFh5WZdGWNLx+fIZjwamtKYPc1zlH58KlYQV/VowhjiG/OIVAlWQbbI3nHCq9DOj L2lzdtm8snI0OfqWquIVbZV5oy/4xqtz9m15I2WgzsIeSrvLECj91POQTee1+KKCkO rIiO1AoJHW0RA== From: Christian Brauner Date: Mon, 21 Sep 2026 15:44:56 +0200 Subject: [PATCH v3 07/17] fork: release the files of a failed fork after sched_cancel_fork() MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260921-work-coredump-fixes-v3-7-8e4adb1619e6@kernel.org> References: <20260921-work-coredump-fixes-v3-0-8e4adb1619e6@kernel.org> In-Reply-To: <20260921-work-coredump-fixes-v3-0-8e4adb1619e6@kernel.org> To: Oleg Nesterov , Chris Mason , linux-fsdevel@vger.kernel.org Cc: Jens Axboe , Alexander Viro , Jan Kara , NeilBrown , Ingo Molnar , Peter Zijlstra , linux-mm@kvack.org, io-uring@vger.kernel.org, "Christian Brauner (Amutable)" X-Mailer: b4 0.17-dev-db0b7 X-Developer-Signature: v=1; a=openpgp-sha256; l=2806; i=brauner@kernel.org; h=from:subject:message-id; bh=ewDsuLMI5Aha0m3J9gayD6hgJ7X0BeQSbg3MKkl5wZg=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWRtNLlz44ymZcCmDuNsnYhpUV1ZKqHe0Xd5dySxvcmU9 Hf5H7u8o5SFQYyLQVZMkcWh3SRcbjlPxWajTA2YOaxMIEMYuDgFYCKcHAz/DPb4mFvPdHux9MOf zxpzH69pFt/Fls5wT/PZjuRVxh8uvmZk6HhyfUpd8L/PR88an+TZ1vaiXrU1w/qNkozMlP1OwsF PWAA= X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 09CA210000C X-Stat-Signature: 83i8bba1r47ijwxyhm74hd1ig6d4atyd X-Rspam-User: X-HE-Tag: 1789998332-879988 X-HE-Meta: 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 KyMXavpb QOZPXEQUIwY6sWgw2pAB2HFXllSI3FaleKitonM/6lDqCrpv56S+rXLjFcuUrCl0biOe0jrYiciYPaAAwWADf2Z/NGX831ndeMt4fZHWJbgVFabEHJ3tTTB79ClIorsr6etGez918qV9HpwHYVlsvkApgEMRq0CUJF/GaJvbfY30HfCv5ieNFn+zKEFrCbSOMumQUN3zlTtLC6/QyGKfvoKsBA+gw/PufnoEvOrwOuc8Egu0X1wrvD/IVm7xOS8t2ij5hfu1pL4A9n8j2wSEzEkrZPqcwHy+aGmGm Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 Signed-off-by: Christian Brauner (Amutable) --- kernel/fork.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 10be4a0ecb3f..50f5b3e2ca87 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1676,6 +1676,7 @@ static int copy_files(u64 clone_flags, struct task_struct *tsk, if (clone_flags & CLONE_FILES) { atomic_inc(&oldf->count); + tsk->files = oldf; return 0; } @@ -2199,6 +2200,8 @@ __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); @@ -2300,7 +2303,7 @@ __latent_entropy struct task_struct *copy_process( goto bad_fork_cleanup_semundo; retval = copy_fs(clone_flags, p, args->umh); 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; @@ -2613,8 +2616,6 @@ __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: @@ -2625,6 +2626,8 @@ __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