From 296a98c1fa50778c3b31eebed1a3f903f9684349 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Mon, 21 Sep 2026 15:44:56 +0200 Subject: [PATCH] fork: release the files of a failed fork after sched_cancel_fork() 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) --- 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