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This is caused by an AB-BA lock inversion between epoll's ep->mtx and kernfs node teardown. Thread A (epoll_ctl) acquires ep->mtx, then attempts to acquire the kernfs active reference during vfs_poll(). Thread B (kernfs_remove) deactivates the node and attempts to unhook active epoll monitors, which requires ep->mtx. This patch fixes the deadlock by utilizing the existing epoll POLLFREE path. By calling wake_up_pollfree(&on->poll) before the waitqueue is freed, epoll users are notified to detach their wait entries without requiring kernfs teardown to acquire ep->mtx. Reported-by: syzbot+f83fa2cf571bd7650422@syzkaller.appspotmail.com Signed-off-by: Sainath Manda --- fs/kernfs/file.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index 1163aa769..db3fed4d7 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -600,6 +600,14 @@ static void kernfs_unlink_open_file(struct kernfs_node *kn, } if (list_empty(&on->files)) { + /* + * @on->poll is embedded in @on and is about to be freed. Tell + * epoll users to detach their wait entries through the POLLFREE + * callback path before the waitqueue disappears. This path is + * serialized by the waitqueue lock and doesn't require taking + * eventpoll's ep->mtx from kernfs teardown. + */ + wake_up_pollfree(&on->poll); rcu_assign_pointer(kn->attr.open, NULL); kfree_rcu(on, rcu_head); } -- 2.34.1