From f7b32e785042d2357c5abc23ca6db1b92c91a070 Mon Sep 17 00:00:00 2001 From: Pavel Begunkov Date: Sun, 3 Dec 2023 15:37:53 +0000 Subject: io_uring: fix mutex_unlock with unreferenced ctx Callers of mutex_unlock() have to make sure that the mutex stays alive for the whole duration of the function call. For io_uring that means that the following pattern is not valid unless we ensure that the context outlives the mutex_unlock() call. mutex_lock(&ctx->uring_lock); req_put(req); // typically via io_req_task_submit() mutex_unlock(&ctx->uring_lock); Most contexts are fine: io-wq pins requests, syscalls hold the file, task works are taking ctx references and so on. However, the task work fallback path doesn't follow the rule. Cc: Fixes: 04fc6c802d ("io_uring: save ctx put/get for task_work submit") Reported-by: Jann Horn Signed-off-by: Pavel Begunkov Link: https://lore.kernel.org/io-uring/CAG48ez3xSoYb+45f1RLtktROJrpiDQ1otNvdR+YLQf7m+Krj5Q@mail.gmail.com/ Signed-off-by: Jens Axboe --- io_uring/io_uring.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) (limited to 'io_uring') diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index aba5657d287e..9626a363f121 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -271,6 +271,7 @@ static __cold void io_fallback_req_func(struct work_struct *work) struct io_kiocb *req, *tmp; struct io_tw_state ts = { .locked = true, }; + percpu_ref_get(&ctx->refs); mutex_lock(&ctx->uring_lock); llist_for_each_entry_safe(req, tmp, node, io_task_work.node) req->io_task_work.func(req, &ts); @@ -278,6 +279,7 @@ static __cold void io_fallback_req_func(struct work_struct *work) return; io_submit_flush_completions(ctx); mutex_unlock(&ctx->uring_lock); + percpu_ref_put(&ctx->refs); } static int io_alloc_hash_table(struct io_hash_table *table, unsigned bits) @@ -3146,12 +3148,7 @@ static __cold void io_ring_exit_work(struct work_struct *work) init_completion(&exit.completion); init_task_work(&exit.task_work, io_tctx_exit_cb); exit.ctx = ctx; - /* - * Some may use context even when all refs and requests have been put, - * and they are free to do so while still holding uring_lock or - * completion_lock, see io_req_task_submit(). Apart from other work, - * this lock/unlock section also waits them to finish. - */ + mutex_lock(&ctx->uring_lock); while (!list_empty(&ctx->tctx_list)) { WARN_ON_ONCE(time_after(jiffies, timeout)); -- cgit