6.1-stable review patch. If anyone has any objections, please let me know.
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From: Pavel Begunkov asml.silence@gmail.com
commit f7b32e785042d2357c5abc23ca6db1b92c91a070 upstream.
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: stable@vger.kernel.org Fixes: 04fc6c802d ("io_uring: save ctx put/get for task_work submit") Reported-by: Jann Horn jannh@google.com Signed-off-by: Pavel Begunkov asml.silence@gmail.com Link: https://lore.kernel.org/io-uring/CAG48ez3xSoYb+45f1RLtktROJrpiDQ1otNvdR+YLQf... Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- io_uring/io_uring.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-)
--- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -1377,6 +1377,7 @@ static __cold void io_iopoll_try_reap_ev if (!(ctx->flags & IORING_SETUP_IOPOLL)) return;
+ percpu_ref_get(&ctx->refs); mutex_lock(&ctx->uring_lock); while (!wq_list_empty(&ctx->iopoll_list)) { /* let it sleep and repeat later if can't complete a request */ @@ -1394,6 +1395,7 @@ static __cold void io_iopoll_try_reap_ev } } mutex_unlock(&ctx->uring_lock); + percpu_ref_put(&ctx->refs); }
static int io_iopoll_check(struct io_ring_ctx *ctx, long min) @@ -2800,12 +2802,7 @@ static __cold void io_ring_exit_work(str 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));