From 99c8bc52d1321ab3a711eba2941eadbe7425230f Mon Sep 17 00:00:00 2001 From: Hao Xu Date: Sat, 21 Aug 2021 06:19:54 +0800 Subject: [PATCH] io_uring: fix lack of protection for compl_nr coml_nr in ctx_flush_and_put() is not protected by uring_lock, this may cause problems when accessing in parallel: say coml_nr > 0 ctx_flush_and put other context if (compl_nr) get mutex coml_nr > 0 do flush coml_nr = 0 release mutex get mutex do flush (*) release mutex in (*) place, we call io_cqring_ev_posted() and users likely get no events there. To avoid spurious events, re-check the value when under the lock. Fixes: 2c32395d8111 ("io_uring: fix __tctx_task_work() ctx race") Signed-off-by: Hao Xu Link: https://lore.kernel.org/r/20210820221954.61815-1-haoxu@linux.alibaba.com Signed-off-by: Jens Axboe --- fs/io_uring.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index 5d3df4f913a8..706ac8c03b95 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -2007,7 +2007,8 @@ static void ctx_flush_and_put(struct io_ring_ctx *ctx) return; if (ctx->submit_state.compl_nr) { mutex_lock(&ctx->uring_lock); - io_submit_flush_completions(ctx); + if (ctx->submit_state.compl_nr) + io_submit_flush_completions(ctx); mutex_unlock(&ctx->uring_lock); } percpu_ref_put(&ctx->refs);