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 <haoxu@linux.alibaba.com>
Link: https://lore.kernel.org/r/20210820221954.61815-1-haoxu@linux.alibaba.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5d3df4f..706ac8c 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);
