[PATCH 5.13 019/151] io_uring: fix ctx-exit io_rsrc_put_work() deadlock

Greg Kroah-Hartman
2021-08-16T13:19:57Z

From: Pavel Begunkov <asml.silence@gmail.com>

commit 43597aac1f87230cb565ab354d331682f13d3c7a upstream.

__io_rsrc_put_work() might need ->uring_lock, so nobody should wait for
rsrc nodes holding the mutex. However, that's exactly what
io_ring_ctx_free() does with io_wait_rsrc_data().

Split it into rsrc wait + dealloc, and move the first one out of the
lock.

Cc: stable@vger.kernel.org
Fixes: b60c8dce33895 ("io_uring: preparation for rsrc tagging")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/0130c5c2693468173ec1afab714e0885d2c9c363.1628559783.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/io_uring.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8614,13 +8614,10 @@ static void io_req_caches_free(struct io
mutex_unlock(&ctx->uring_lock);
}

-static bool io_wait_rsrc_data(struct io_rsrc_data *data)
+static void io_wait_rsrc_data(struct io_rsrc_data *data)
{
- if (!data)
- return false;
- if (!atomic_dec_and_test(&data->refs))
+ if (data && !atomic_dec_and_test(&data->refs))
wait_for_completion(&data->done);
- return true;
}

static void io_ring_ctx_free(struct io_ring_ctx *ctx)
@@ -8632,10 +8629,14 @@ static void io_ring_ctx_free(struct io_r
ctx->mm_account = NULL;
}

+ /* __io_rsrc_put_work() may need uring_lock to progress, wait w/o it */
+ io_wait_rsrc_data(ctx->buf_data);
+ io_wait_rsrc_data(ctx->file_data);
+
mutex_lock(&ctx->uring_lock);
- if (io_wait_rsrc_data(ctx->buf_data))
+ if (ctx->buf_data)
__io_sqe_buffers_unregister(ctx);
- if (io_wait_rsrc_data(ctx->file_data))
+ if (ctx->file_data)
__io_sqe_files_unregister(ctx);
if (ctx->rings)
__io_cqring_overflow_flush(ctx, true);