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io_uring: close a small race gap for files cancel

PATCH In review Pavel Begunkov 2 participants 2 messages Dec 29, 2020 – Dec 30, 2020 1 message not in the archive Stable branch

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Pavel Begunkov

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PATCH 1/1 io_uring: close a small race gap for files cancel

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commit dfea9fce29fda6f2f91161677e0e0d9b671bc099 upstream.

The purpose of io_uring_cancel_files() is to wait for all requests matching ->files to go/be cancelled. We should first drop files of a request in io_req_drop_files() and only then make it undiscoverable for io_uring_cancel_files.

First drop, then delete from list. It's ok to leave req->id->files dangling, because it's not dereferenced by cancellation code, only compared against. It would potentially go to sleep and be awaken by following in io_req_drop_files() wake_up().

Fixes 0f2122045b946 ("io_uring: don't rely on weak ->files references")
Cc <[email protected]> # 5.5+
Signed-off-by Pavel Begunkov <[email protected]>
Signed-off-by Jens Axboe <[email protected]>
---
 fs/io_uring.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
fs/io_uring.c +4 -4
index 86dac2b2e276..dfe33b0b148f 100644
@@ -5854,15 +5854,15 @@ static void io_req_drop_files(struct io_kiocb *req)
 	struct io_ring_ctx *ctx = req->ctx;
 	unsigned long flags;
 
+	put_files_struct(req->work.identity->files);
+	put_nsproxy(req->work.identity->nsproxy);
 	spin_lock_irqsave(&ctx->inflight_lock, flags);
 	list_del(&req->inflight_entry);
-	if (waitqueue_active(&ctx->inflight_wait))
-		wake_up(&ctx->inflight_wait);
 	spin_unlock_irqrestore(&ctx->inflight_lock, flags);
 	req->flags &= ~REQ_F_INFLIGHT;
-	put_files_struct(req->work.identity->files);
-	put_nsproxy(req->work.identity->nsproxy);
 	req->work.flags &= ~IO_WQ_WORK_FILES;
+	if (waitqueue_active(&ctx->inflight_wait))
+		wake_up(&ctx->inflight_wait);
 }
 
 static void __io_clean_op(struct io_kiocb *req)
Signature · 1 line
2.24.0
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#2 lore raw
Quoted 12 lines · Pavel Begunkov

commit dfea9fce29fda6f2f91161677e0e0d9b671bc099 upstream.

The purpose of io_uring_cancel_files() is to wait for all requests matching ->files to go/be cancelled. We should first drop files of a request in io_req_drop_files() and only then make it undiscoverable for io_uring_cancel_files.

First drop, then delete from list. It's ok to leave req->id->files dangling, because it's not dereferenced by cancellation code, only compared against. It would potentially go to sleep and be awaken by following in io_req_drop_files() wake_up().

Quoted 7 lines
Fixes 0f2122045b946 ("io_uring: don't rely on weak ->files references")
Cc <[email protected]> # 5.5+
Signed-off-by Pavel Begunkov <[email protected]>
Signed-off-by Jens Axboe <[email protected]>
---
 fs/io_uring.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Now applied, thanks.

greg k-h