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io_uring: close a small race gap for files cancel

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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: 0f2122045b ("io_uring: don't rely on weak ->files references")
Cc: <stable@vger.kernel.org> # 5.5+
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2020-12-18 13:12:21 +00:00 committed by Jens Axboe
parent 0020ef04e4
commit dfea9fce29
1 changed files with 6 additions and 6 deletions
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12
fs/io_uring.c
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@ -6098,15 +6098,15 @@ static void io_req_drop_files(struct io_kiocb *req)
struct io_uring_task *tctx = req->task->io_uring;
unsigned long flags;
spin_lock_irqsave(&ctx->inflight_lock, flags);
list_del(&req->inflight_entry);
if (atomic_read(&tctx->in_idle))
wake_up(&tctx->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);
spin_lock_irqsave(&ctx->inflight_lock, flags);
list_del(&req->inflight_entry);
spin_unlock_irqrestore(&ctx->inflight_lock, flags);
req->flags &= ~REQ_F_INFLIGHT;
req->work.flags &= ~IO_WQ_WORK_FILES;
if (atomic_read(&tctx->in_idle))
wake_up(&tctx->wait);
}
static void __io_clean_op(struct io_kiocb *req)