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io_uring: fix complete_post use ctx after free 

If io_req_complete_post() put not a final ref, we can't rely on the
request's ctx ref, and so ctx may potentially be freed while
complete_post() is in io_cqring_ev_posted()/etc.

In that case get an additional ctx reference, and put it in the end, so
protecting following io_cqring_ev_posted(). And also prolong ctx
lifetime until spin_unlock happens, as we do with mutexes, so added
percpu_ref_get() doesn't race with ctx free.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2021-03-14 20:57:09 +00:00 committed by Jens Axboe
parent efe814a471
commit 180f829fe4
1 changed files with 11 additions and 6 deletions
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17
fs/io_uring.c
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@ -1550,14 +1550,17 @@ static void io_req_complete_post(struct io_kiocb *req, long res,
io_put_task(req->task, 1);
list_add(&req->compl.list, &cs->locked_free_list);
cs->locked_free_nr++;
} else
req = NULL;
} else {
if (!percpu_ref_tryget(&ctx->refs))
req = NULL;
}
io_commit_cqring(ctx);
spin_unlock_irqrestore(&ctx->completion_lock, flags);
io_cqring_ev_posted(ctx);
if (req)
if (req) {
io_cqring_ev_posted(ctx);
percpu_ref_put(&ctx->refs);
}
}
static void io_req_complete_state(struct io_kiocb *req, long res,
@ -8373,11 +8376,13 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
{
/*
* Some may use context even when all refs and requests have been put,
* and they are free to do so while still holding uring_lock, see
* __io_req_task_submit(). Wait for them to finish.
* and they are free to do so while still holding uring_lock or
* completion_lock, see __io_req_task_submit(). Wait for them to finish.
*/
mutex_lock(&ctx->uring_lock);
mutex_unlock(&ctx->uring_lock);
spin_lock_irq(&ctx->completion_lock);
spin_unlock_irq(&ctx->completion_lock);
io_sq_thread_finish(ctx);
io_sqe_buffers_unregister(ctx);