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io_uring: only call io_cqring_ev_posted() if events were posted 

This normally doesn't cause any extra harm, but it does mean that we'll
increment the eventfd notification count, if one has been registered
with the ring. This can confuse applications, when they see more
notifications on the eventfd side than are available in the ring.

Do the nice thing and only increment this count, if we actually posted
(or even overflowed) events.

Reported-and-tested-by: Dan Melnic <dmm@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2021-01-24 16:58:56 -07:00
parent 84965ff8a8
commit b18032bb0a
1 changed files with 7 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
fs/io_uring.c
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@ -1779,12 +1779,13 @@ static bool __io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force,
struct io_kiocb *req, *tmp;
struct io_uring_cqe *cqe;
unsigned long flags;
bool all_flushed;
bool all_flushed, posted;
LIST_HEAD(list);
if (!force && __io_cqring_events(ctx) == rings->cq_ring_entries)
return false;
posted = false;
spin_lock_irqsave(&ctx->completion_lock, flags);
list_for_each_entry_safe(req, tmp, &ctx->cq_overflow_list, compl.list) {
if (!io_match_task(req, tsk, files))
@ -1804,6 +1805,7 @@ static bool __io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force,
WRITE_ONCE(ctx->rings->cq_overflow,
ctx->cached_cq_overflow);
}
posted = true;
}
all_flushed = list_empty(&ctx->cq_overflow_list);
@ -1813,9 +1815,11 @@ static bool __io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force,
ctx->rings->sq_flags &= ~IORING_SQ_CQ_OVERFLOW;
}
io_commit_cqring(ctx);
if (posted)
io_commit_cqring(ctx);
spin_unlock_irqrestore(&ctx->completion_lock, flags);
io_cqring_ev_posted(ctx);
if (posted)
io_cqring_ev_posted(ctx);
while (!list_empty(&list)) {
req = list_first_entry(&list, struct io_kiocb, compl.list);