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io_uring: fix task_work cap overshooting

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A previous commit fixed task_work overrunning by a lot more than what
the user asked for, by adding a retry list. However, it didn't cap the
overall count, hence for multiple task_work runs inside the same wait
loop, it'd still overshoot the target by potentially a large amount.

Cap it generally inside the wait path. Note that this will still
overshoot the default limit of 20, but should overshoot by no more than
limit-1 in addition to the limit. That still provides a ceiling over how
much task_work will be run, rather than still having gaps where it was
uncapped essentially.

Fixes: f46b9cdb22 ("io_uring: limit local tw done")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2024-11-26 13:42:27 -07:00
parent 0c0a4eae26
commit 49c5c63d48
1 changed files with 19 additions and 15 deletions
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34
io_uring/io_uring.c
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@ -1277,6 +1277,8 @@ static int __io_run_local_work_loop(struct llist_node **node,
struct io_tw_state *ts,
int events)
{
int ret = 0;
while (*node) {
struct llist_node *next = (*node)->next;
struct io_kiocb *req = container_of(*node, struct io_kiocb,
@ -1285,27 +1287,27 @@ static int __io_run_local_work_loop(struct llist_node **node,
io_poll_task_func, io_req_rw_complete,
req, ts);
*node = next;
if (--events <= 0)
if (++ret >= events)
break;
}
return events;
return ret;
}
static int __io_run_local_work(struct io_ring_ctx *ctx, struct io_tw_state *ts,
int min_events)
int min_events, int max_events)
{
struct llist_node *node;
unsigned int loops = 0;
int ret, limit;
int ret = 0;
if (WARN_ON_ONCE(ctx->submitter_task != current))
return -EEXIST;
if (ctx->flags & IORING_SETUP_TASKRUN_FLAG)
atomic_andnot(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);
limit = max(IO_LOCAL_TW_DEFAULT_MAX, min_events);
again:
ret = __io_run_local_work_loop(&ctx->retry_llist.first, ts, limit);
min_events -= ret;
ret = __io_run_local_work_loop(&ctx->retry_llist.first, ts, max_events);
if (ctx->retry_llist.first)
goto retry_done;
@ -1314,11 +1316,10 @@ static int __io_run_local_work(struct io_ring_ctx *ctx, struct io_tw_state *ts,
* running the pending items.
*/
node = llist_reverse_order(llist_del_all(&ctx->work_llist));
ret = __io_run_local_work_loop(&node, ts, ret);
ret += __io_run_local_work_loop(&node, ts, max_events - ret);
ctx->retry_llist.first = node;
loops++;
ret = limit - ret;
if (io_run_local_work_continue(ctx, ret, min_events))
goto again;
retry_done:
@ -1337,16 +1338,18 @@ static inline int io_run_local_work_locked(struct io_ring_ctx *ctx,
if (!io_local_work_pending(ctx))
return 0;
return __io_run_local_work(ctx, &ts, min_events);
return __io_run_local_work(ctx, &ts, min_events,
max(IO_LOCAL_TW_DEFAULT_MAX, min_events));
}
static int io_run_local_work(struct io_ring_ctx *ctx, int min_events)
static int io_run_local_work(struct io_ring_ctx *ctx, int min_events,
int max_events)
{
struct io_tw_state ts = {};
int ret;
mutex_lock(&ctx->uring_lock);
ret = __io_run_local_work(ctx, &ts, min_events);
ret = __io_run_local_work(ctx, &ts, min_events, max_events);
mutex_unlock(&ctx->uring_lock);
return ret;
}
@ -2352,7 +2355,7 @@ int io_run_task_work_sig(struct io_ring_ctx *ctx)
{
if (io_local_work_pending(ctx)) {
__set_current_state(TASK_RUNNING);
if (io_run_local_work(ctx, INT_MAX) > 0)
if (io_run_local_work(ctx, INT_MAX, IO_LOCAL_TW_DEFAULT_MAX) > 0)
return 0;
}
if (io_run_task_work() > 0)
@ -2515,7 +2518,8 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events, u32 flags,
if (!io_allowed_run_tw(ctx))
return -EEXIST;
if (io_local_work_pending(ctx))
io_run_local_work(ctx, min_events);
io_run_local_work(ctx, min_events,
max(IO_LOCAL_TW_DEFAULT_MAX, min_events));
io_run_task_work();
if (unlikely(test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq)))
@ -2586,7 +2590,7 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events, u32 flags,
* now rather than let the caller do another wait loop.
*/
if (io_local_work_pending(ctx))
io_run_local_work(ctx, nr_wait);
io_run_local_work(ctx, nr_wait, nr_wait);
io_run_task_work();
/*
@ -3098,7 +3102,7 @@ static __cold bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
if ((ctx->flags & IORING_SETUP_DEFER_TASKRUN) &&
io_allowed_defer_tw_run(ctx))
ret |= io_run_local_work(ctx, INT_MAX) > 0;
ret |= io_run_local_work(ctx, INT_MAX, INT_MAX) > 0;
ret |= io_cancel_defer_files(ctx, tctx, cancel_all);
mutex_lock(&ctx->uring_lock);
ret |= io_poll_remove_all(ctx, tctx, cancel_all);