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io_uring: don't forget to task-cancel drained reqs 

If there is a long-standing request of one task locking up execution of
deferred requests, and the defer list contains requests of another task
(all files-less), then a potential execution of __io_uring_task_cancel()
by that another task will sleep until that first long-standing request
completion, and that may take long.

E.g.
tsk1: req1/read(empty_pipe) -> tsk2: req(DRAIN)
Then __io_uring_task_cancel(tsk2) waits for req1 completion.

It seems we even can manufacture a complicated case with many tasks
sharing many rings that can lock them forever.

Cancel deferred requests for __io_uring_task_cancel() as well.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2020-11-05 14:06:19 +00:00 committed by Jens Axboe
parent 99b328084f
commit ef9865a442
1 changed files with 8 additions and 2 deletions
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10
fs/io_uring.c
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@ -8496,6 +8496,7 @@ static void io_attempt_cancel(struct io_ring_ctx *ctx, struct io_kiocb *req)
}
static void io_cancel_defer_files(struct io_ring_ctx *ctx,
struct task_struct *task,
struct files_struct *files)
{
struct io_defer_entry *de = NULL;
@ -8503,7 +8504,8 @@ static void io_cancel_defer_files(struct io_ring_ctx *ctx,
spin_lock_irq(&ctx->completion_lock);
list_for_each_entry_reverse(de, &ctx->defer_list, list) {
if (io_match_files(de->req, files)) {
if (io_task_match(de->req, task) &&
io_match_files(de->req, files)) {
list_cut_position(&list, &ctx->defer_list, &de->list);
break;
}
@ -8529,7 +8531,6 @@ static bool io_uring_cancel_files(struct io_ring_ctx *ctx,
if (list_empty_careful(&ctx->inflight_list))
return false;
io_cancel_defer_files(ctx, files);
/* cancel all at once, should be faster than doing it one by one*/
io_wq_cancel_cb(ctx->io_wq, io_wq_files_match, files, true);
@ -8621,6 +8622,11 @@ static void io_uring_cancel_task_requests(struct io_ring_ctx *ctx,
io_sq_thread_park(ctx->sq_data);
}
if (files)
io_cancel_defer_files(ctx, NULL, files);
else
io_cancel_defer_files(ctx, task, NULL);
io_cqring_overflow_flush(ctx, true, task, files);
while (__io_uring_cancel_task_requests(ctx, task, files)) {