From b76da70fc3759df13e0991706451f1a2e06ba19e Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Wed, 20 Nov 2019 13:05:32 -0700
Subject: [PATCH] io_uring: close lookup gap for dependent next work
When we find new work to process within the work handler, we queue the
linked timeout before we have issued the new work. This can be
problematic for very short timeouts, as we have a window where the new
work isn't visible.
Allow the work handler to store a callback function for this in the work
item, and flag it with IO_WQ_WORK_CB if the caller has done so. If that
is set, then io-wq will call the callback when it has setup the new work
item.
Reported-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
fs/io-wq.c | 3 +++
fs/io-wq.h | 6 +++++-
fs/io_uring.c | 16 ++++++++++++++--
3 files changed, 22 insertions(+), 3 deletions(-)
diff --git a/fs/io-wq.c b/fs/io-wq.c
index b4bc377dda619..9b32b3c811f5a 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -427,6 +427,9 @@ next:
worker->cur_work = work;
spin_unlock_irq(&worker->lock);
+ if (work->flags & IO_WQ_WORK_CB)
+ work->func(&work);
+
if ((work->flags & IO_WQ_WORK_NEEDS_FILES) &&
current->files != work->files) {
task_lock(current);
diff --git a/fs/io-wq.h b/fs/io-wq.h
index 4b29f922f80cf..b68b11bf36331 100644
--- a/fs/io-wq.h
+++ b/fs/io-wq.h
@@ -11,6 +11,7 @@ enum {
IO_WQ_WORK_NEEDS_FILES = 16,
IO_WQ_WORK_UNBOUND = 32,
IO_WQ_WORK_INTERNAL = 64,
+ IO_WQ_WORK_CB = 128,
IO_WQ_HASH_SHIFT = 24, /* upper 8 bits are used for hash key */
};
@@ -22,7 +23,10 @@ enum io_wq_cancel {
};
struct io_wq_work {
- struct list_head list;
+ union {
+ struct list_head list;
+ void *data;
+ };
void (*func)(struct io_wq_work **);
unsigned flags;
struct files_struct *files;
diff --git a/fs/io_uring.c b/fs/io_uring.c
index e9980c584120f..27fefb52910c7 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2679,6 +2679,15 @@ static int __io_submit_sqe(struct io_kiocb *req, struct io_kiocb **nxt,
return 0;
}
+static void io_link_work_cb(struct io_wq_work **workptr)
+{
+ struct io_wq_work *work = *workptr;
+ struct io_kiocb *link = work->data;
+
+ io_queue_linked_timeout(link);
+ work->func = io_wq_submit_work;
+}
+
static void io_wq_submit_work(struct io_wq_work **workptr)
{
struct io_wq_work *work = *workptr;
@@ -2725,8 +2734,11 @@ static void io_wq_submit_work(struct io_wq_work **workptr)
io_prep_async_work(nxt, &link);
*workptr = &nxt->work;
- if (link)
- io_queue_linked_timeout(link);
+ if (link) {
+ nxt->work.flags |= IO_WQ_WORK_CB;
+ nxt->work.func = io_link_work_cb;
+ nxt->work.data = link;
+ }
}
}
--
2.30.2