io_uring: defer file table grabbing request cleanup for locked requests
If we're in the error path failing links and we have a link that has
grabbed a reference to the fs_struct, then we cannot safely drop our
reference to the table if we already hold the completion lock. This
adds a hardirq dependency to the fs_struct->lock, which it currently
doesn't have.
Defer the final cleanup and free of such requests to avoid adding this
dependency.
Reported-by: syzbot+ef4b654b49ed7ff049bf@syzkaller.appspotmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 56115cb..5488698 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1108,10 +1108,16 @@ static void __io_commit_cqring(struct io_ring_ctx *ctx)
}
}
-static void io_req_clean_work(struct io_kiocb *req)
+/*
+ * Returns true if we need to defer file table putting. This can only happen
+ * from the error path with REQ_F_COMP_LOCKED set.
+ */
+static bool io_req_clean_work(struct io_kiocb *req)
{
if (!(req->flags & REQ_F_WORK_INITIALIZED))
- return;
+ return false;
+
+ req->flags &= ~REQ_F_WORK_INITIALIZED;
if (req->work.mm) {
mmdrop(req->work.mm);
@@ -1124,6 +1130,9 @@ static void io_req_clean_work(struct io_kiocb *req)
if (req->work.fs) {
struct fs_struct *fs = req->work.fs;
+ if (req->flags & REQ_F_COMP_LOCKED)
+ return true;
+
spin_lock(&req->work.fs->lock);
if (--fs->users)
fs = NULL;
@@ -1132,7 +1141,8 @@ static void io_req_clean_work(struct io_kiocb *req)
free_fs_struct(fs);
req->work.fs = NULL;
}
- req->flags &= ~REQ_F_WORK_INITIALIZED;
+
+ return false;
}
static void io_prep_async_work(struct io_kiocb *req)
@@ -1544,7 +1554,7 @@ static inline void io_put_file(struct io_kiocb *req, struct file *file,
fput(file);
}
-static void io_dismantle_req(struct io_kiocb *req)
+static bool io_dismantle_req(struct io_kiocb *req)
{
io_clean_op(req);
@@ -1552,7 +1562,6 @@ static void io_dismantle_req(struct io_kiocb *req)
kfree(req->io);
if (req->file)
io_put_file(req, req->file, (req->flags & REQ_F_FIXED_FILE));
- io_req_clean_work(req);
if (req->flags & REQ_F_INFLIGHT) {
struct io_ring_ctx *ctx = req->ctx;
@@ -1564,15 +1573,15 @@ static void io_dismantle_req(struct io_kiocb *req)
wake_up(&ctx->inflight_wait);
spin_unlock_irqrestore(&ctx->inflight_lock, flags);
}
+
+ return io_req_clean_work(req);
}
-static void __io_free_req(struct io_kiocb *req)
+static void __io_free_req_finish(struct io_kiocb *req)
{
- struct io_ring_ctx *ctx;
+ struct io_ring_ctx *ctx = req->ctx;
- io_dismantle_req(req);
__io_put_req_task(req);
- ctx = req->ctx;
if (likely(!io_is_fallback_req(req)))
kmem_cache_free(req_cachep, req);
else
@@ -1580,6 +1589,39 @@ static void __io_free_req(struct io_kiocb *req)
percpu_ref_put(&ctx->refs);
}
+static void io_req_task_file_table_put(struct callback_head *cb)
+{
+ struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
+ struct fs_struct *fs = req->work.fs;
+
+ spin_lock(&req->work.fs->lock);
+ if (--fs->users)
+ fs = NULL;
+ spin_unlock(&req->work.fs->lock);
+ if (fs)
+ free_fs_struct(fs);
+ req->work.fs = NULL;
+ __io_free_req_finish(req);
+}
+
+static void __io_free_req(struct io_kiocb *req)
+{
+ if (!io_dismantle_req(req)) {
+ __io_free_req_finish(req);
+ } else {
+ int ret;
+
+ init_task_work(&req->task_work, io_req_task_file_table_put);
+ ret = task_work_add(req->task, &req->task_work, TWA_RESUME);
+ if (unlikely(ret)) {
+ struct task_struct *tsk;
+
+ tsk = io_wq_get_task(req->ctx->io_wq);
+ task_work_add(tsk, &req->task_work, 0);
+ }
+ }
+}
+
static bool io_link_cancel_timeout(struct io_kiocb *req)
{
struct io_ring_ctx *ctx = req->ctx;
@@ -1868,7 +1910,7 @@ static void io_req_free_batch(struct req_batch *rb, struct io_kiocb *req)
req->flags &= ~REQ_F_TASK_PINNED;
}
- io_dismantle_req(req);
+ WARN_ON_ONCE(io_dismantle_req(req));
rb->reqs[rb->to_free++] = req;
if (unlikely(rb->to_free == ARRAY_SIZE(rb->reqs)))
__io_req_free_batch_flush(req->ctx, rb);