data race but introduced a possible deadlock and inconsistentcy in irq
states. E.g.
io_poll_remove_all()
spin_lock_irq(timeout_lock)
io_poll_remove_one()
spin_lock/unlock_irq(poll_lock);
spin_unlock_irq(timeout_lock)
Another type of problem is freeing a request while holding
->timeout_lock, which may leads to a deadlock in
io_commit_cqring() -> io_flush_timeouts() and other places.
Having 3 nested locks is also too ugly. Add io_match_task_safe(), which
would briefly take and release timeout_lock for race prevention inside,
so the actuall request cancellation / free / etc. code doesn't have it
taken.
Reported-by: syzbot+ff49a3059d49b0ca0eec@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+847f02ec20a6609a328b@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+3368aadcd30425ceb53b@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+51ce8887cdef77c9ac83@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+3cb756a49d2f394a9ee3@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 674ee8e1b4a41 ("io_uring: correct link-list traversal locking")
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
fs/io_uring.c | 60 +++++++++++++++++++++++++++++++++++----------------
1 file changed, 42 insertions(+), 18 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 7dd112d44adf..75841b919dce 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1278,6 +1278,7 @@ static void io_refs_resurrect(struct percpu_ref *ref, struct completion *compl)
static bool io_match_task(struct io_kiocb *head, struct task_struct *task,
bool cancel_all)
+ __must_hold(&req->ctx->timeout_lock)
{
struct io_kiocb *req;
@@ -1293,6 +1294,44 @@ static bool io_match_task(struct io_kiocb *head, struct task_struct *task,
return false;
}
+static bool io_match_linked(struct io_kiocb *head)
+{
+ struct io_kiocb *req;
+
+ io_for_each_link(req, head) {
+ if (req->flags & REQ_F_INFLIGHT)
+ return true;
+ }
+ return false;
+}
+
+/*
+ * As io_match_task() but protected against racing with linked timeouts.
+ * User must not hold timeout_lock.
+ */
+static bool io_match_task_safe(struct io_kiocb *head, struct task_struct *task,
+ bool cancel_all)
+{
+ bool matched;
+
+ if (task && head->task != task)
+ return false;
+ if (cancel_all)
+ return true;
+
+ if (head->flags & REQ_F_LINK_TIMEOUT) {
+ struct io_ring_ctx *ctx = head->ctx;
+
+ /* protect against races with linked timeouts */
+ spin_lock_irq(&ctx->timeout_lock);
+ matched = io_match_linked(head);
+ spin_unlock_irq(&ctx->timeout_lock);
+ } else {
+ matched = io_match_linked(head);
+ }
+ return matched;
+}
+
static inline bool req_has_async_data(struct io_kiocb *req)
{
return req->flags & REQ_F_ASYNC_DATA;
@@ -5699,17 +5738,15 @@ static __cold bool io_poll_remove_all(struct io_ring_ctx *ctx,
int posted = 0, i;
spin_lock(&ctx->completion_lock);
- spin_lock_irq(&ctx->timeout_lock);
for (i = 0; i < (1U << ctx->cancel_hash_bits); i++) {
struct hlist_head *list;
list = &ctx->cancel_hash[i];
hlist_for_each_entry_safe(req, tmp, list, hash_node) {
- if (io_match_task(req, tsk, cancel_all))
+ if (io_match_task_safe(req, tsk, cancel_all))
posted += io_poll_remove_one(req);
}
}
- spin_unlock_irq(&ctx->timeout_lock);
spin_unlock(&ctx->completion_lock);
if (posted)
@@ -9565,19 +9602,8 @@ static bool io_cancel_task_cb(struct io_wq_work *work, void *data)
{
struct io_kiocb *req = container_of(work, struct io_kiocb, work);
struct io_task_cancel *cancel = data;
- bool ret;
- if (!cancel->all && (req->flags & REQ_F_LINK_TIMEOUT)) {
- struct io_ring_ctx *ctx = req->ctx;
-
- /* protect against races with linked timeouts */
- spin_lock_irq(&ctx->timeout_lock);
- ret = io_match_task(req, cancel->task, cancel->all);
- spin_unlock_irq(&ctx->timeout_lock);
- } else {
- ret = io_match_task(req, cancel->task, cancel->all);
- }
- return ret;
+ return io_match_task_safe(req, cancel->task, cancel->all);
}
static __cold bool io_cancel_defer_files(struct io_ring_ctx *ctx,
@@ -9588,14 +9614,12 @@ static __cold bool io_cancel_defer_files(struct io_ring_ctx *ctx,
LIST_HEAD(list);
spin_lock(&ctx->completion_lock);
- spin_lock_irq(&ctx->timeout_lock);
list_for_each_entry_reverse(de, &ctx->defer_list, list) {
- if (io_match_task(de->req, task, cancel_all)) {
+ if (io_match_task_safe(de->req, task, cancel_all)) {
list_cut_position(&list, &ctx->defer_list, &de->list);
break;
}
}
- spin_unlock_irq(&ctx->timeout_lock);
spin_unlock(&ctx->completion_lock);
if (list_empty(&list))
return false;
