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io_uring: fix link traversal locking

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WARNING: inconsistent lock state
5.16.0-rc2-syzkaller #0 Not tainted
inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
ffff888078e11418 (&ctx->timeout_lock
){?.+.}-{2:2}
, at: io_timeout_fn+0x6f/0x360 fs/io_uring.c:5943
{HARDIRQ-ON-W} state was registered at:
  [...]
  spin_unlock_irq include/linux/spinlock.h:399 [inline]
  __io_poll_remove_one fs/io_uring.c:5669 [inline]
  __io_poll_remove_one fs/io_uring.c:5654 [inline]
  io_poll_remove_one+0x236/0x870 fs/io_uring.c:5680
  io_poll_remove_all+0x1af/0x235 fs/io_uring.c:5709
  io_ring_ctx_wait_and_kill+0x1cc/0x322 fs/io_uring.c:9534
  io_uring_release+0x42/0x46 fs/io_uring.c:9554
  __fput+0x286/0x9f0 fs/file_table.c:280
  task_work_run+0xdd/0x1a0 kernel/task_work.c:164
  exit_task_work include/linux/task_work.h:32 [inline]
  do_exit+0xc14/0x2b40 kernel/exit.c:832

674ee8e1b4 ("io_uring: correct link-list traversal locking") fixed a
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@syzkaller.appspotmail.com
Reported-by: syzbot+847f02ec20a6609a328b@syzkaller.appspotmail.com
Reported-by: syzbot+3368aadcd30425ceb53b@syzkaller.appspotmail.com
Reported-by: syzbot+51ce8887cdef77c9ac83@syzkaller.appspotmail.com
Reported-by: syzbot+3cb756a49d2f394a9ee3@syzkaller.appspotmail.com
Fixes: 674ee8e1b4 ("io_uring: correct link-list traversal locking")
Cc: stable@kernel.org # 5.15+
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/397f7ebf3f4171f1abe41f708ac1ecb5766f0b68.1637937097.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2021-11-26 14:38:15 +00:00 committed by Jens Axboe
parent 617a89484d
commit 6af3f48bf6
1 changed files with 42 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

60
fs/io_uring.c
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@ -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;