Kernel/linux-next
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git synced 2024-12-29 09:12:07 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

io_uring: fix mutex_unlock with unreferenced ctx

Browse Source 
Callers of mutex_unlock() have to make sure that the mutex stays alive
for the whole duration of the function call. For io_uring that means
that the following pattern is not valid unless we ensure that the
context outlives the mutex_unlock() call.

mutex_lock(&ctx->uring_lock);
req_put(req); // typically via io_req_task_submit()
mutex_unlock(&ctx->uring_lock);

Most contexts are fine: io-wq pins requests, syscalls hold the file,
task works are taking ctx references and so on. However, the task work
fallback path doesn't follow the rule.

Cc:  <stable@vger.kernel.org>
Fixes: 04fc6c802d ("io_uring: save ctx put/get for task_work submit")
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/io-uring/CAG48ez3xSoYb+45f1RLtktROJrpiDQ1otNvdR+YLQf7m+Krj5Q@mail.gmail.com/
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2023-12-03 15:37:53 +00:00 committed by Jens Axboe
parent 73363c262d
commit f7b32e7850
1 changed files with 3 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
io_uring/io_uring.c
View File

@ -271,6 +271,7 @@ static __cold void io_fallback_req_func(struct work_struct *work)
struct io_kiocb *req, *tmp;
struct io_tw_state ts = { .locked = true, };
percpu_ref_get(&ctx->refs);
mutex_lock(&ctx->uring_lock);
llist_for_each_entry_safe(req, tmp, node, io_task_work.node)
req->io_task_work.func(req, &ts);
@ -278,6 +279,7 @@ static __cold void io_fallback_req_func(struct work_struct *work)
return;
io_submit_flush_completions(ctx);
mutex_unlock(&ctx->uring_lock);
percpu_ref_put(&ctx->refs);
}
static int io_alloc_hash_table(struct io_hash_table *table, unsigned bits)
@ -3146,12 +3148,7 @@ static __cold void io_ring_exit_work(struct work_struct *work)
init_completion(&exit.completion);
init_task_work(&exit.task_work, io_tctx_exit_cb);
exit.ctx = ctx;
/*
* Some may use context even when all refs and requests have been put,
* and they are free to do so while still holding uring_lock or
* completion_lock, see io_req_task_submit(). Apart from other work,
* this lock/unlock section also waits them to finish.
*/
mutex_lock(&ctx->uring_lock);
while (!list_empty(&ctx->tctx_list)) {
WARN_ON_ONCE(time_after(jiffies, timeout));