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| author | Pavel Begunkov <asml.silence@gmail.com> | 2023-12-03 15:37:53 +0000 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2023-12-03 19:09:28 -0700 |
| commit | f7b32e785042d2357c5abc23ca6db1b92c91a070 (patch) | |
| tree | 0a06a82fbfd4f58f40b49ba689d1c5aa43ca4aa3 /io_uring | |
| parent | 73363c262d6a7d26063da96610f61baf69a70f7c (diff) | |
| download | lwn-f7b32e785042d2357c5abc23ca6db1b92c91a070.tar.gz lwn-f7b32e785042d2357c5abc23ca6db1b92c91a070.zip | |
io_uring: fix mutex_unlock with unreferenced ctx
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>
Diffstat (limited to 'io_uring')
| -rw-r--r-- | io_uring/io_uring.c | 9 |
1 files changed, 3 insertions, 6 deletions
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index aba5657d287e..9626a363f121 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -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)); |