Re: [PATCH 1/2] io_uring: add uring_lock as an argument to io_sqe_files_unregister()

Hao Xu
2021-02-04T03:35:25Z

在 2021/2/4 上午12:33, Pavel Begunkov 写道:
> On 03/02/2021 14:57, Hao Xu wrote:
>> io_sqe_files_unregister is currently called from several places:
>> - syscall io_uring_register (with uring_lock)
>> - io_ring_ctx_wait_and_kill() (without uring_lock)
>>
>> There is a AA type deadlock in io_sqe_files_unregister(), thus we need
>> to know if we hold uring_lock in io_sqe_files_unregister() to fix the
>> issue.
>
> It's ugly, just take the lock and kill the patch. There can't be any
> contention during io_ring_ctx_free anyway.
Hi Pavel, I don't get it, do you mean this patch isn't needed, and we
can just unlock(&uring_lock) before io_run_task_work_sig() and
lock(&uring_lock) after it? I knew there won't be contention during
io_ring_ctx_free that's why there is no uring_lock in it.
I tried to just do unlock(&uring_lock) before io_run_task_sig() without
if(locked) check, it reports something like "there are unpaired mutex
lock/unlock" since we cannot just unlock if it's from io_ring_ctx_free.
>
>>
>> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
>> ---
>> fs/io_uring.c | 10 +++++-----
>> 1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index 38c6cbe1ab38..efb6d02fea6f 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -7339,7 +7339,7 @@ static void io_sqe_files_set_node(struct fixed_file_data *file_data,
>> percpu_ref_get(&file_data->refs);
>> }
>>
>> -static int io_sqe_files_unregister(struct io_ring_ctx *ctx)
>> +static int io_sqe_files_unregister(struct io_ring_ctx *ctx, bool locked)
>> {
>> struct fixed_file_data *data = ctx->file_data;
>> struct fixed_file_ref_node *backup_node, *ref_node = NULL;
>> @@ -7872,13 +7872,13 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
>>
>> ret = io_sqe_files_scm(ctx);
>> if (ret) {
>> - io_sqe_files_unregister(ctx);
>> + io_sqe_files_unregister(ctx, true);
>> return ret;
>> }
>>
>> ref_node = alloc_fixed_file_ref_node(ctx);
>> if (!ref_node) {
>> - io_sqe_files_unregister(ctx);
>> + io_sqe_files_unregister(ctx, true);
>> return -ENOMEM;
>> }
>>
>> @@ -8682,7 +8682,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
>> css_put(ctx->sqo_blkcg_css);
>> #endif
>>
>> - io_sqe_files_unregister(ctx);
>> + io_sqe_files_unregister(ctx, false);
>> io_eventfd_unregister(ctx);
>> io_destroy_buffers(ctx);
>> idr_destroy(&ctx->personality_idr);
>> @@ -10065,7 +10065,7 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
>> ret = -EINVAL;
>> if (arg || nr_args)
>> break;
>> - ret = io_sqe_files_unregister(ctx);
>> + ret = io_sqe_files_unregister(ctx, true);
>> break;
>> case IORING_REGISTER_FILES_UPDATE:
>> ret = io_sqe_files_update(ctx, arg, nr_args);
>>
>