On 8/20/21 11:16 AM, Hao Xu wrote: > 在 2021/8/20 下午5:49, Pavel Begunkov 写道: >> On 8/20/21 10:21 AM, Hao Xu wrote: >>> 在 2021/8/18 下午7:42, Pavel Begunkov 写道: >>>> io_fallback_req_func() doesn't expect anyone creating inline >>>> completions, and no one currently does that. Teach the function to flush >>>> completions preparing for further changes. >>>> >>>> Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx> >>>> --- >>>> fs/io_uring.c | 5 +++++ >>>> 1 file changed, 5 insertions(+) >>>> >>>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>>> index 3da9f1374612..ba087f395507 100644 >>>> --- a/fs/io_uring.c >>>> +++ b/fs/io_uring.c >>>> @@ -1197,6 +1197,11 @@ static void io_fallback_req_func(struct work_struct *work) >>>> percpu_ref_get(&ctx->refs); >>>> llist_for_each_entry_safe(req, tmp, node, io_task_work.fallback_node) >>>> req->io_task_work.func(req); >>>> + >>>> + mutex_lock(&ctx->uring_lock); >>>> + if (ctx->submit_state.compl_nr) >>>> + io_submit_flush_completions(ctx); >>>> + mutex_unlock(&ctx->uring_lock); >>> why do we protect io_submit_flush_completions() with uring_lock, >>> regarding that it is called in original context. Btw, why not >>> use ctx_flush_and_put() >> >> The fallback thing is called from a workqueue not the submitter task >> context. See delayed_work and so. >> >> Regarding locking, it touches struct io_submit_state, and it's protected by >> ->uring_lock. In particular we're interested in ->reqs and ->free_list. >> FWIW, there is refurbishment going on around submit state, so if proves >> useful the locking may change in coming months. >> >> ctx_flush_and_put() could have been used, but simpler to hand code it >> and avoid the (always messy) conditional ref grabbing and locking. > I didn't get it, what do you mean 'avoid the (always messy) conditional > ref grabbing and locking'? the code here and in ctx_flush_and_put() are > same..though I think in ctx_flush_and_put(), there is a problem that > compl_nr should also be protected. Ok, the long story. First, notice a ctx check at the beginning of ctx_flush_and_put(), that one is conditional. Even though we know it's not NULL, it's more confusing and might be a problem for static and human analysis. Also, locking is never easy, and so IMHO it's preferable to keep lock() and a matching unlock (or get/put) in the same function if possible, much easier to read. Compare ref_get(); do_something(); ref_put(); and ref_get(); do_something(); flush_ctx(); I believe, the first one is of less mental overhead. -- Pavel Begunkov
