在 2021/8/20 下午8:26, Pavel Begunkov 写道:
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.
Thanks, got it.
