lkml.org 
[lkml]   [2022]   [Feb]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 1/2] io_uring: avoid ring quiesce while registering/unregistering eventfd
From
Date
On 2/3/22 9:49 AM, Usama Arif wrote:
>> One thing that both mine and your version suffers from is if someone
>> does an eventfd unregister, and then immediately does an eventfd
>> register. If the rcu grace period hasn't passed, we'll get -EBUSY on
>> trying to do that, when I think the right behavior there would be to
>> wait for the grace period to pass.
>>
>> I do think we need to handle that gracefully, spurious -EBUSY is
>> impossible for an application to deal with.
>
> I don't think my version would suffer from this as its protected by
> locks? The mutex_unlock on ev_fd_lock in unregister happens only after
> the call_rcu. And the mutex is locked in io_eventfd_register at the
> start, so wouldnt get the -EBUSY if there is a register immediately
> after unregister?

The call_rcu() just registers it for getting the callback when the grace
period has passed, it doesn't mean it's done by the time it returns.
Hence there's definitely a window where you can enter
io_uring_register() with the callback still being pending, and you'd get
-EBUSY from that.

--
Jens Axboe

\
 
 \ /
  Last update: 2022-02-03 17:59    [W:0.063 / U:0.400 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site