lkml.org 
[lkml]   [2020]   [Feb]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: io_uring: io_grab_files() misses taking files->count?
From
Date
On 2/6/20 9:32 AM, Kirill Tkhai wrote:
> Hi, Jens,
>
> in io_grab_files() we take pointer to current->files without taking
> files->count. Later, this files become attached to worker in
> io_worker_handle_work() also without any manipulation with counter.
>
> But files->count is used for different optimizations. Say, in
> expand_fdtable() we avoid synchonize_rcu() in case of there is only
> files user. In case of there are more users, missing of
> synchronize_rcu() is not safe.
>
> Is this correct? Or maybe there is some hidden logic in io_uring,
> which prevents this problem? Say, IORING_OP_OPENAT/CLOSE/ETC can't be
> propagated to worker etc...

We track requests that grab files on the side, since we can't safely
grab a reference to the file table. We could have our own ring fd in the
file table, and thus create a circular reference if we incremented
files->count here.

Looks like we might need a 2nd way to know if we need to use
synchronize_rcu() or not, though I need to look into this particular
case.

--
Jens Axboe

\
 
 \ /
  Last update: 2020-02-06 20:57    [W:0.074 / U:0.336 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site