lkml.org 
[lkml]   [2021]   [Nov]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH] kernfs: release kernfs_mutex before the inode allocation
Hi Tejun,

On Wed, Nov 17, 2021 at 11:45:46AM -1000, Tejun Heo wrote:
> Hello,
>
> On Tue, Nov 16, 2021 at 11:27:56PM -0800, Minchan Kim wrote:
> > A app launching involves dma_buf exports which creates kobject
> > and add it to the kernfs with down_write - kernfs_add_one.
> >
> > At the same time in other CPU, a random process was accessing
> > sysfs and the kernfs_iop_lookup was already hoding the kernfs_rwsem
> > and ran under direct reclaim patch due to alloc_inode in
> > kerfs_get_inode.
> >
> > Therefore, the app is stuck on the lock and lose frames so enduser
> > sees the jank.
>
> So, one really low hanging fruit here would be using a separate rwsem per
> superblock. Nothing needs synchronization across different users of kernfs
> and the locking is shared just because nobody bothered to separate them out
> while generalizing it from sysfs.

That's really what I wanted but had a question whether we can access
superblock from the kernfs_node all the time since there are some
functions to access the kernfs_rwsem without ionde, sb context.

Is it doable to get the superblock from the kernfs_node all the time?

\
 
 \ /
  Last update: 2021-11-17 23:17    [W:0.091 / U:0.316 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site