Messages in this thread | | | Date | Wed, 17 Nov 2021 14:13:35 -0800 | From | Minchan Kim <> | Subject | Re: [RFC PATCH] kernfs: release kernfs_mutex before the inode allocation |
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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?
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