On Sat, May 03, 2014 at 11:07:57AM -0700, Linus Torvalds wrote:
> Sure, umount itself should be serialized by the sb lock, so there
> should be only one umount dentry collector. But why wouldn't there be
> shrinkers active due to memory pressure?
>
> generic_unmount_super() is called by ->kill_sb(), which is done
> *before* the superblock shrinker is unregistered So any memory
> pressure during that will cause dentries to be shrunk other ways.
>
> What am I missing?
This:
if (!grab_super_passive(sb))
return SHRINK_STOP;
before calling prune_dcache_sb(). grab_super_passive() returns with
->s_umount held shared on success (with down_read_trylock()) and ->kill_sb()
is called only with ->s_umount held exclusive.
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