Re: [PATCH 1/2] dcache: don't leave negative dentries in casefolded directories

[sashiko-bot@kernel.org]

> ext4, f2fs and tmpfs keep negative dentries out of casefolded
> directories. A negative dentry remembers one spelling of the name and
> the next create() through it would write that spelling to disk.
> 
> So their ->lookup() doesn't cache a miss and their ->unlink() and
> ->rmdir() call d_invalidate() on the dentry so that d_delete() doesn't
> turn it into a negative dentry.
> 
> But d_invalidate() is the wrong primitive for that. It's for a name that
> went stale. It walks the subtree, prunes it and detaches every mount it
> finds, under namespace_sem, and here that runs from inside the
> filesystem's own directory operation. ext4_rmdir() does it with the
> journal handle still open and ext4_unlink() does it even when the
> unlink failed. All anyone wanted is the unhash.
> 
> So d_delete() now unhashes the dentry when the parent is casefolded,
> next to the dentry-negative sysctl that does the same for every
> directory. ext4, f2fs and tmpfs drop their d_invalidate() calls.
> 
> Nothing changes for a casefolded directory. A miss still isn't cached
> and a removed name still doesn't leave a negative dentry behind. The
> target of a rename over an existing name, which tmpfs also passes
> through shmem_unlink(), doesn't turn negative either. vfs_rename()
> detaches its mounts and d_move() unhashes it. A failed unlink or rmdir
> now leaves the dentry hashed and its mounts in place, as in any other
> directory.
> 
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261023-work-dcache-casefold-v1-0-1b0bd5c73a69@kernel.org?part=1