Re: [PATCH 1/8] ext4: free the sbi after a grace period

[sashiko-bot@kernel.org]

> ext4_get_link() follows a symlink that keeps its target in a data block
> in rcu pathwalk mode with ext4_getblk(EXT4_GET_BLOCKS_CACHED_NOWAIT).
> That reads s_mount_state in the ASSERT() of ext4_getblk() and again in
> ext4_es_lookup_extent(), and the lookup bumps the extent status hit or
> miss counter, all through sb->s_fs_info.
> 
> ext4_put_super() destroys those counters, clears sb->s_fs_info and frees
> the sbi without waiting for a grace period. A pathwalk that is still in
> ext4_get_link() when the last reference to the mount goes away then
> dereferences a NULL s_fs_info, the freed sbi or the destroyed percpu
> counters.
> 
> With a pathwalk held up in ext4_get_link() while the last reference
> goes away:
> 
> [ ... ]
> in ext4_put_super(), the counters go with the sbi.
> 
> Fixes: 6493792d3299 ("ext4: convert symlink external data block mapping to bdev")
> Cc: stable@vger.kernel.org
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20261009-work-fixes-rcu-v1-0-7446d2d335e6@kernel.org?part=1