Re: [PATCH v3] mm/slub: Fix incorrect interpretation of s->offset

[Waiman Long]

On 4/29/20 9:53 AM, Waiman Long wrote:
> In a couple of places in the slub memory allocator, the code uses
> "s->offset" as a check to see if the free pointer is put right after the
> object. That check is no longer true with commit 3202fa62fb43 ("slub:
> relocate freelist pointer to middle of object").
>
> As a result, echoing "1" into the validate sysfs file, e.g. of dentry,
> may cause a bunch of "Freepointer corrupt" error reports like the
> following to appear with the system in panic afterwards.
>
> [   38.579769] =============================================================================
> [   38.580845] BUG dentry(666:pmcd.service) (Tainted: G    B): Freepointer corrupt
> [   38.581948] -----------------------------------------------------------------------------
>
> To fix it, use the check "s->offset == s->inuse" in the new helper

Sorry, forgot to change the commit log to ">=". Anyway, this is a 
serious bug that needs to be fixed before v5.7 is released.

Cheers,
Longman