On 2/5/25 18:10, David Rientjes wrote:
> On Wed, 5 Feb 2025, Hyesoo Yu wrote:
>
>> If a slab object is corrupted or an error occurs in its internal
>> value, continuing after restoration may cause other side effects.
>> At this point, it is difficult to debug because the problem occurred
>> in the past. It is better to use WARN() instead of pr_err to catch
>> errors at the point of issue because WARN() could trigger panic for
>> system debugging when panic_on_warn is enabled. WARN() should be
>> called prior to fixing the value because when a panic is triggered by WARN(),
>> it allows us to check corrupted data.
>>
>
> I think this makes sense, but it doesn't document why the other changes
> are being made, like moving the setting of *freelist to NULL. This is
> presumably something that you want in the crash dump when
> kernel.panic_on_warn is enabled. Probably best to call that out, but to
> also indicate what you're relying on in the crash dump to make forward
> progress on in diagnosing the issue.
Well the last sentence of the changelog above says exactly that, no?
>> Changes in v2:
>> - Replace direct calling with BUG_ON with the use of WARN in slab_fix.
>>
>> Signed-off-by: Hyesoo Yu <hyesoo.yu@xxxxxxxxxxx>
>> ---
>> mm/slub.c | 10 +++++-----
>> 1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 1f50129dcfb3..ea956cb4b8be 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -1043,7 +1043,7 @@ static void slab_fix(struct kmem_cache *s, char *fmt, ...)
>> va_start(args, fmt);
>> vaf.fmt = fmt;
>> vaf.va = &args;
>> - pr_err("FIX %s: %pV\n", s->name, &vaf);
>> + WARN(1, "FIX %s: %pV\n", s->name, &vaf);
>> va_end(args);
>> }
>>
>> @@ -1106,8 +1106,8 @@ static bool freelist_corrupted(struct kmem_cache *s, struct slab *slab,
>> if ((s->flags & SLAB_CONSISTENCY_CHECKS) &&
>> !check_valid_pointer(s, slab, nextfree) && freelist) {
>> object_err(s, slab, *freelist, "Freechain corrupt");
>> - *freelist = NULL;
>> slab_fix(s, "Isolate corrupted freechain");
>> + *freelist = NULL;
>> return true;
>> }
>>
>> @@ -1445,9 +1445,9 @@ static int on_freelist(struct kmem_cache *s, struct slab *slab, void *search)
>> set_freepointer(s, object, NULL);
>> } else {
>> slab_err(s, slab, "Freepointer corrupt");
>> + slab_fix(s, "Freelist cleared");
>> slab->freelist = NULL;
>> slab->inuse = slab->objects;
>> - slab_fix(s, "Freelist cleared");
>> return 0;
>> }
>> break;
>> @@ -1464,14 +1464,14 @@ static int on_freelist(struct kmem_cache *s, struct slab *slab, void *search)
>> if (slab->objects != max_objects) {
>> slab_err(s, slab, "Wrong number of objects. Found %d but should be %d",
>> slab->objects, max_objects);
>> - slab->objects = max_objects;
>> slab_fix(s, "Number of objects adjusted");
>> + slab->objects = max_objects;
>> }
>> if (slab->inuse != slab->objects - nr) {
>> slab_err(s, slab, "Wrong object count. Counter is %d but counted were %d",
>> slab->inuse, slab->objects - nr);
>> - slab->inuse = slab->objects - nr;
>> slab_fix(s, "Object count adjusted");
>> + slab->inuse = slab->objects - nr;
>> }
>> return search == NULL;
>> }
>> --
>> 2.48.0
>>
>>
