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Message-ID: <20250210035336.GA1868980@tiffany>
Date: Mon, 10 Feb 2025 12:53:40 +0900
From: Hyesoo Yu <hyesoo.yu@...sung.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: janghyuck.kim@...sung.com, Christoph Lameter <cl@...ux.com>, Pekka
Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo
Kim <iamjoonsoo.kim@....com>, Andrew Morton <akpm@...ux-foundation.org>,
Roman Gushchin <roman.gushchin@...ux.dev>, Hyeonggon Yoo
<42.hyeyoo@...il.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: slub: call WARN() instead of pr_err on slab_fix.
On Fri, Feb 07, 2025 at 10:08:20AM +0100, Vlastimil Babka wrote:
> On 2/7/25 04:28, Hyesoo Yu wrote:
> > On Thu, Feb 06, 2025 at 12:35:22PM +0100, Vlastimil Babka wrote:
> >> On 2/5/25 01:46, 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.
> >> >
> >> > Changes in v2:
> >> > - Replace direct calling with BUG_ON with the use of WARN in slab_fix.
> >> >
> >> > Signed-off-by: Hyesoo Yu <hyesoo.yu@...sung.com>
> >>
> >> Hi and thanks for the patch,
> >>
> >> I wonder if it would be better not to change slab_fix() but rather
> >> slab_err() and object_err(). It wouldn't then require to rearrange the fixup
> >> code. Also I think some error reporting paths don't go through slab_fix()
> >> and we still would like them to become a WARN too.
> >>
> >> Basically it would mean the last line in slab_err() would be a WARN and we'd
> >> drop the dump_stack() as that's redundant. Same in object_err() (no
> >> dump_stack() there). It would be a bit noisier as a result, but hopefully
> >> acceptable. The slab specific debugging info would still be printed before
> >> the WARN hits (and potentially results in a panic) so anyone investigating
> >> the crash dump would have that information.
> >>
> >> Hm but I see some places print stuff after slab_err(). slab_pad_check() and
> >> list_slab_objects(). We could create slab_err_start() and slab_err_end() for
> >> those, and slab_err() would just call both at once.
> >>
> >
> > Thank you so much for your review.
> >
> > That's a great suggestion. Following your suggestion, it seems possible to use
> > WARN on all error reporting paths. For some places print stuff after slab_err,
> > print them as follows,
> >
> > +static void __slab_err(struct slab *slab)
> > +{
> > + print_slab_info(slab);
> > + add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
> > +
> > + WARN_ON(1);
> > +}
> > +
> > static __printf(3, 4) void slab_err(struct kmem_cache *s, struct slab *slab,
> > const char *fmt, ...)
> > {
> > vsnprintf(buf, sizeof(buf), fmt, args);
> > va_end(args);
> > slab_bug(s, "%s", buf);
> > - print_slab_info(slab);
> > - dump_stack();
> > - add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
> > + __slab_err(slab);
> > }
> >
> > @@ -1316,11 +1322,13 @@ slab_pad_check(struct kmem_cache *s, struct slab *slab)
> > while (end > fault && end[-1] == POISON_INUSE)
> > end--;
> >
> > - slab_err(s, slab, "Padding overwritten. 0x%p-0x%p @offset=%tu",
> > - fault, end - 1, fault - start);
> > + slab_bug(s, "Padding overwritten. 0x%p-0x%p @offset=%tu",
> > + fault, end - 1, fault - start);
> > print_section(KERN_ERR, "Padding ", pad, remainder);
> >
> > restore_bytes(s, "slab padding", POISON_INUSE, fault, end);
> > +
> > + __slab_err(slab);
>
> Yeah but move that above restore_bytes()?
>
Yes, I will.
> BTW I think we could also do this?
>
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1162,7 +1162,7 @@ void skip_orig_size_check(struct kmem_cache *s, const void *object)
> set_orig_size(s, (void *)object, s->object_size);
> }
>
> -static void slab_bug(struct kmem_cache *s, char *fmt, ...)
> +static void slab_bug(struct kmem_cache *s, const char *fmt, ...)
> {
> struct va_format vaf;
> va_list args;
> @@ -1263,15 +1263,11 @@ static __printf(3, 4) void slab_err(struct kmem_cache *s, struct slab *slab,
> const char *fmt, ...)
> {
> va_list args;
> - char buf[100];
>
> if (slab_add_kunit_errors())
> return;
>
> - va_start(args, fmt);
> - vsnprintf(buf, sizeof(buf), fmt, args);
> - va_end(args);
> - slab_bug(s, "%s", buf);
> + slab_bug(s, fmt, args);
>
>
I guess the args is not initialized.
Do you want it to be modified like this ?
Thanks,
Regards.
-static void slab_bug(struct kmem_cache *s, char *fmt, ...)
+static void slab_bug(struct kmem_cache *s, const char *fmt, ...)
{
struct va_format vaf;
va_list args;
@@ -1137,15 +1137,14 @@ static __printf(3, 4) void slab_err(struct kmem_cache *s, struct slab *slab,
const char *fmt, ...)
{
va_list args;
- char buf[100];
if (slab_add_kunit_errors())
return;
va_start(args, fmt);
- vsnprintf(buf, sizeof(buf), fmt, args);
+ slab_bug(s, fmt, args);
va_end(args);
- slab_bug(s, "%s", buf);
> > }
> >
> >> > ---
> >> > 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;
> >> > }
> >>
> >>
> >
> >
>
>
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