* [PATCH] mm: slub: remove dead and buggy code from sysfs_slab_add()
@ 2022-09-30 8:47 Rasmus Villemoes
2022-10-03 7:02 ` Hyeonggon Yoo
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Rasmus Villemoes @ 2022-09-30 8:47 UTC (permalink / raw)
To: Christoph Lameter, Pekka Enberg, David Rientjes, Joonsoo Kim,
Andrew Morton, Vlastimil Babka, Roman Gushchin, Hyeonggon Yoo
Cc: Rasmus Villemoes, linux-mm, linux-kernel
The function sysfs_slab_add() has two callers:
One is slab_sysfs_init(), which first initializes slab_kset, and only
when that succeeds sets slab_state to FULL, and then proceeds to call
sysfs_slab_add() for all previously created slabs.
The other is __kmem_cache_create(), but only after a
if (slab_state <= UP)
return 0;
check.
So in other words, sysfs_slab_add() is never called without
slab_kset (aka the return value of cache_kset()) being non-NULL.
And this is just as well, because if we ever did take this path and
called kobject_init(&s->kobj), and then later when called again from
slab_sysfs_init() would end up calling kobject_init_and_add(), we
would hit
if (kobj->state_initialized) {
/* do not error out as sometimes we can recover */
pr_err("kobject (%p): tried to init an initialized object, something is seriously wrong.\n",
dump_stack();
}
in kobject.c.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
mm/slub.c | 5 -----
1 file changed, 5 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 4b98dff9be8e..04a7f75a7b1f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5937,11 +5937,6 @@ static int sysfs_slab_add(struct kmem_cache *s)
struct kset *kset = cache_kset(s);
int unmergeable = slab_unmergeable(s);
- if (!kset) {
- kobject_init(&s->kobj, &slab_ktype);
- return 0;
- }
-
if (!unmergeable && disable_higher_order_debug &&
(slub_debug & DEBUG_METADATA_FLAGS))
unmergeable = 1;
--
2.37.2
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] mm: slub: remove dead and buggy code from sysfs_slab_add()
2022-09-30 8:47 [PATCH] mm: slub: remove dead and buggy code from sysfs_slab_add() Rasmus Villemoes
@ 2022-10-03 7:02 ` Hyeonggon Yoo
2022-10-03 9:38 ` Rasmus Villemoes
2022-10-10 3:54 ` David Rientjes
2022-10-14 8:15 ` Vlastimil Babka
2 siblings, 1 reply; 6+ messages in thread
From: Hyeonggon Yoo @ 2022-10-03 7:02 UTC (permalink / raw)
To: Rasmus Villemoes
Cc: Christoph Lameter, Pekka Enberg, David Rientjes, Joonsoo Kim,
Andrew Morton, Vlastimil Babka, Roman Gushchin, linux-mm,
linux-kernel
On Fri, Sep 30, 2022 at 10:47:42AM +0200, Rasmus Villemoes wrote:
> The function sysfs_slab_add() has two callers:
>
> One is slab_sysfs_init(), which first initializes slab_kset, and only
> when that succeeds sets slab_state to FULL, and then proceeds to call
> sysfs_slab_add() for all previously created slabs.
>
> The other is __kmem_cache_create(), but only after a
>
> if (slab_state <= UP)
> return 0;
>
> check.
>
> So in other words, sysfs_slab_add() is never called without
> slab_kset (aka the return value of cache_kset()) being non-NULL.
>
> And this is just as well, because if we ever did take this path and
> called kobject_init(&s->kobj), and then later when called again from
> slab_sysfs_init() would end up calling kobject_init_and_add(), we
> would hit
>
> if (kobj->state_initialized) {
> /* do not error out as sometimes we can recover */
> pr_err("kobject (%p): tried to init an initialized object, something is seriously wrong.\n",
> dump_stack();
> }
>
> in kobject.c.
>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> ---
> mm/slub.c | 5 -----
> 1 file changed, 5 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 4b98dff9be8e..04a7f75a7b1f 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5937,11 +5937,6 @@ static int sysfs_slab_add(struct kmem_cache *s)
> struct kset *kset = cache_kset(s);
> int unmergeable = slab_unmergeable(s);
>
> - if (!kset) {
> - kobject_init(&s->kobj, &slab_ktype);
> - return 0;
> - }
> -
> if (!unmergeable && disable_higher_order_debug &&
> (slub_debug & DEBUG_METADATA_FLAGS))
> unmergeable = 1;
> --
> 2.37.2
I assumed that it's hit when SLUB failed to initialize slab_kset in
slab_sysfs_init(). (Yeah, it is too unlikely, though....)
And obviously it's a bug if sysfs_slab_add() is called early than
slab_sysfs_init().
--
Thanks,
Hyeonggon
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] mm: slub: remove dead and buggy code from sysfs_slab_add()
2022-10-03 7:02 ` Hyeonggon Yoo
@ 2022-10-03 9:38 ` Rasmus Villemoes
2022-10-06 6:20 ` Hyeonggon Yoo
0 siblings, 1 reply; 6+ messages in thread
From: Rasmus Villemoes @ 2022-10-03 9:38 UTC (permalink / raw)
To: Hyeonggon Yoo
Cc: Christoph Lameter, Pekka Enberg, David Rientjes, Joonsoo Kim,
Andrew Morton, Vlastimil Babka, Roman Gushchin, linux-mm,
linux-kernel
On 03/10/2022 09.02, Hyeonggon Yoo wrote:
> On Fri, Sep 30, 2022 at 10:47:42AM +0200, Rasmus Villemoes wrote:
>> The function sysfs_slab_add() has two callers:
>>
>> One is slab_sysfs_init(), which first initializes slab_kset, and only
>> when that succeeds sets slab_state to FULL, and then proceeds to call
>> sysfs_slab_add() for all previously created slabs.
>>
>> The other is __kmem_cache_create(), but only after a
>>
>> if (slab_state <= UP)
>> return 0;
>>
>> check.
>>
>> So in other words, sysfs_slab_add() is never called without
>> slab_kset (aka the return value of cache_kset()) being non-NULL.
>>
>> And this is just as well, because if we ever did take this path and
>> called kobject_init(&s->kobj), and then later when called again from
>> slab_sysfs_init() would end up calling kobject_init_and_add(), we
>> would hit
>>
>> if (kobj->state_initialized) {
>> /* do not error out as sometimes we can recover */
>> pr_err("kobject (%p): tried to init an initialized object, something is seriously wrong.\n",
>> dump_stack();
>> }
>>
>> in kobject.c.
>>
>> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
>> ---
>> mm/slub.c | 5 -----
>> 1 file changed, 5 deletions(-)
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 4b98dff9be8e..04a7f75a7b1f 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -5937,11 +5937,6 @@ static int sysfs_slab_add(struct kmem_cache *s)
>> struct kset *kset = cache_kset(s);
>> int unmergeable = slab_unmergeable(s);
>>
>> - if (!kset) {
>> - kobject_init(&s->kobj, &slab_ktype);
>> - return 0;
>> - }
>> -
>> if (!unmergeable && disable_higher_order_debug &&
>> (slub_debug & DEBUG_METADATA_FLAGS))
>> unmergeable = 1;
>> --
>> 2.37.2
>
> I assumed that it's hit when SLUB failed to initialize slab_kset in
> slab_sysfs_init(). (Yeah, it is too unlikely, though....)
No, it is not, because if the creation of slab_kset fails,
slab_sysfs_init() returns early, and hence slab_state never transitions
to FULL. I don't see anywhere else where slab_state could become FULL
(of course in slab.c and slob.c, but those are not built when slub.c
is), so I do believe my analysis in the commit log is correct.
> And obviously it's a bug if sysfs_slab_add() is called early than
> slab_sysfs_init().
Yes, and that's already what the existing slab_state check guards.
Rasmus
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] mm: slub: remove dead and buggy code from sysfs_slab_add()
2022-10-03 9:38 ` Rasmus Villemoes
@ 2022-10-06 6:20 ` Hyeonggon Yoo
0 siblings, 0 replies; 6+ messages in thread
From: Hyeonggon Yoo @ 2022-10-06 6:20 UTC (permalink / raw)
To: Rasmus Villemoes
Cc: Christoph Lameter, Pekka Enberg, David Rientjes, Joonsoo Kim,
Andrew Morton, Vlastimil Babka, Roman Gushchin, linux-mm,
linux-kernel
On Mon, Oct 03, 2022 at 11:38:30AM +0200, Rasmus Villemoes wrote:
> On 03/10/2022 09.02, Hyeonggon Yoo wrote:
> > On Fri, Sep 30, 2022 at 10:47:42AM +0200, Rasmus Villemoes wrote:
> >> The function sysfs_slab_add() has two callers:
> >>
> >> One is slab_sysfs_init(), which first initializes slab_kset, and only
> >> when that succeeds sets slab_state to FULL, and then proceeds to call
> >> sysfs_slab_add() for all previously created slabs.
> >>
> >> The other is __kmem_cache_create(), but only after a
> >>
> >> if (slab_state <= UP)
> >> return 0;
> >>
> >> check.
> >>
> >> So in other words, sysfs_slab_add() is never called without
> >> slab_kset (aka the return value of cache_kset()) being non-NULL.
> >>
> >> And this is just as well, because if we ever did take this path and
> >> called kobject_init(&s->kobj), and then later when called again from
> >> slab_sysfs_init() would end up calling kobject_init_and_add(), we
> >> would hit
> >>
> >> if (kobj->state_initialized) {
> >> /* do not error out as sometimes we can recover */
> >> pr_err("kobject (%p): tried to init an initialized object, something is seriously wrong.\n",
> >> dump_stack();
> >> }
> >>
> >> in kobject.c.
> >>
> >> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> >> ---
> >> mm/slub.c | 5 -----
> >> 1 file changed, 5 deletions(-)
> >>
> >> diff --git a/mm/slub.c b/mm/slub.c
> >> index 4b98dff9be8e..04a7f75a7b1f 100644
> >> --- a/mm/slub.c
> >> +++ b/mm/slub.c
> >> @@ -5937,11 +5937,6 @@ static int sysfs_slab_add(struct kmem_cache *s)
> >> struct kset *kset = cache_kset(s);
> >> int unmergeable = slab_unmergeable(s);
> >>
> >> - if (!kset) {
> >> - kobject_init(&s->kobj, &slab_ktype);
> >> - return 0;
> >> - }
> >> -
> >> if (!unmergeable && disable_higher_order_debug &&
> >> (slub_debug & DEBUG_METADATA_FLAGS))
> >> unmergeable = 1;
> >> --
> >> 2.37.2
> >
> > I assumed that it's hit when SLUB failed to initialize slab_kset in
> > slab_sysfs_init(). (Yeah, it is too unlikely, though....)
>
> No, it is not, because if the creation of slab_kset fails,
> slab_sysfs_init() returns early, and hence slab_state never transitions
> to FULL.
Yeah, you are right ;-) I misread that.
> I don't see anywhere else where slab_state could become FULL
> (of course in slab.c and slob.c, but those are not built when slub.c
> is), so I do believe my analysis in the commit log is correct.
Right.
> > And obviously it's a bug if sysfs_slab_add() is called early than
> > slab_sysfs_init().
>
> Yes, and that's already what the existing slab_state check guards.
>
> Rasmus
Looks good to me,
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Thanks!
--
Thanks,
Hyeonggon
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] mm: slub: remove dead and buggy code from sysfs_slab_add()
2022-09-30 8:47 [PATCH] mm: slub: remove dead and buggy code from sysfs_slab_add() Rasmus Villemoes
2022-10-03 7:02 ` Hyeonggon Yoo
@ 2022-10-10 3:54 ` David Rientjes
2022-10-14 8:15 ` Vlastimil Babka
2 siblings, 0 replies; 6+ messages in thread
From: David Rientjes @ 2022-10-10 3:54 UTC (permalink / raw)
To: Rasmus Villemoes
Cc: Christoph Lameter, Pekka Enberg, Joonsoo Kim, Andrew Morton,
Vlastimil Babka, Roman Gushchin, Hyeonggon Yoo, linux-mm,
linux-kernel
On Fri, 30 Sep 2022, Rasmus Villemoes wrote:
> The function sysfs_slab_add() has two callers:
>
> One is slab_sysfs_init(), which first initializes slab_kset, and only
> when that succeeds sets slab_state to FULL, and then proceeds to call
> sysfs_slab_add() for all previously created slabs.
>
> The other is __kmem_cache_create(), but only after a
>
> if (slab_state <= UP)
> return 0;
>
> check.
>
> So in other words, sysfs_slab_add() is never called without
> slab_kset (aka the return value of cache_kset()) being non-NULL.
>
> And this is just as well, because if we ever did take this path and
> called kobject_init(&s->kobj), and then later when called again from
> slab_sysfs_init() would end up calling kobject_init_and_add(), we
> would hit
>
> if (kobj->state_initialized) {
> /* do not error out as sometimes we can recover */
> pr_err("kobject (%p): tried to init an initialized object, something is seriously wrong.\n",
> dump_stack();
> }
>
> in kobject.c.
>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: David Rientjes <rientjes@google.com>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] mm: slub: remove dead and buggy code from sysfs_slab_add()
2022-09-30 8:47 [PATCH] mm: slub: remove dead and buggy code from sysfs_slab_add() Rasmus Villemoes
2022-10-03 7:02 ` Hyeonggon Yoo
2022-10-10 3:54 ` David Rientjes
@ 2022-10-14 8:15 ` Vlastimil Babka
2 siblings, 0 replies; 6+ messages in thread
From: Vlastimil Babka @ 2022-10-14 8:15 UTC (permalink / raw)
To: Rasmus Villemoes, Christoph Lameter, Pekka Enberg,
David Rientjes, Joonsoo Kim, Andrew Morton, Roman Gushchin,
Hyeonggon Yoo
Cc: linux-mm, linux-kernel
On 9/30/22 10:47, Rasmus Villemoes wrote:
> The function sysfs_slab_add() has two callers:
>
> One is slab_sysfs_init(), which first initializes slab_kset, and only
> when that succeeds sets slab_state to FULL, and then proceeds to call
> sysfs_slab_add() for all previously created slabs.
>
> The other is __kmem_cache_create(), but only after a
>
> if (slab_state <= UP)
> return 0;
>
> check.
>
> So in other words, sysfs_slab_add() is never called without
> slab_kset (aka the return value of cache_kset()) being non-NULL.
>
> And this is just as well, because if we ever did take this path and
> called kobject_init(&s->kobj), and then later when called again from
> slab_sysfs_init() would end up calling kobject_init_and_add(), we
> would hit
>
> if (kobj->state_initialized) {
> /* do not error out as sometimes we can recover */
> pr_err("kobject (%p): tried to init an initialized object, something is seriously wrong.\n",
> dump_stack();
> }
>
> in kobject.c.
>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Thanks, added to slab.git for-6.2/slub-sysfs
> ---
> mm/slub.c | 5 -----
> 1 file changed, 5 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 4b98dff9be8e..04a7f75a7b1f 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5937,11 +5937,6 @@ static int sysfs_slab_add(struct kmem_cache *s)
> struct kset *kset = cache_kset(s);
> int unmergeable = slab_unmergeable(s);
>
> - if (!kset) {
> - kobject_init(&s->kobj, &slab_ktype);
> - return 0;
> - }
> -
> if (!unmergeable && disable_higher_order_debug &&
> (slub_debug & DEBUG_METADATA_FLAGS))
> unmergeable = 1;
^ permalink raw reply [flat|nested] 6+ messages in thread
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2022-09-30 8:47 [PATCH] mm: slub: remove dead and buggy code from sysfs_slab_add() Rasmus Villemoes
2022-10-03 7:02 ` Hyeonggon Yoo
2022-10-03 9:38 ` Rasmus Villemoes
2022-10-06 6:20 ` Hyeonggon Yoo
2022-10-10 3:54 ` David Rientjes
2022-10-14 8:15 ` Vlastimil Babka
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