slub: use jitter-free reference while printing age
Subsystems (2)
PATCH v2 1/1 slub: use jitter-free reference while printing age
When SLUB_DEBUG catches the some issues, it prints all the required debug info. However, in few cases where allocation and free of the object has have happened in a very short time, 'age' might mislead. See the example below,
[ 6044.137581] ============================================================================= [ 6044.145863] BUG kmalloc-256 (Tainted: G W O ): Poison overwritten [ 6044.152889] ----------------------------------------------------------------------------- ... [ 6044.170804] INFO: Allocated in binder_transaction+0x4b0/0x2448 age=731 cpu=3 pid=5314 ... [ 6044.216696] INFO: Freed in binder_free_transaction+0x2c/0x58 age=735 cpu=6 pid=2079 ... [ 6044.494293] Object fffffff14956a870: 6b 6b 6b 6b 6b 6b 6b 6b 67 6b 6b 6b 6b 6b 6b a5 kkkkkkkkgkkkk
In this case, object got freed later but 'age' shows otherwise. This could be because, while printing this info, we print allocation traces first and free traces thereafter. In between, if we get schedule out or jiffies increment, (jiffies - t->when) could become meaningless.
Use the jitter free reference to calculate age.
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Changes from V1->V2
* Use 'age' with common jiffies for both prints
* Trimmed commit text for clear visibility
mm/slub.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
mm/slub.c +5 -4
@@ -598,13 +598,13 @@ static void init_tracking(struct kmem_cache *s, void *object)set_track (s, object,TRACK_ALLOC ,0UL ); } -static void print_track (const char *s,struct track *t) +static void print_track (const char *s,struct track *t,unsigned long pr_time) {if (!t->addr)return ;pr_err ("INFO: %s in %pS age=%lu cpu=%u pid=%d\n" , - s, (void *)t->addr, jiffies - t->when, t->cpu, t->pid); + s, (void *)t->addr, pr_time - t->when, t->cpu, t->pid);#ifdef CONFIG_STACKTRACE {int i;
@@ -619,11 +619,12 @@ static void print_track(const char *s, struct track *t)static void print_tracking (struct kmem_cache *s,void *object) { +unsigned long pr_time = jiffies;if (!(s->flags &SLAB_STORE_USER ))return ; -print_track ("Allocated" ,get_track (s, object,TRACK_ALLOC )); -print_track ("Freed" ,get_track (s, object,TRACK_FREE )); +print_track ("Allocated" ,get_track (s, object,TRACK_ALLOC ), pr_time); +print_track ("Freed" ,get_track (s, object,TRACK_FREE ), pr_time); }static void print_page_info (struct page *page)
Signature · 3 lines
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc., is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
Quoted 6 lines · Chintan Pandya
In this case, object got freed later but 'age' shows otherwise. This could be because, while printing this info, we print allocation traces first and free traces thereafter. In between, if we get schedule out or jiffies increment, (jiffies -
t->when) could become meaningless.
Could you show the new output style too?
Quoted 10 lines · Christopher Lameter
Quoted 6 lines · Chintan Pandya
In this case, object got freed later but 'age' shows otherwise. This could be because, while printing this info, we print allocation traces first and free traces thereafter. In between, if we get schedule out or jiffies increment, (jiffies -
t->when) could become meaningless.Could you show the new output style too?
New output will exactly be same. 'age' is still
staying with single jiffies ref in both prints.
Quoted 2 lines
Thanks
Chintan
Signature · 3 lines
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project