Re: [PATCH 0/5] SLUB debugfs improvements based on stackdepot

[Vlastimil Babka]

On 2/26/22 13:18, Hyeonggon Yoo wrote:
> On Fri, Feb 25, 2022 at 07:03:13PM +0100, Vlastimil Babka wrote:
>> Hi,
>>
>> this series combines and revives patches from Oliver's last year
>> bachelor thesis (where I was the advisor) that make SLUB's debugfs
>> files alloc_traces and free_traces more useful.
>> The resubmission was blocked on stackdepot changes that are now merged,
>> as explained in patch 2.
>>
>> Patch 1 is a new preparatory cleanup.
>>
>> Patch 2 originally submitted here [1], was merged to mainline but
>> reverted for stackdepot related issues as explained in the patch.
>>
>> Patches 3-5 originally submitted as RFC here [2]. In this submission I
>> have omitted the new file 'all_objects' (patch 3/3 in [2]) as it might
>> be considered too intrusive so I will postpone it for later. The docs
>> patch is adjusted accordingly.
>>
> 
> This problem is not caused by this patch series.
> But I think it's worth mentioning...
> 
> It's really weird that some stack traces are not recorded
> when CONFIG_KASAN=y.
> 
> I made sure that:
> 	- Stack Depot did not reach its limit
> 	- the free path happen on CONFIG_KASAN=y too.
> 
> I have no clue why this happen.
> 
> # cat dentry/free_traces (CONFIG_KASAN=y)
>    6585 <not-available> age=4294912647 pid=0 cpus=0

I think it's some kind of KASAN quarantining of freed objects, so they
haven't been properly freed through the SLUB layer yet.

> # cat dentry/free_traces (CONFIG_KASAN=n)
>    1246 <not-available> age=4294906877 pid=0 cpus=0
>     379 __d_free+0x20/0x2c age=33/14225/14353 pid=0-122 cpus=0-3
>         kmem_cache_free+0x1f4/0x21c
>         __d_free+0x20/0x2c
>         rcu_core+0x334/0x580
>         rcu_core_si+0x14/0x20
>         __do_softirq+0x12c/0x2a8
> 
>       2 dentry_free+0x58/0xb0 age=14101/14101/14101 pid=158 cpus=0
>         kmem_cache_free+0x1f4/0x21c
>         dentry_free+0x58/0xb0
>         __dentry_kill+0x18c/0x1d0
>         dput+0x1c4/0x2fc
>         __fput+0xb0/0x230
>         ____fput+0x14/0x20
>         task_work_run+0x84/0x17c
>         do_notify_resume+0x208/0x1330
>         el0_svc+0x6c/0x80
>         el0t_64_sync_handler+0xa8/0x130
>         el0t_64_sync+0x1a0/0x1a4
> 
>       1 dentry_free+0x58/0xb0 age=7678 pid=190 cpus=1
>         kmem_cache_free+0x1f4/0x21c
>         dentry_free+0x58/0xb0
>         __dentry_kill+0x18c/0x1d0
>         dput+0x1c4/0x2fc
>         __fput+0xb0/0x230
>         ____fput+0x14/0x20
>         task_work_run+0x84/0x17c
>         do_exit+0x2dc/0x8e0
>         do_group_exit+0x38/0xa4
>         __wake_up_parent+0x0/0x34
>         invoke_syscall+0x48/0x114
>         el0_svc_common.constprop.0+0x44/0xfc
>         do_el0_svc+0x2c/0x94
>         el0_svc+0x28/0x80
>         el0t_64_sync_handler+0xa8/0x130
>         el0t_64_sync+0x1a0/0x1a4