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

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Date:   Sat, 26 Feb 2022 12:18:24 +0000
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     David Rientjes <rientjes@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Pekka Enberg <penberg@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        patches@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Oliver Glitta <glittao@...il.com>,
        Faiyaz Mohammed <faiyazm@...eaurora.org>,
        Jonathan Corbet <corbet@....net>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH 0/5] SLUB debugfs improvements based on stackdepot

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

# 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
-- 
Thank you, You are awesome!
Hyeonggon :-)