linux-kernel - Re: [PATCH 1/1] fixup for mm/debug: print vm

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Message-ID: <xzbyr4v4jhxjovjsbsqikapqddkwyh3sudm3dd3rvxjgcoayda@xqyebxeynnya>
Date: Tue, 7 Jan 2025 13:49:52 -0500
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: akpm@...ux-foundation.org, peterz@...radead.org, willy@...radead.org,
        lorenzo.stoakes@...cle.com, mhocko@...e.com, vbabka@...e.cz,
        hannes@...xchg.org, mjguzik@...il.com, oliver.sang@...el.com,
        mgorman@...hsingularity.net, david@...hat.com, peterx@...hat.com,
        oleg@...hat.com, dave@...olabs.net, paulmck@...nel.org,
        brauner@...nel.org, dhowells@...hat.com, hdanton@...a.com,
        hughd@...gle.com, lokeshgidra@...gle.com, minchan@...gle.com,
        jannh@...gle.com, shakeel.butt@...ux.dev, souravpanda@...gle.com,
        pasha.tatashin@...een.com, klarasmodin@...il.com, corbet@....net,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH 1/1] fixup for mm/debug: print vm_refcnt state when
 dumping the vma

* Suren Baghdasaryan <surenb@...gle.com> [241226 15:03]:
> vma->vm_refcnt does not exist when CONFIG_PER_VMA_LOCK=n, therefore
> when CONFIG_PER_VMA_LOCK=n and CONFIG_DEBUG_VM=y we need to avoid its
> usage in dump_vma().

It might be worth having a function that decodes the information in the
vma lock and outputs a string that spells out what is going on, and
another that just outputs "not supported" or something.

This has the benefit of spelling out the state and only having one place
to update in future dump_vma() changes.

> 
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202412270328.HiJX1mRt-lkp@intel.com/
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> ---
> Fixes https://lore.kernel.org/all/20241226170710.1159679-14-surenb@google.com/
> posted over mm-unstable.
> 
>  mm/debug.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/mm/debug.c b/mm/debug.c
> index 68b3ba3cf603..9c4cbc3733b0 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -178,6 +178,7 @@ EXPORT_SYMBOL(dump_page);
>  
>  void dump_vma(const struct vm_area_struct *vma)
>  {
> +#ifdef CONFIG_PER_VMA_LOCK
>  	pr_emerg("vma %px start %px end %px mm %px\n"
>  		"prot %lx anon_vma %px vm_ops %px\n"
>  		"pgoff %lx file %px private_data %px\n"
> @@ -187,6 +188,17 @@ void dump_vma(const struct vm_area_struct *vma)
>  		vma->anon_vma, vma->vm_ops, vma->vm_pgoff,
>  		vma->vm_file, vma->vm_private_data,
>  		vma->vm_flags, &vma->vm_flags, refcount_read(&vma->vm_refcnt));
> +#else
> +	pr_emerg("vma %px start %px end %px mm %px\n"
> +		"prot %lx anon_vma %px vm_ops %px\n"
> +		"pgoff %lx file %px private_data %px\n"
> +		"flags: %#lx(%pGv)\n",
> +		vma, (void *)vma->vm_start, (void *)vma->vm_end, vma->vm_mm,
> +		(unsigned long)pgprot_val(vma->vm_page_prot),
> +		vma->anon_vma, vma->vm_ops, vma->vm_pgoff,
> +		vma->vm_file, vma->vm_private_data,
> +		vma->vm_flags, &vma->vm_flags);
> +#endif
>  }
>  EXPORT_SYMBOL(dump_vma);
>  
> -- 
> 2.47.1.613.gc27f4b7a9f-goog
>