linux-kernel - Re: [PATCH] mm/vmalloc: Remove WARN_ON_ONCE related to adjust_va_to_fit

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Message-ID: <ZQ1ftk5yDBv+p6A4@MiWiFi-R3L-srv>
Date:   Fri, 22 Sep 2023 17:34:46 +0800
From:   "bhe@...hat.com" <bhe@...hat.com>
To:     Jaeseon Sim <jason.sim@...sung.com>
Cc:     "urezki@...il.com" <urezki@...il.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "lstoakes@...il.com" <lstoakes@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jaewon Kim <jaewon31.kim@...sung.com>
Subject: Re: [PATCH] mm/vmalloc: Remove WARN_ON_ONCE related to
 adjust_va_to_fit_type

Hi Jaeseon,

On 09/22/23 at 03:27pm, Jaeseon Sim wrote:
> There's panic issue as follows when do alloc_vmap_area:
> 
> Kernel panic - not syncing: kernel: panic_on_warn set ...
> 
> page allocation failure: order:0, mode:0x800(GFP_NOWAIT)
> Call Trace:
> warn_alloc+0xf4/0x190
> __alloc_pages_slowpath+0xe0c/0xffc
> __alloc_pages+0x250/0x2d0
> new_slab+0x17c/0x4e0
> ___slab_alloc+0x4e4/0x8a8
> __slab_alloc+0x34/0x6c
> kmem_cache_alloc+0x20c/0x2f0
> adjust_va_to_fit_type
> __alloc_vmap_area
> alloc_vmap_area+0x298/0x7fc
> __get_vm_area_node+0x10c/0x1b4
> __vmalloc_node_range+0x19c/0x7c0
> 
> Commit 1b23ff80b399 ("mm/vmalloc: invoke classify_va_fit_type() in
> adjust_va_to_fit_type()") moved classify_va_fit_type() into
> adjust_va_to_fit_type() and used WARN_ON_ONCE() to handle return
> value of adjust_va_to_fit_type(), just as classify_va_fit_type()
> was handled.

I don't get what you are fixing. In commit 1b23ff80b399, we have
"if (WARN_ON_ONCE(type == NOTHING_FIT))", it's the same as the current
code. You set panic_on_warn, it will panic in old code before commit
1b23ff80b399. Isn't it an expected behaviour?

> 
> There is another path in adjust_va_to_fit_type() which could
> return failure and will be handled in alloc_vmap_area().
> Remove WARN_ON_ONCE() for this case.
> 
> Fixes: 45c62fc2897d ("mm/vmalloc: Remove WARN_ON_ONCE related to adjust_va_to_fit_type")

The commit id for Fixes tag is wrong.

> Signed-off-by: Jaeseon Sim <jason.sim@...sung.com>
> ---
>  mm/vmalloc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index ef8599d394fd..4a82b6525d48 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1522,7 +1522,7 @@ __alloc_vmap_area(struct rb_root *root, struct list_head *head,
>  
>          /* Update the free vmap_area. */
>          ret = adjust_va_to_fit_type(root, head, va, nva_start_addr, size);
> -        if (WARN_ON_ONCE(ret))
> +        if (ret)
>                  return vend;
>  
>  #if DEBUG_AUGMENT_LOWEST_MATCH_CHECK
> @@ -4143,7 +4143,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
>                  ret = adjust_va_to_fit_type(&free_vmap_area_root,
>                                              &free_vmap_area_list,
>                                              va, start, size);
> -                if (WARN_ON_ONCE(unlikely(ret)))
> +                if (unlikely(ret))
>                          /* It is a BUG(), but trigger recovery instead. */
>                          goto recovery;
>  
> -- 
> 2.17.1
>