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

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Date:   Mon, 25 Sep 2023 15:40:32 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Jaeseon Sim <jason.sim@...sung.com>
Cc:     "bhe@...hat.com" <bhe@...hat.com>,
        "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

On Mon, Sep 25, 2023 at 07:51:54PM +0900, Jaeseon Sim wrote:
> > On 09/22/23 at 05:34pm, Baoquan He wrote:
> > > Hi Jaeseon,
> Hello Baoquan,
> > > 
> > > 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
> 
> To Uladzislau,
> Sorry. The path is as below.
> 
> Call trace:
>  alloc_vmap_area+0x298/0x7fc
>  __get_vm_area_node+0x10c/0x1b4
>  __vmalloc_node_range+0x19c/0x7c0
>  dup_task_struct+0x1b8/0x3b0
>  copy_process+0x170/0xc40
> 
> > > > 
> > > > 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
> >                                    ~~ s/In/Before/, typo
> > > "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 a call path which didn't panic in old code, but does on the current.
> 
> static __always_inline int adjust_va_to_fit_type()
> 
> } else if (type == NE_FIT_TYPE) {
> 	lva = kmem_cache_alloc(vmap_area_cachep, GFP_NOWAIT);
> 	if (!lva)
> 		return -1;
> 
>
We do not have above code anymore:

<snip>
commit 82dd23e84be3ead53b6d584d836f51852d1096e6
Author: Uladzislau Rezki (Sony) <urezki@...il.com>
Date:   Thu Jul 11 20:58:57 2019 -0700

    mm/vmalloc.c: preload a CPU with one object for split purpose

<snip>

Which kernel are you testing?

Thanks!

--
Uladzislau Rezki