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 19:51:54 +0900
From:   Jaeseon Sim <jason.sim@...sung.com>
To:     "bhe@...hat.com" <bhe@...hat.com>,
        "urezki@...il.com" <urezki@...il.com>
CC:     "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 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;

If the above path is taken, Retry path should be triggred at alloc_vmap_area(). 
But it is currenly unable to so.

> > 
> > > 
> > > 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
> > > 
> > 
>