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From: Barry Song <21cnbao@gmail.com>
Date: Thu, 9 May 2024 14:26:48 +1200
Message-ID: <CAGsJ_4zZ=nR9ocjrSJNbhU=gKJBC0bqJ306R=GiAAXe2Oda06g@mail.gmail.com>
Subject: Re: [RFC PATCH] mm/vmalloc: fix vmalloc which may return null if
 called with __GFP_NOFAIL
To: hailong.liu@oppo.com, asily.averin@linux.dev, 
	Michal Hocko <mhocko@suse.com>
Cc: akpm@linux-foundation.org, urezki@gmail.com, hch@infradead.org, 
	lstoakes@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, 
	xiang@kernel.org, chao@kernel.org, Oven <liyangouwen1@oppo.com>
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On Thu, May 9, 2024 at 2:20=E2=80=AFPM Barry Song <21cnbao@gmail.com> wrote=
:
>
> On Thu, May 9, 2024 at 12:58=E2=80=AFAM <hailong.liu@oppo.com> wrote:
> >
> > From: "Hailong.Liu" <hailong.liu@oppo.com>
> >
> > Commit a421ef303008 ("mm: allow !GFP_KERNEL allocations for kvmalloc")
> > includes support for __GFP_NOFAIL, but it presents a conflict with
> > commit dd544141b9eb ("vmalloc: back off when the current task is
> > OOM-killed"). A possible scenario is as belows:
> >
> > process-a
> > kvcalloc(n, m, GFP_KERNEL | __GFP_NOFAIL)
> >     __vmalloc_node_range()
> >         __vmalloc_area_node()
> >             vm_area_alloc_pages()
> >             --> oom-killer send SIGKILL to process-a
> >             if (fatal_signal_pending(current)) break;
> > --> return NULL;
> >
> > to fix this, do not check fatal_signal_pending() in vm_area_alloc_pages=
()
> > if __GFP_NOFAIL set.
> >
> > Reported-by: Oven <liyangouwen1@oppo.com>
> > Signed-off-by: Hailong.Liu <hailong.liu@oppo.com>
> > ---
> >  mm/vmalloc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 6641be0ca80b..2f359d08bf8d 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -3560,7 +3560,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
> >
> >         /* High-order pages or fallback path if "bulk" fails. */
> >         while (nr_allocated < nr_pages) {
> > -               if (fatal_signal_pending(current))
> > +               if (!(gfp & __GFP_NOFAIL) && fatal_signal_pending(curre=
nt))
> >                         break;
>
> why not !nofail ?
>
> This seems a correct fix, but it undermines the assumption made in
> commit dd544141b9eb
>  ("vmalloc: back off when the current task is OOM-killed")
>
> "
>     This may trigger some hidden problems, when caller does not handle
>     vmalloc failures, or when rollaback after failed vmalloc calls own
>     vmallocs inside.  However all of these scenarios are incorrect: vmall=
oc
>     does not guarantee successful allocation, it has never been called wi=
th
>     __GFP_NOFAIL and threfore either should not be used for any rollbacks=
 or
>     should handle such errors correctly and not lead to critical failures=
.
> "
>
> If a significant kvmalloc operation is performed with the NOFAIL flag, it=
 risks
> reverting the fix intended to address the OOM-killer issue in commit
> dd544141b9eb.
> Should we indeed permit the NOFAIL flag for large kvmalloc allocations?

+ Vasily, Michal.

>
> >
> >                 if (nid =3D=3D NUMA_NO_NODE)
> > ---
> > This issue occurred during OPLUS KASAN test. Below is part of the log
> >
> > -> send signal
> > [65731.222840] [ T1308] oom-kill:constraint=3DCONSTRAINT_NONE,nodemask=
=3D(null),cpuset=3D/,mems_allowed=3D0,global_oom,task_memcg=3D/apps/uid_101=
98,task=3Dgs.intelligence,pid=3D32454,uid=3D10198
> >
> > [65731.259685] [T32454] Call trace:
> > [65731.259698] [T32454]  dump_backtrace+0xf4/0x118
> > [65731.259734] [T32454]  show_stack+0x18/0x24
> > [65731.259756] [T32454]  dump_stack_lvl+0x60/0x7c
> > [65731.259781] [T32454]  dump_stack+0x18/0x38
> > [65731.259800] [T32454]  mrdump_common_die+0x250/0x39c [mrdump]
> > [65731.259936] [T32454]  ipanic_die+0x20/0x34 [mrdump]
> > [65731.260019] [T32454]  atomic_notifier_call_chain+0xb4/0xfc
> > [65731.260047] [T32454]  notify_die+0x114/0x198
> > [65731.260073] [T32454]  die+0xf4/0x5b4
> > [65731.260098] [T32454]  die_kernel_fault+0x80/0x98
> > [65731.260124] [T32454]  __do_kernel_fault+0x160/0x2a8
> > [65731.260146] [T32454]  do_bad_area+0x68/0x148
> > [65731.260174] [T32454]  do_mem_abort+0x151c/0x1b34
> > [65731.260204] [T32454]  el1_abort+0x3c/0x5c
> > [65731.260227] [T32454]  el1h_64_sync_handler+0x54/0x90
> > [65731.260248] [T32454]  el1h_64_sync+0x68/0x6c
> > [65731.260269] [T32454]  z_erofs_decompress_queue+0x7f0/0x2258
> > --> be->decompressed_pages =3D kvcalloc(be->nr_pages, sizeof(struct pag=
e *), GFP_KERNEL | __GFP_NOFAIL);
> >         kernel panic by NULL pointer dereference.
> >         erofs assume kvmalloc with __GFP_NOFAIL never return NULL.
> >
> > [65731.260293] [T32454]  z_erofs_runqueue+0xf30/0x104c
> > [65731.260314] [T32454]  z_erofs_readahead+0x4f0/0x968
> > [65731.260339] [T32454]  read_pages+0x170/0xadc
> > [65731.260364] [T32454]  page_cache_ra_unbounded+0x874/0xf30
> > [65731.260388] [T32454]  page_cache_ra_order+0x24c/0x714
> > [65731.260411] [T32454]  filemap_fault+0xbf0/0x1a74
> > [65731.260437] [T32454]  __do_fault+0xd0/0x33c
> > [65731.260462] [T32454]  handle_mm_fault+0xf74/0x3fe0
> > [65731.260486] [T32454]  do_mem_abort+0x54c/0x1b34
> > [65731.260509] [T32454]  el0_da+0x44/0x94
> > [65731.260531] [T32454]  el0t_64_sync_handler+0x98/0xb4
> > [65731.260553] [T32454]  el0t_64_sync+0x198/0x19c
> >
> > --
> > 2.34.1
>
> Thanks
> Barry