Re: [RFC PATCH] mm/vmalloc: fix vmalloc which may return null if called with __GFP_NOFAIL

[Barry Song <21cnbao@gmail.com>]

On Thu, May 9, 2024 at 12:58 AM <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(current))
>                         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: vmalloc
    does not guarantee successful allocation, it has never been called with
    __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?

>
>                 if (nid == NUMA_NO_NODE)
> ---
> This issue occurred during OPLUS KASAN test. Below is part of the log
>
> -> send signal
> [65731.222840] [ T1308] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/apps/uid_10198,task=gs.intelligence,pid=32454,uid=10198
>
> [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 = kvcalloc(be->nr_pages, sizeof(struct page *), 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