Messages in this thread | | | Date | Wed, 8 May 2024 23:10:46 +0800 | Subject | Re: [RFC PATCH] mm/vmalloc: fix vmalloc which may return null if called with __GFP_NOFAIL | From | Gao Xiang <> |
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Hi,
On 2024/5/8 22:43, Hailong Liu wrote: > On Wed, 08. May 21:41, Gao Xiang wrote: >> >> +Cc Michal, >> >> On 2024/5/8 20:58, 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> >> >> Why taging this as RFC here? It seems a corner-case fix of >> commit a421ef303008 >> >> Thanks, >> Gao Xiang >> > > Hi Gao Xiang: > > RFC here to wait for a better way to handle this case :). > IMO, if vmalloc support __GFP_NOFAIL it should not return > null even system is deadlock on memory.
The starting point is that kmalloc doesn't support __GFP_NOFAIL if order > 1 (even for very short temporary uses), see: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/page_alloc.c?h=v6.8#n2896
but it is possible if we have such page pointer array (since two (order-1) pages can only keep 1024 8-byte entries, it can happen if compression ratios are high), and kvmalloc(__GFP_NOFAIL) has already been supported for almost two years, it will fallback to order-0 allocation as described in commit e9c3cda4d86e ("mm, vmalloc: fix high order __GFP_NOFAIL allocations").
With my limited understanding, I'm not sure why it can cause deadlock here since it will fallback to order-0 allocation then, and such allocation is just for short temporary uses again because kmalloc doesn't support order > 1 short memory allocation strictly.
Thanks, Gao Xiang
> > -- > > Best Regards, > Hailong.
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