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@xxxxxxxx wrote:
From: "Hailong.Liu" <hailong.liu@xxxxxxxx>
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@xxxxxxxx>
Signed-off-by: Hailong.Liu <hailong.liu@xxxxxxxx>
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.
