On Thu, May 9, 2024 at 12:58 AM <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>
---
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?