Re: [PATCH] mm: mmap: show vm_unmapped_area error log

[Jaewon Kim]

Hello

sorry for build warning.
I've changed %d to %ld reported by kbuild.
Let me attach full patch again below.
--------------------------------------------------


Even on 64 bit kernel, the mmap failure can happen for a 32 bit task.
Virtual memory space shortage of a task on mmap is reported to userspace
as -ENOMEM. It can be confused as physical memory shortage of overall
system.

The vm_unmapped_area can be called to by some drivers or other kernel
core system like filesystem. It can be hard to know which code layer
returns the -ENOMEM.

Print error log of vm_unmapped_area with rate limited. Without rate
limited, soft lockup ocurrs on infinite mmap sytem call.

i.e.)
<3>[  576.024088]  [6:  mmap_infinite:14251] mmap: vm_unmapped_area err:-12 total_vm:0xfee08 flags:0x1 len:0xa00000 low:0x8000 high:0xf3f63000

Fixed type mismatching on previous patch which is reported by kbuild.
Reported-by: kbuild test robot <lkp@xxxxxxxxx>

Signed-off-by: Jaewon Kim <jaewon31.kim@xxxxxxxxxxx>
---
 include/linux/mm.h | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 52269e56c514..ecf9e1fcde79 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2379,10 +2379,19 @@ extern unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info);
 static inline unsigned long
 vm_unmapped_area(struct vm_unmapped_area_info *info)
 {
+    unsigned long addr;
+
     if (info->flags & VM_UNMAPPED_AREA_TOPDOWN)
-        return unmapped_area_topdown(info);
+        addr = unmapped_area_topdown(info);
     else
-        return unmapped_area(info);
+        addr = unmapped_area(info);
+
+    if (IS_ERR_VALUE(addr) && printk_ratelimit()) {
+        pr_err("%s err:%ld total_vm:0x%lx flags:0x%lx len:0x%lx low:0x%lx high:0x%lx\n",
+            __func__, addr, current->mm->total_vm, info->flags,
+            info->length, info->low_limit, info->high_limit);
+    }
+    return addr;
 }



On 2020ë 03ì 04ì 12:02, Jaewon Kim wrote:
> Even on 64 bit kernel, the mmap failure can happen for a 32 bit task.
> Virtual memory space shortage of a task on mmap is reported to userspace
> as -ENOMEM. It can be confused as physical memory shortage of overall
> system.
>
> The vm_unmapped_area can be called to by some drivers or other kernel
> core system like filesystem. It can be hard to know which code layer
> returns the -ENOMEM.
>
> Print error log of vm_unmapped_area with rate limited. Without rate
> limited, soft lockup ocurrs on infinite mmap sytem call.
>
> i.e.)
> <3>[  576.024088]  [6:  mmap_infinite:14251] mmap: vm_unmapped_area err:-12 total_vm:0xfee08 flags:0x1 len:0xa00000 low:0x8000 high:0xf3f63000
>
> Signed-off-by: Jaewon Kim <jaewon31.kim@xxxxxxxxxxx>
> ---
>  include/linux/mm.h | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 52269e56c514..ee822d65ebb7 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2379,10 +2379,19 @@ extern unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info);
>  static inline unsigned long
>  vm_unmapped_area(struct vm_unmapped_area_info *info)
>  {
> +	unsigned long addr;
> +
>  	if (info->flags & VM_UNMAPPED_AREA_TOPDOWN)
> -		return unmapped_area_topdown(info);
> +		addr = unmapped_area_topdown(info);
>  	else
> -		return unmapped_area(info);
> +		addr = unmapped_area(info);
> +
> +	if (IS_ERR_VALUE(addr) && printk_ratelimit()) {
> +		pr_err("%s err:%d total_vm:0x%lx flags:0x%lx len:0x%lx low:0x%lx high:0x%lx\n",
> +			__func__, addr, current->mm->total_vm, info->flags,
> +			info->length, info->low_limit, info->high_limit);
> +	}
> +	return addr;
>  }
>  
>  /* truncate.c */