Re: [PATCH] vmalloc: add warning in __vmalloc

[Minchan Kim]

On 05/03/2012 04:46 AM, Andrew Morton wrote:

> On Wed,  2 May 2012 13:28:09 +0900
> Minchan Kim <minchan@xxxxxxxxxx> wrote:
> 
>> Now there are several places to use __vmalloc with GFP_ATOMIC,
>> GFP_NOIO, GFP_NOFS but unfortunately __vmalloc calls map_vm_area
>> which calls alloc_pages with GFP_KERNEL to allocate page tables.
>> It means it's possible to happen deadlock.
>> I don't know why it doesn't have reported until now.
>>
>> Firstly, I tried passing gfp_t to lower functions to support __vmalloc
>> with such flags but other mm guys don't want and decided that
>> all of caller should be fixed.
>>
>> http://marc.info/?l=linux-kernel&m=133517143616544&w=2
>>
>> To begin with, let's listen other's opinion whether they can fix it
>> by other approach without calling __vmalloc with such flags.
>>
>> So this patch adds warning in __vmalloc_node_range to detect it and
>> to be fixed hopely. __vmalloc_node_range isn't random chocie because
>> all caller which has gfp_mask of map_vm_area use it through __vmalloc_area_node.
>> And __vmalloc_area_node is current static function and is called by only
>> __vmalloc_node_range. So warning in __vmalloc_node_range would cover all
>> vmalloc functions which have gfp_t argument.
>>
>> I Cced related maintainers.
>> If I miss someone, please Cced them.
>>
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -1648,6 +1648,10 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
>>  	void *addr;
>>  	unsigned long real_size = size;
>>  
>> +	WARN_ON_ONCE(!(gfp_mask & __GFP_WAIT) ||
>> +			!(gfp_mask & __GFP_IO) ||
>> +			!(gfp_mask & __GFP_FS));
>> +
>>  	size = PAGE_ALIGN(size);
>>  	if (!size || (size >> PAGE_SHIFT) > totalram_pages)
>>  		goto fail;
> 
> Well.  What are we actually doing here?  Causing the kernel to spew a
> warning due to known-buggy callsites, so that users will report the
> warnings, eventually goading maintainers into fixing their stuff.
> 
> This isn't very efficient :(


Yes. I hope maintainers fix it before merging this.

> 
> It would be better to fix that stuff first, then add the warning to
> prevent reoccurrences.  Yes, maintainers are very naughty and probably
> do need cattle prods^W^W warnings to motivate them to fix stuff, but we
> should first make an effort to get these things fixed without
> irritating and alarming our users.  
> 
> Where are these offending callsites?


dm:
__alloc_buffer_wait_no_callback

ubi:
ubi_dbg_check_write
ubi_dbg_check_all_ff

ext4 :
ext4_kvmalloc

gfs2 :
gfs2_alloc_sort_buffer

ntfs :
__ntfs_malloc

ubifs :
dbg_dump_leb
scan_check_cb
dump_lpt_leb
dbg_check_ltab_lnum
dbg_scan_orphans

mm :
alloc_large_system_hash

ceph :
fill_inode
ceph_setxattr
ceph_removexattr
ceph_x_build_authorizer
ceph_decode_buffer
ceph_alloc_middle



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-- 
Kind regards,
Minchan Kim
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