Re: [v2 PATCH 2/2 -mm] mm: brk: dwongrade mmap_sem to read when shrinking

[Vlastimil Babka]

On 9/27/18 2:50 PM, Kirill A. Shutemov wrote:
>> diff --git a/mm/mmap.c b/mm/mmap.c
>> index 017bcfa..0d2fae1 100644
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -193,9 +193,11 @@ static int do_brk_flags(unsigned long addr, unsigned long request, unsigned long
>>  	unsigned long retval;
>>  	unsigned long newbrk, oldbrk;
>>  	struct mm_struct *mm = current->mm;
>> +	unsigned long origbrk = mm->brk;
> 
> Is it safe to read mm->brk outside the lock?

Good catch! I guess not, parallel brk()'s could then race.