On Fri, Dec 21, 2012 at 4:36 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Thu, Dec 20, 2012 at 4:49 PM, Michel Lespinasse <walken@xxxxxxxxxx> wrote:
>> We have many vma manipulation functions that are fast in the typical case,
>> but can optionally be instructed to populate an unbounded number of ptes
>> within the region they work on:
>> - mmap with MAP_POPULATE or MAP_LOCKED flags;
>> - remap_file_pages() with MAP_NONBLOCK not set or when working on a
>> VM_LOCKED vma;
>> - mmap_region() and all its wrappers when mlock(MCL_FUTURE) is in effect;
>> - brk() when mlock(MCL_FUTURE) is in effect.
>>
>
> Something's buggy here. My evil test case is stuck with lots of
> threads spinning at 100% system time. Stack traces look like:
>
> [<0000000000000000>] __mlock_vma_pages_range+0x66/0x70
> [<0000000000000000>] __mm_populate+0xf9/0x150
> [<0000000000000000>] vm_mmap_pgoff+0x9f/0xc0
> [<0000000000000000>] sys_mmap_pgoff+0x7e/0x150
> [<0000000000000000>] sys_mmap+0x22/0x30
> [<0000000000000000>] system_call_fastpath+0x16/0x1b
> [<0000000000000000>] 0xffffffffffffffff
>
> perf top says:
>
> 38.45% [kernel] [k] __mlock_vma_pages_range
> 33.04% [kernel] [k] __get_user_pages
> 28.18% [kernel] [k] __mm_populate
>
> The tasks in question use MCL_FUTURE but not MAP_POPULATE. These
> tasks are immune to SIGKILL.
Looking into it.
There seems to be a problem with mlockall - the following program
fails in an unkillable way even before my changes:
#include <sys/mman.h>
#include <stdio.h>
#include <stdint.h>
int main(void) {
void *p = mmap(NULL, 0x100000000000,
PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANON | MAP_NORESERVE,
-1, 0);
printf("p: %p\n", p);
mlockall(MCL_CURRENT);
return 0;
}
I think my changes propagate this existing problem so it now shows up
in more places :/
--
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>