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SubjectRe: [PATCH] Don't mlock guardpage if the stack is growing up
On Mon, May 9, 2011 at 4:12 AM, Mikulas Patocka
<mikulas@artax.karlin.mff.cuni.cz> wrote:
>
> See ./lib/mm/memlock.c in LVM2. It reads /proc/self/maps, parses the file
> and locks each map with mlock, except for glibc locale file.

Hmm. One thing that strikes me is this problem also implies that the
/proc/self/maps file is wrong for the GROWSUP case, isn't it?

So I think we should not just apply your lock fix, but then *also*
apply something like this:

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 2e7addfd9803..080980880c7f 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -214,7 +214,7 @@ static void show_map_vma(struct seq_file *m,
struct vm_area_struct *vma)
int flags = vma->vm_flags;
unsigned long ino = 0;
unsigned long long pgoff = 0;
- unsigned long start;
+ unsigned long start, end;
dev_t dev = 0;
int len;

@@ -227,13 +227,16 @@ static void show_map_vma(struct seq_file *m,
struct vm_area_struct *vma)

/* We don't show the stack guard page in /proc/maps */
start = vma->vm_start;
- if (vma->vm_flags & VM_GROWSDOWN)
- if (!vma_stack_continue(vma->vm_prev, vma->vm_start))
- start += PAGE_SIZE;
+ if (stack_guard_page_growsdown(vma, start))
+ start += PAGE_SIZE;
+ end = vma->vm_end;
+ if (stack_guard_page_growsup(vma, end))
+ end -= PAGE_SIZE;
+

seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
start,
- vma->vm_end,
+ end,
flags & VM_READ ? 'r' : '-',
flags & VM_WRITE ? 'w' : '-',
flags & VM_EXEC ? 'x' : '-',

NOTE! The above actually assumes that your
"stack_guard_page_growsup()" has been changed to actually take the
"next page" value, which I think makes more sense (ie it's the "end of
stack", the same way "stack_guard_page_growsdown()" address is).

Hmm? I don't have any growsup machine to test with, can you do that?

Linus


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