On Wed 05-07-17 20:53:02, Michal Hocko wrote:
> On Wed 05-07-17 11:35:51, Linus Torvalds wrote:
> > On Wed, Jul 5, 2017 at 11:28 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> > >
> > > Dohh, that was on mmotm which has a clean up by Oleg which reorganizes
> > > the code a bit. This is on top of the current master
> >
> > Oh, ok. I think I know which patch from Oleg you're talking about.
> >
> > Since I do want that patch too, and since I'd hate to cause
> > unnecessary merge conflicts in this area, how about we just plan on
> > letting your original patch (on top of Oleg's) go through Andrew and
> > the -mm tree? I'll get it that way, and it's not like this is
> > timing-critical.
>
> That would lead to conflicts when backporting to stable trees though
> which is quite annoying as well and arguably slightly more annoying than
> resolving this in mmotm. I can help to rebase Oleg's patch on top of
> mine which is not a stable material.
Here is the rebase of Oleg's patch.
---
>From 61ff0cd972dac218390a5859b89ce386db731d1d Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Date: Fri, 30 Jun 2017 10:19:00 +0200
Subject: [PATCH] mm/mmap.c: expand_downwards: don't require the gap if
!vm_prev
expand_stack(vma) fails if address < stack_guard_gap even if there is no
vma->vm_prev. I don't think this makes sense, and we didn't do this
before the recent commit 1be7107fbe18 ("mm: larger stack guard gap,
between vmas"). We do not need a gap in this case, any address is fine as
long as security_mmap_addr() doesn't object.
This also simplifies the code, we know that address >= prev->vm_end and
thus underflow is not possible.
Link: http://lkml.kernel.org/r/20170628175258.GA24881@xxxxxxxxxx
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Larry Woodman <lwoodman@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
mm/mmap.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index ece0f6d3a1b5..f30847405cab 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2316,7 +2316,6 @@ int expand_downwards(struct vm_area_struct *vma,
{
struct mm_struct *mm = vma->vm_mm;
struct vm_area_struct *prev;
- unsigned long gap_addr;
int error;
address &= PAGE_MASK;
@@ -2325,15 +2324,12 @@ int expand_downwards(struct vm_area_struct *vma,
return error;
/* Enforce stack_guard_gap */
- gap_addr = address - stack_guard_gap;
- if (gap_addr > address)
- return -ENOMEM;
prev = vma->vm_prev;
- if (prev && prev->vm_end > gap_addr &&
+ /* Check that both stack segments have the same anon_vma? */
+ if (prev && !(prev->vm_flags & VM_GROWSDOWN) &&
(prev->vm_flags & (VM_WRITE|VM_READ|VM_EXEC))) {
- if (!(prev->vm_flags & VM_GROWSDOWN))
+ if (address - prev->vm_end < stack_guard_gap)
return -ENOMEM;
- /* Check that both stack segments have the same anon_vma? */
}
/* We must make sure the anon_vma is allocated. */
--
2.11.0
--
Michal Hocko
SUSE Labs
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