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[PATCH] mm: fix madvise vma merging 

Better late than never, I've at last reviewed the madvise vma merging
going into 2.6.13.  Remove a pointless check and fix two little bugs -
a simple test (with /proc/<pid>/maps hacked to show ReadHints) showed
both mismerges in practice: though being madvise, neither was disastrous.

1. Correct placement of the success label in madvise_behavior: as in
   mprotect_fixup and mlock_fixup, it is necessary to update vm_flags
   when vma_merge succeeds (to handle the exceptional Case 8 noted in
   the comments above vma_merge itself).

2. Correct initial value of prev when starting part way into a vma: as
   in sys_mprotect and do_mlock, it needs to be set to vma in this case
   (vma_merge handles only that minimum of cases shown in its comments).

3. If find_vma_prev sets prev, then the vma it returns is prev->vm_next,
   so it's pointless to make that same assignment again in sys_madvise.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Hugh Dickins 2005-09-03 15:54:53 -07:00 committed by Linus Torvalds
parent 53e9a6159f
commit 836d5ffd34
1 changed files with 5 additions and 4 deletions
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9
mm/madvise.c
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@ -37,7 +37,7 @@ static long madvise_behavior(struct vm_area_struct * vma,
if (new_flags == vma->vm_flags) { if (new_flags == vma->vm_flags) {
*prev = vma; *prev = vma;
goto success; goto out;
} }
pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT); pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
@ -62,6 +62,7 @@ static long madvise_behavior(struct vm_area_struct * vma,
goto out; goto out;
} }
success:
/* /*
* vm_flags is protected by the mmap_sem held in write mode. * vm_flags is protected by the mmap_sem held in write mode.
*/ */
@ -70,7 +71,6 @@ static long madvise_behavior(struct vm_area_struct * vma,
out: out:
if (error == -ENOMEM) if (error == -ENOMEM)
error = -EAGAIN; error = -EAGAIN;
success:
return error; return error;
} }
@ -237,8 +237,9 @@ asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
* - different from the way of handling in mlock etc. * - different from the way of handling in mlock etc.
*/ */
vma = find_vma_prev(current->mm, start, &prev); vma = find_vma_prev(current->mm, start, &prev);
if (!vma && prev) if (vma && start > vma->vm_start)
vma = prev->vm_next; prev = vma;
for (;;) { for (;;) {
/* Still start < end. */ /* Still start < end. */
error = -ENOMEM; error = -ENOMEM;