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 <[email protected]>
--- 2.6.13-rc5-git3/mm/madvise.c 2005-08-02 12:07:23.000000000 +0100
+++ linux/mm/madvise.c 2005-08-05 18:06:47.000000000 +0100
@@ -37,7 +37,7 @@ static long madvise_behavior(struct vm_a
if (new_flags == vma->vm_flags) {
*prev = vma;
- goto success;
+ goto out;
}
pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
@@ -62,6 +62,7 @@ static long madvise_behavior(struct vm_a
goto out;
}
+success:
/*
* vm_flags is protected by the mmap_sem held in write mode.
*/
@@ -70,7 +71,6 @@ static long madvise_behavior(struct vm_a
out:
if (error == -ENOMEM)
error = -EAGAIN;
-success:
return error;
}
@@ -237,8 +237,9 @@ asmlinkage long sys_madvise(unsigned lon
* - different from the way of handling in mlock etc.
*/
vma = find_vma_prev(current->mm, start, &prev);
- if (!vma && prev)
- vma = prev->vm_next;
+ if (vma && start > vma->vm_start)
+ prev = vma;
+
for (;;) {
/* Still start < end. */
error = -ENOMEM;
-
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