Commit 836d5ffd authored Sep 03, 2005 by Hugh Dickins Committed by Linus Torvalds Sep 05, 2005

[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>

parent 53e9a615

mm/madvise.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -37,7 +37,7 @@ static long madvise_behavior(struct vm_area_struct * vma,

		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_area_struct * vma,
		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_area_struct * vma,
		out:
		if (error == -ENOMEM)
		error = -EAGAIN;
		success:
		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.
		*/
		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;