diff options
authorJeremy Fitzhardinge <jeremy@goop.org>2009-02-11 13:04:41 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2009-02-11 14:25:37 -0800
commit9480c53e9b2aa13a06283ffb96bb8f1873ac4e9a (patch)
parent3abdbf90a3ffb006108c831c56b092e35483b6ec (diff)
mm: rearrange exit_mmap() to unlock before arch_exit_mmap
Christophe Saout reported [in precursor to: http://marc.info/?l=linux-kernel&m=123209902707347&w=4]: > Note that I also some a different issue with CONFIG_UNEVICTABLE_LRU. > Seems like Xen tears down current->mm early on process termination, so > that __get_user_pages in exit_mmap causes nasty messages when the > process had any mlocked pages. (in fact, it somehow manages to get into > the swapping code and produces a null pointer dereference trying to get > a swap token) Jeremy explained: Yes. In the normal case under Xen, an in-use pagetable is "pinned", meaning that it is RO to the kernel, and all updates must go via hypercall (or writes are trapped and emulated, which is much the same thing). An unpinned pagetable is not currently in use by any process, and can be directly accessed as normal RW pages. As an optimisation at process exit time, we unpin the pagetable as early as possible (switching the process to init_mm), so that all the normal pagetable teardown can happen with direct memory accesses. This happens in exit_mmap() -> arch_exit_mmap(). The munlocking happens a few lines below. The obvious thing to do would be to move arch_exit_mmap() to below the munlock code, but I think we'd want to call it even if mm->mmap is NULL, just to be on the safe side. Thus, this patch: exit_mmap() needs to unlock any locked vmas before calling arch_exit_mmap, as the latter may switch the current mm to init_mm, which would cause the former to fail. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com> Cc: Christophe Saout <christophe@saout.de> Cc: Keir Fraser <keir.fraser@eu.citrix.com> Cc: Christophe Saout <christophe@saout.de> Cc: Alex Williamson <alex.williamson@hp.com> Cc: <stable@kernel.org> [2.6.28.x] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 6 insertions, 4 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index eb1270bebe67..00ced3ee49a8 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2084,12 +2084,8 @@ void exit_mmap(struct mm_struct *mm)
unsigned long end;
/* mm's last user has gone, and its about to be pulled down */
- arch_exit_mmap(mm);
- if (!mm->mmap) /* Can happen if dup_mmap() received an OOM */
- return;
if (mm->locked_vm) {
vma = mm->mmap;
while (vma) {
@@ -2098,7 +2094,13 @@ void exit_mmap(struct mm_struct *mm)
vma = vma->vm_next;
+ arch_exit_mmap(mm);
vma = mm->mmap;
+ if (!vma) /* Can happen if dup_mmap() received an OOM */
+ return;
tlb = tlb_gather_mmu(mm, 1);