The patch titled
Subject: mm: protect against concurrent vma expansion
has been removed from the -mm tree. Its filename was
mm-protect-against-concurrent-vma-expansion.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Michel Lespinasse <walken@xxxxxxxxxx>
Subject: mm: protect against concurrent vma expansion
expand_stack() runs with a shared mmap_sem lock. Because of this, there
could be multiple concurrent stack expansions in the same mm, which may
cause problems in the vma gap update code.
I propose to solve this by taking the mm->page_table_lock around such vma
expansions, in order to avoid the concurrency issue. We only have to
worry about concurrent expand_stack() calls here, since we hold a shared
mmap_sem lock and all vma modificaitons other than expand_stack() are done
under an exclusive mmap_sem lock.
I previously tried to achieve the same effect by making sure all growable
vmas in a given mm would share the same anon_vma, which we already lock
here. However this turned out to be difficult - all of the schemes I
tried for refcounting the growable anon_vma and clearing turned out ugly.
So, I'm now proposing only the minimal fix.
The overhead of taking the page table lock during stack expansion is
expected to be small: glibc doesn't use expandable stacks for the threads
it creates, so having multiple growable stacks is actually uncommon and we
don't expect the page table lock to get bounced between threads.
Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mmap.c | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)
diff -puN mm/mmap.c~mm-protect-against-concurrent-vma-expansion mm/mmap.c
--- a/mm/mmap.c~mm-protect-against-concurrent-vma-expansion
+++ a/mm/mmap.c
@@ -2069,6 +2069,18 @@ int expand_upwards(struct vm_area_struct
if (vma->vm_pgoff + (size >> PAGE_SHIFT) >= vma->vm_pgoff) {
error = acct_stack_growth(vma, size, grow);
if (!error) {
+ /*
+ * vma_gap_update() doesn't support concurrent
+ * updates, but we only hold a shared mmap_sem
+ * lock here, so we need to protect against
+ * concurrent vma expansions.
+ * vma_lock_anon_vma() doesn't help here, as
+ * we don't guarantee that all growable vmas
+ * in a mm share the same root anon vma.
+ * So, we reuse mm->page_table_lock to guard
+ * against concurrent vma expansions.
+ */
+ spin_lock(&vma->vm_mm->page_table_lock);
anon_vma_interval_tree_pre_update_vma(vma);
vma->vm_end = address;
anon_vma_interval_tree_post_update_vma(vma);
@@ -2076,6 +2088,8 @@ int expand_upwards(struct vm_area_struct
vma_gap_update(vma->vm_next);
else
vma->vm_mm->highest_vm_end = address;
+ spin_unlock(&vma->vm_mm->page_table_lock);
+
perf_event_mmap(vma);
}
}
@@ -2126,11 +2140,25 @@ int expand_downwards(struct vm_area_stru
if (grow <= vma->vm_pgoff) {
error = acct_stack_growth(vma, size, grow);
if (!error) {
+ /*
+ * vma_gap_update() doesn't support concurrent
+ * updates, but we only hold a shared mmap_sem
+ * lock here, so we need to protect against
+ * concurrent vma expansions.
+ * vma_lock_anon_vma() doesn't help here, as
+ * we don't guarantee that all growable vmas
+ * in a mm share the same root anon vma.
+ * So, we reuse mm->page_table_lock to guard
+ * against concurrent vma expansions.
+ */
+ spin_lock(&vma->vm_mm->page_table_lock);
anon_vma_interval_tree_pre_update_vma(vma);
vma->vm_start = address;
vma->vm_pgoff -= grow;
anon_vma_interval_tree_post_update_vma(vma);
vma_gap_update(vma);
+ spin_unlock(&vma->vm_mm->page_table_lock);
+
perf_event_mmap(vma);
}
}
_
Patches currently in -mm which might be from walken@xxxxxxxxxx are
origin.patch
linux-next.patch
lib-rbtree_testc-fix-uninitialized-variable-warning.patch
random32-rename-random32-to-prandom.patch
prandom-introduce-prandom_bytes-and-prandom_bytes_state.patch
bnx2x-use-prandom_bytes.patch
mtd-nandsim-use-prandom_bytes.patch
ubifs-use-prandom_bytes.patch
mtd-mtd_nandecctest-use-prandom_bytes-instead-of-get_random_bytes.patch
mtd-mtd_oobtest-convert-to-use-prandom-library.patch
mtd-mtd_pagetest-convert-to-use-prandom-library.patch
mtd-mtd_speedtest-use-prandom_bytes.patch
mtd-mtd_subpagetest-convert-to-use-prandom-library.patch
mtd-mtd_stresstest-use-prandom_bytes.patch
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