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| author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2010-10-27 15:32:58 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-10-27 18:03:05 -0700 |
| commit | 20273941f2129aa5a432796d98a276ed73d60782 (patch) | |
| tree | 85da0d951ac10f239f81ad7f69559fdeb692095b /arch/frv | |
| parent | a8e23a291852cd7c4fb5ca696dbb93912185ad10 (diff) | |
| download | lwn-20273941f2129aa5a432796d98a276ed73d60782.tar.gz lwn-20273941f2129aa5a432796d98a276ed73d60782.zip | |
mm: fix race in kunmap_atomic()
Christoph reported a nice splat which illustrated a race in the new stack
based kmap_atomic implementation.
The problem is that we pop our stack slot before we're completely done
resetting its state -- in particular clearing the PTE (sometimes that's
CONFIG_DEBUG_HIGHMEM). If an interrupt happens before we actually clear
the PTE used for the last slot, that interrupt can reuse the slot in a
dirty state, which triggers a BUG in kmap_atomic().
Fix this by introducing kmap_atomic_idx() which reports the current slot
index without actually releasing it and use that to find the PTE and delay
the _pop() until after we're completely done.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reported-by: Christoph Hellwig <hch@infradead.org>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch/frv')
| -rw-r--r-- | arch/frv/mm/highmem.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/arch/frv/mm/highmem.c b/arch/frv/mm/highmem.c index 61088dcc1594..fd7fcd4c2e33 100644 --- a/arch/frv/mm/highmem.c +++ b/arch/frv/mm/highmem.c @@ -68,7 +68,7 @@ EXPORT_SYMBOL(__kmap_atomic); void __kunmap_atomic(void *kvaddr) { - int type = kmap_atomic_idx_pop(); + int type = kmap_atomic_idx(); switch (type) { case 0: __kunmap_atomic_primary(4, 6); break; case 1: __kunmap_atomic_primary(5, 7); break; @@ -83,6 +83,7 @@ void __kunmap_atomic(void *kvaddr) default: BUG(); } + kmap_atomic_idx_pop(); pagefault_enable(); } EXPORT_SYMBOL(__kunmap_atomic); |