From b5bae2612af92fd8e7bcdcf7ce3e0259e8d341c9 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Fri, 14 Sep 2012 13:43:01 -0400 Subject: [PATCH] Btrfs: fix race when getting the eb out of page->private We can race when checking wether PagePrivate is set on a page and we actually have an eb saved in the pages private pointer. We could have easily written out this page and released it in the time that we did the pagevec lookup and actually got around to looking at this page. So use mapping->private_lock to ensure we get a consistent view of the page->private pointer. This is inline with the alloc and releasepage paths which use private_lock when manipulating page->private. Thanks, Reported-by: David Sterba Signed-off-by: Josef Bacik --- fs/btrfs/extent_io.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 90bd9f768c0a..a2c21570adf5 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -3256,19 +3256,34 @@ retry: break; } + spin_lock(&mapping->private_lock); + if (!PagePrivate(page)) { + spin_unlock(&mapping->private_lock); + continue; + } + eb = (struct extent_buffer *)page->private; + + /* + * Shouldn't happen and normally this would be a BUG_ON + * but no sense in crashing the users box for something + * we can survive anyway. + */ if (!eb) { + spin_unlock(&mapping->private_lock); WARN_ON(1); continue; } - if (eb == prev_eb) + if (eb == prev_eb) { + spin_unlock(&mapping->private_lock); continue; + } - if (!atomic_inc_not_zero(&eb->refs)) { - WARN_ON(1); + ret = atomic_inc_not_zero(&eb->refs); + spin_unlock(&mapping->private_lock); + if (!ret) continue; - } prev_eb = eb; ret = lock_extent_buffer_for_io(eb, fs_info, &epd); -- 2.20.1