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authorOmar Sandoval <osandov@osandov.com>2015-02-24 02:47:05 -0800
committerChris Mason <clm@fb.com>2015-04-26 06:27:00 -0700
commit5ca64f45e92dc52bd3bc1ad93f4f9e5a57955f28 (patch)
tree3e197015904be5b68c3ed94314c4ca2ef0c06051 /fs
parent67b7859e9bfa0dcee5a8256932e393e98739be1b (diff)
downloadlinux-5ca64f45e92dc52bd3bc1ad93f4f9e5a57955f28.tar.bz2
btrfs: fix race on ENOMEM in alloc_extent_buffer
Consider the following interleaving of overlapping calls to alloc_extent_buffer: Call 1: - Successfully allocates a few pages with find_or_create_page - find_or_create_page fails, goto free_eb - Unlocks the allocated pages Call 2: - Calls find_or_create_page and gets a page in call 1's extent_buffer - Finds that the page is already associated with an extent_buffer - Grabs a reference to the half-written extent_buffer and calls mark_extent_buffer_accessed on it mark_extent_buffer_accessed will then try to call mark_page_accessed on a null page and panic. The fix is to decrement the reference count on the half-written extent_buffer before unlocking the pages so call 2 won't use it. We should also set exists = NULL in the case that we don't use exists to avoid accidentally returning a freed extent_buffer in an error case. Signed-off-by: Omar Sandoval <osandov@osandov.com> Reviewed-by: David Sterba <dsterba@suse.cz> Reviewed-by: Liu Bo <bo.li.liu@oracle.com> Signed-off-by: Chris Mason <clm@fb.com>
Diffstat (limited to 'fs')
-rw-r--r--fs/btrfs/extent_io.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 782f3bc4651d..ea100eb188de 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4870,6 +4870,7 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
mark_extent_buffer_accessed(exists, p);
goto free_eb;
}
+ exists = NULL;
/*
* Do this so attach doesn't complain and we need to
@@ -4933,12 +4934,12 @@ again:
return eb;
free_eb:
+ WARN_ON(!atomic_dec_and_test(&eb->refs));
for (i = 0; i < num_pages; i++) {
if (eb->pages[i])
unlock_page(eb->pages[i]);
}
- WARN_ON(!atomic_dec_and_test(&eb->refs));
btrfs_release_extent_buffer(eb);
return exists;
}