From: Omar Sandoval Date: Tue, 24 Feb 2015 10:47:05 +0000 (-0800) Subject: btrfs: fix race on ENOMEM in alloc_extent_buffer X-Git-Tag: v4.1-rc2~10^2~4 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=5ca64f45e92dc52bd3bc1ad93f4f9e5a57955f28;p=profile%2Fcommon%2Fplatform%2Fkernel%2Flinux-artik7.git 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 Reviewed-by: David Sterba Reviewed-by: Liu Bo Signed-off-by: Chris Mason --- diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 782f3bc..ea100eb 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; }