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| author | Josef Bacik <josef@toxicpanda.com> | 2019-09-24 16:50:43 -0400 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2020-02-11 20:03:43 +0000 |
| commit | 2ce5f201744ae2245e6bd8587826a031789c6702 (patch) | |
| tree | 76b0d65b05a9c7606772a0b6a703108da8b4e04b | |
| parent | 9efc9109d30e41e9857bd11759a35ad0e0769784 (diff) | |
| download | linux-2ce5f201744ae2245e6bd8587826a031789c6702.tar.gz linux-2ce5f201744ae2245e6bd8587826a031789c6702.tar.bz2 linux-2ce5f201744ae2245e6bd8587826a031789c6702.zip | |
btrfs: check page->mapping when loading free space cache
commit 3797136b626ad4b6582223660c041efdea8f26b2 upstream.
While testing 5.2 we ran into the following panic
[52238.017028] BUG: kernel NULL pointer dereference, address: 0000000000000001
[52238.105608] RIP: 0010:drop_buffers+0x3d/0x150
[52238.304051] Call Trace:
[52238.308958] try_to_free_buffers+0x15b/0x1b0
[52238.317503] shrink_page_list+0x1164/0x1780
[52238.325877] shrink_inactive_list+0x18f/0x3b0
[52238.334596] shrink_node_memcg+0x23e/0x7d0
[52238.342790] ? do_shrink_slab+0x4f/0x290
[52238.350648] shrink_node+0xce/0x4a0
[52238.357628] balance_pgdat+0x2c7/0x510
[52238.365135] kswapd+0x216/0x3e0
[52238.371425] ? wait_woken+0x80/0x80
[52238.378412] ? balance_pgdat+0x510/0x510
[52238.386265] kthread+0x111/0x130
[52238.392727] ? kthread_create_on_node+0x60/0x60
[52238.401782] ret_from_fork+0x1f/0x30
The page we were trying to drop had a page->private, but had no
page->mapping and so called drop_buffers, assuming that we had a
buffer_head on the page, and then panic'ed trying to deref 1, which is
our page->private for data pages.
This is happening because we're truncating the free space cache while
we're trying to load the free space cache. This isn't supposed to
happen, and I'll fix that in a followup patch. However we still
shouldn't allow those sort of mistakes to result in messing with pages
that do not belong to us. So add the page->mapping check to verify that
we still own this page after dropping and re-acquiring the page lock.
This page being unlocked as:
btrfs_readpage
extent_read_full_page
__extent_read_full_page
__do_readpage
if (!nr)
unlock_page <-- nr can be 0 only if submit_extent_page
returns an error
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
[ add callchain ]
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
| -rw-r--r-- | fs/btrfs/free-space-cache.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c index be5f24c860d0..49c7c5344a0a 100644 --- a/fs/btrfs/free-space-cache.c +++ b/fs/btrfs/free-space-cache.c @@ -360,6 +360,12 @@ static int io_ctl_prepare_pages(struct io_ctl *io_ctl, struct inode *inode, if (uptodate && !PageUptodate(page)) { btrfs_readpage(NULL, page); lock_page(page); + if (page->mapping != inode->i_mapping) { + btrfs_err(BTRFS_I(inode)->root->fs_info, + "free space cache page truncated"); + io_ctl_drop_pages(io_ctl); + return -EIO; + } if (!PageUptodate(page)) { btrfs_err(BTRFS_I(inode)->root->fs_info, "error reading free space cache"); |