From: Qu Wenruo wqu@suse.com
[ Upstream commit e0467866198f7f536806f39e5d0d91ae8018de08 ]
[BUG] When running generic/095, there is a high chance to crash with subpage data RW support:
assertion failed: PagePrivate(page) && page->private ------------[ cut here ]------------ kernel BUG at fs/btrfs/ctree.h:3403! Internal error: Oops - BUG: 0 [#1] SMP CPU: 1 PID: 3567 Comm: fio Tainted: 5.12.0-rc7-custom+ #17 Hardware name: Khadas VIM3 (DT) Call trace: assertfail.constprop.0+0x28/0x2c [btrfs] btrfs_subpage_assert+0x80/0xa0 [btrfs] btrfs_subpage_set_uptodate+0x34/0xec [btrfs] btrfs_page_clamp_set_uptodate+0x74/0xa4 [btrfs] btrfs_dirty_pages+0x160/0x270 [btrfs] btrfs_buffered_write+0x444/0x630 [btrfs] btrfs_direct_write+0x1cc/0x2d0 [btrfs] btrfs_file_write_iter+0xc0/0x160 [btrfs] new_sync_write+0xe8/0x180 vfs_write+0x1b4/0x210 ksys_pwrite64+0x7c/0xc0 __arm64_sys_pwrite64+0x24/0x30 el0_svc_common.constprop.0+0x70/0x140 do_el0_svc+0x28/0x90 el0_svc+0x2c/0x54 el0_sync_handler+0x1a8/0x1ac el0_sync+0x170/0x180 Code: f0000160 913be042 913c4000 955444bc (d4210000) ---[ end trace 3fdd39f4cccedd68 ]---
[CAUSE] Although prepare_pages() calls find_or_create_page(), which returns the page locked, but in later prepare_uptodate_page() calls, we may call btrfs_readpage() which will unlock the page before it returns.
This leaves a window where btrfs_releasepage() can sneak in and release the page, clearing page->private and causing above ASSERT().
[FIX] In prepare_uptodate_page(), we should not only check page->mapping, but also PagePrivate() to ensure we are still holding the correct page which has proper fs context setup.
Reported-by: Ritesh Harjani riteshh@linux.ibm.com Tested-by: Ritesh Harjani riteshh@linux.ibm.com Reviewed-by: Filipe Manana fdmanana@suse.com Signed-off-by: Qu Wenruo wqu@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/file.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index dd2504322a87..7798355098db 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1343,7 +1343,18 @@ static int prepare_uptodate_page(struct inode *inode, unlock_page(page); return -EIO; } - if (page->mapping != inode->i_mapping) { + + /* + * Since btrfs_readpage() will unlock the page before it + * returns, there is a window where btrfs_releasepage() can + * be called to release the page. + * Here we check both inode mapping and PagePrivate() to + * make sure the page was not released. + * + * The private flag check is essential for subpage as we need + * to store extra bitmap using page->private. + */ + if (page->mapping != inode->i_mapping || !PagePrivate(page)) { unlock_page(page); return -EAGAIN; }