[PATCH AUTOSEL 6.0 24/32] f2fs: fix wrong dirty page count when race between mmap and fallocate.

Sasha Levin
2022-10-18T00:11:10Z

From: Shuqi Zhang <zhangshuqi3@huawei.com>

[ Upstream commit 9b7eadd9bd3a0cc24533a23d83c46430a0ea60ff ]

This is a BUG_ON issue as follows when running xfstest-generic-503:
WARNING: CPU: 21 PID: 1385 at fs/f2fs/inode.c:762 f2fs_evict_inode+0x847/0xaa0
Modules linked in:
CPU: 21 PID: 1385 Comm: umount Not tainted 5.19.0-rc5+ #73
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014

Call Trace:
evict+0x129/0x2d0
dispose_list+0x4f/0xb0
evict_inodes+0x204/0x230
generic_shutdown_super+0x5b/0x1e0
kill_block_super+0x29/0x80
kill_f2fs_super+0xe6/0x140
deactivate_locked_super+0x44/0xc0
deactivate_super+0x79/0x90
cleanup_mnt+0x114/0x1a0
__cleanup_mnt+0x16/0x20
task_work_run+0x98/0x100
exit_to_user_mode_prepare+0x3d0/0x3e0
syscall_exit_to_user_mode+0x12/0x30
do_syscall_64+0x42/0x80
entry_SYSCALL_64_after_hwframe+0x46/0xb0

Function flow analysis when BUG occurs:
f2fs_fallocate mmap
do_page_fault
pte_spinlock // ---lock_pte
do_wp_page
wp_page_shared
pte_unmap_unlock // unlock_pte
do_page_mkwrite
f2fs_vm_page_mkwrite
down_read(invalidate_lock)
lock_page
if (PageMappedToDisk(page))
goto out;
// set_page_dirty --NOT RUN
out: up_read(invalidate_lock);
finish_mkwrite_fault // unlock_pte
f2fs_collapse_range
down_write(i_mmap_sem)
truncate_pagecache
unmap_mapping_pages
i_mmap_lock_write // down_write(i_mmap_rwsem)
......
zap_pte_range
pte_offset_map_lock // ---lock_pte
set_page_dirty
f2fs_dirty_data_folio
if (!folio_test_dirty(folio)) {
fault_dirty_shared_page
set_page_dirty
f2fs_dirty_data_folio
if (!folio_test_dirty(folio)) {
filemap_dirty_folio
f2fs_update_dirty_folio // ++
}
unlock_page
filemap_dirty_folio
f2fs_update_dirty_folio // page count++
}
pte_unmap_unlock // --unlock_pte
i_mmap_unlock_write // up_write(i_mmap_rwsem)
truncate_inode_pages
up_write(i_mmap_sem)

When race happens between mmap-do_page_fault-wp_page_shared and
fallocate-truncate_pagecache-zap_pte_range, the zap_pte_range calls
function set_page_dirty without page lock. Besides, though
truncate_pagecache has immap and pte lock, wp_page_shared calls
fault_dirty_shared_page without any. In this case, two threads race
in f2fs_dirty_data_folio function. Page is set to dirty only ONCE,
but the count is added TWICE by calling filemap_dirty_folio.
Thus the count of dirty page cannot accord with the real dirty pages.

Following is the solution to in case of race happens without any lock.
Since folio_test_set_dirty in filemap_dirty_folio is atomic, judge return
value will not be at risk of race.

Signed-off-by: Shuqi Zhang <zhangshuqi3@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/f2fs/checkpoint.c | 3 +--
fs/f2fs/data.c | 3 +--
fs/f2fs/node.c | 3 +--
3 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 8259e0fa97e1..3a3329bf1033 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -448,8 +448,7 @@ static bool f2fs_dirty_meta_folio(struct address_space *mapping,

if (!folio_test_uptodate(folio))
folio_mark_uptodate(folio);
- if (!folio_test_dirty(folio)) {
- filemap_dirty_folio(mapping, folio);
+ if (filemap_dirty_folio(mapping, folio)) {
inc_page_count(F2FS_M_SB(mapping), F2FS_DIRTY_META);
set_page_private_reference(&folio->page);
return true;
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index aa3ccddfa037..16c39bd948a0 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -3697,8 +3697,7 @@ static bool f2fs_dirty_data_folio(struct address_space *mapping,
folio_mark_uptodate(folio);
BUG_ON(folio_test_swapcache(folio));

- if (!folio_test_dirty(folio)) {
- filemap_dirty_folio(mapping, folio);
+ if (filemap_dirty_folio(mapping, folio)) {
f2fs_update_dirty_folio(inode, folio);
return true;
}
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index e06a0c478b39..3506ffcb31f8 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -2147,8 +2147,7 @@ static bool f2fs_dirty_node_folio(struct address_space *mapping,
if (IS_INODE(&folio->page))
f2fs_inode_chksum_set(F2FS_M_SB(mapping), &folio->page);
#endif
- if (!folio_test_dirty(folio)) {
- filemap_dirty_folio(mapping, folio);
+ if (filemap_dirty_folio(mapping, folio)) {
inc_page_count(F2FS_M_SB(mapping), F2FS_DIRTY_NODES);
set_page_private_reference(&folio->page);
return true;
--
2.35.1