On 2022/8/15 16:15, Shuqi Zhang wrote:
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(i_mmap_sem)
lock_page
if (PageMappedToDisk(page))
goto out;
// set_page_dirty --NOT RUN
out: up_read(i_mmap_sem)
lock_page
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
f2fs_set_data_page_dirty
I didn't get it, why zap_pte_range() can set page dirty w/o lock_page?
I found it's very easy to reproduce this bug, but previously I never saw this...
is there any code udpate around truncate_pagecache()?
Thanks,
if (!PageDirty(page)) {
fault_dirty_shared_page
f2fs_set_data_page_dirty
if (!PageDirty(page)) {
__set_page_dirty_nobuffer
f2fs_update_dirty_page // ++
}
unlock_page
__set_page_dirty_nobuffers
f2fs_update_dirty_page // 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_set_data_page_dirty function. Page is set to dirty only ONCE,
but the count is added TWICE by calling f2fs_update_dirty_page.
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.
If making sure f2fs_vm_page_mkwrite calls set_page_dirty within immap
lock area, page will already be dirtied when running into
fault_dirty_shared_page-f2fs_set_data_page_dirty.
The count of dirty page will not be increased wrong times.
Signed-off-by: Shuqi Zhang <zhangshu...@huawei.com>
---
fs/f2fs/file.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index ce4905a073b3..d837359a9c00 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -140,7 +140,7 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
* check to see if the page is mapped already (no holes)
*/
if (PageMappedToDisk(page))
- goto out_sem;
+ goto set_dirty;
/* page is wholly or partially inside EOF */
if (((loff_t)(page->index + 1) << PAGE_SHIFT) >
@@ -150,14 +150,15 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault
*vmf)
offset = i_size_read(inode) & ~PAGE_MASK;
zero_user_segment(page, offset, PAGE_SIZE);
}
- set_page_dirty(page);
- if (!PageUptodate(page))
- SetPageUptodate(page);
f2fs_update_iostat(sbi, APP_MAPPED_IO, F2FS_BLKSIZE);
- f2fs_update_time(sbi, REQ_TIME);
+set_dirty:
trace_f2fs_vm_page_mkwrite(page, DATA);
+ set_page_dirty(page);
+ if (!PageUptodate(page))
+ SetPageUptodate(page);
+ f2fs_update_time(sbi, REQ_TIME);
out_sem:
filemap_invalidate_unlock_shared(inode->i_mapping);
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