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Message-ID: <a364da58-f476-69fd-3f90-448f35c8e151@kernel.org>
Date: Sat, 20 Aug 2022 14:35:24 +0800
From: Chao Yu <chao@...nel.org>
To: Shuqi Zhang <zhangshuqi3@...wei.com>, jaegeuk@...nel.org
Cc: linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] f2fs: fix wrong dirty page count when race between
mmap and fallocate.
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 <zhangshuqi3@...wei.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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