Messages in this thread | | | Date | Sat, 20 Aug 2022 14:35:24 +0800 | Subject | Re: [PATCH -next] f2fs: fix wrong dirty page count when race between mmap and fallocate. | From | Chao Yu <> |
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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@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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