Messages in this thread Patch in this message | | | Date | Sat, 20 Aug 2022 15:19:43 -0700 | From | Jaegeuk Kim <> | Subject | Re: [f2fs-dev] [PATCH -next] f2fs: fix wrong dirty page count when race between mmap and fallocate. |
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On 08/20, Jaegeuk Kim wrote: > On 08/20, Chao Yu wrote: > > 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()? > > Found this. > > 2637 * The caller must ensure this doesn't race with truncation. Most will > 2638 * simply hold the folio lock, but e.g. zap_pte_range() calls with the > 2639 * folio mapped and the pte lock held, which also locks out truncation. > 2640 */ > 2641 bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio) > 2642 { > > > > > 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);
Actually we don't need to call SetPageUptodate() since set_page_dirty() should do? And, it seems the call stack is out-dated as well.
By the way, do we just need to get the right count by this?
--- 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; } > > > + f2fs_update_time(sbi, REQ_TIME); > > > out_sem: > > > filemap_invalidate_unlock_shared(inode->i_mapping); > > > _______________________________________________ > Linux-f2fs-devel mailing list > Linux-f2fs-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
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