The patch below does not apply to the 6.12-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y git checkout FETCH_HEAD git cherry-pick -x 10b591e7fb7cdc8c1e53e9c000dc0ef7069aaa76 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025122921-captivate-substance-994f@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 10b591e7fb7cdc8c1e53e9c000dc0ef7069aaa76 Mon Sep 17 00:00:00 2001 From: Chao Yu chao@kernel.org Date: Wed, 22 Oct 2025 11:06:36 +0800 Subject: [PATCH] f2fs: fix to avoid updating compression context during writeback
Bai, Shuangpeng sjb7183@psu.edu reported a bug as below:
Oops: divide error: 0000 [#1] SMP KASAN PTI CPU: 0 UID: 0 PID: 11441 Comm: syz.0.46 Not tainted 6.17.0 #1 PREEMPT(full) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:f2fs_all_cluster_page_ready+0x106/0x550 fs/f2fs/compress.c:857 Call Trace: <TASK> f2fs_write_cache_pages fs/f2fs/data.c:3078 [inline] __f2fs_write_data_pages fs/f2fs/data.c:3290 [inline] f2fs_write_data_pages+0x1c19/0x3600 fs/f2fs/data.c:3317 do_writepages+0x38e/0x640 mm/page-writeback.c:2634 filemap_fdatawrite_wbc mm/filemap.c:386 [inline] __filemap_fdatawrite_range mm/filemap.c:419 [inline] file_write_and_wait_range+0x2ba/0x3e0 mm/filemap.c:794 f2fs_do_sync_file+0x6e6/0x1b00 fs/f2fs/file.c:294 generic_write_sync include/linux/fs.h:3043 [inline] f2fs_file_write_iter+0x76e/0x2700 fs/f2fs/file.c:5259 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x7e9/0xe00 fs/read_write.c:686 ksys_write+0x19d/0x2d0 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xf7/0x470 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f
The bug was triggered w/ below race condition:
fsync setattr ioctl - f2fs_do_sync_file - file_write_and_wait_range - f2fs_write_cache_pages : inode is non-compressed : cc.cluster_size = F2FS_I(inode)->i_cluster_size = 0 - tag_pages_for_writeback - f2fs_setattr - truncate_setsize - f2fs_truncate - f2fs_fileattr_set - f2fs_setflags_common - set_compress_context : F2FS_I(inode)->i_cluster_size = 4 : set_inode_flag(inode, FI_COMPRESSED_FILE) - f2fs_compressed_file : return true - f2fs_all_cluster_page_ready : "pgidx % cc->cluster_size" trigger dividing 0 issue
Let's change as below to fix this issue: - introduce a new atomic type variable .writeback in structure f2fs_inode_info to track the number of threads which calling f2fs_write_cache_pages(). - use .i_sem lock to protect .writeback update. - check .writeback before update compression context in f2fs_setflags_common() to avoid race w/ ->writepages.
Fixes: 4c8ff7095bef ("f2fs: support data compression") Cc: stable@kernel.org Reported-by: Bai, Shuangpeng sjb7183@psu.edu Tested-by: Bai, Shuangpeng sjb7183@psu.edu Closes: https://lore.kernel.org/lkml/44D8F7B3-68AD-425F-9915-65D27591F93F@psu.edu Signed-off-by: Chao Yu chao@kernel.org Signed-off-by: Jaegeuk Kim jaegeuk@kernel.org
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c index eec691262fec..b92d362a02d6 100644 --- a/fs/f2fs/data.c +++ b/fs/f2fs/data.c @@ -3222,6 +3222,19 @@ static inline bool __should_serialize_io(struct inode *inode, return false; }
+static inline void account_writeback(struct inode *inode, bool inc) +{ + if (!f2fs_sb_has_compression(F2FS_I_SB(inode))) + return; + + f2fs_down_read(&F2FS_I(inode)->i_sem); + if (inc) + atomic_inc(&F2FS_I(inode)->writeback); + else + atomic_dec(&F2FS_I(inode)->writeback); + f2fs_up_read(&F2FS_I(inode)->i_sem); +} + static int __f2fs_write_data_pages(struct address_space *mapping, struct writeback_control *wbc, enum iostat_type io_type) @@ -3267,10 +3280,14 @@ static int __f2fs_write_data_pages(struct address_space *mapping, locked = true; }
+ account_writeback(inode, true); + blk_start_plug(&plug); ret = f2fs_write_cache_pages(mapping, wbc, io_type); blk_finish_plug(&plug);
+ account_writeback(inode, false); + if (locked) mutex_unlock(&sbi->writepages);
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h index 575f9666c3b7..e69b01c1173a 100644 --- a/fs/f2fs/f2fs.h +++ b/fs/f2fs/f2fs.h @@ -947,6 +947,7 @@ struct f2fs_inode_info { unsigned char i_compress_level; /* compress level (lz4hc,zstd) */ unsigned char i_compress_flag; /* compress flag */ unsigned int i_cluster_size; /* cluster size */ + atomic_t writeback; /* count # of writeback thread */
unsigned int atomic_write_cnt; loff_t original_i_size; /* original i_size before atomic write */ @@ -4663,7 +4664,7 @@ static inline bool f2fs_disable_compressed_file(struct inode *inode) f2fs_up_write(&fi->i_sem); return true; } - if (f2fs_is_mmap_file(inode) || + if (f2fs_is_mmap_file(inode) || atomic_read(&fi->writeback) || (S_ISREG(inode->i_mode) && F2FS_HAS_BLOCKS(inode))) { f2fs_up_write(&fi->i_sem); return false; diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c index c045e38e60ee..6d42e2d28861 100644 --- a/fs/f2fs/file.c +++ b/fs/f2fs/file.c @@ -2128,8 +2128,9 @@ static int f2fs_setflags_common(struct inode *inode, u32 iflags, u32 mask)
f2fs_down_write(&fi->i_sem); if (!f2fs_may_compress(inode) || - (S_ISREG(inode->i_mode) && - F2FS_HAS_BLOCKS(inode))) { + atomic_read(&fi->writeback) || + (S_ISREG(inode->i_mode) && + F2FS_HAS_BLOCKS(inode))) { f2fs_up_write(&fi->i_sem); return -EINVAL; } diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c index cb65ca90f9f6..d0b5791a1f8c 100644 --- a/fs/f2fs/super.c +++ b/fs/f2fs/super.c @@ -1759,6 +1759,7 @@ static struct inode *f2fs_alloc_inode(struct super_block *sb) atomic_set(&fi->dirty_pages, 0); atomic_set(&fi->i_compr_blocks, 0); atomic_set(&fi->open_count, 0); + atomic_set(&fi->writeback, 0); init_f2fs_rwsem(&fi->i_sem); spin_lock_init(&fi->i_size_lock); INIT_LIST_HEAD(&fi->dirty_list);