From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A723249BD80 for ; Thu, 10 Sep 2026 14:12:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789049546; cv=none; b=ZVQu6wrMYK46vmrA15pydDo82ETCztYjRM7sQuuQfLdNE3uuRzJ/MHQf1dYfZ9VxXJKB1ZlBUTnVng0kpexCKOeHY+02l/s5VAkPRUer1OAbPDGT6UPA/3tjC3jJ6Y/Wkl+VRio+vxYHGQBIp6P7FCpGFZaPcwmUidVOR2KQrd0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789049546; c=relaxed/simple; bh=0Mhh4OUnCgSLgw0dCoDJwchdD8Dvz9j909zdSSyHCeg=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=ZVVMsz747gYuekLTsWwaM8GSQWOddB6Zd9zTmWRuLsOr4d9CgE/0vJr9kTLg1FP9uEgfcOujPpJnqLbl/MII5z4/VymGPE4HpO3G9fxxO0EHgZZYAvm4vmYyW9Bps1q/aay34aciyVY8q2thAnqaCXn16LnM1AIKYIzfj7aLUQc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DR6cm8ko; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="DR6cm8ko" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EDE4A1F000FF; Thu, 10 Sep 2026 14:12:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789049545; bh=yktsf0ORBBGvD3SUCnSD4sWyXidehM6lXLw0baTYOAM=; h=Date:Cc:Subject:To:References:From:In-Reply-To; b=DR6cm8ko/3qgt7iRmoOIc+GkqzbQjdop9yWq5Qik1mdngrStdgw91yb2SUbPXRgbW +BwGaOl0FycosQqQyaUBgDbkqExHUPG+pOv2sSls+AsxWJg54mEnXl52PjWuCrreGi hwCwDtwMH8OgDzuEjzEznCDdswRjeUj5abQ7ggKoPngUWt3BtZBfFdRcsxW0QRDuz7 n2TOMEkhjmrSdH8t1oY+Y4w6VHgCKAwBLDvc/SfIxmb3hLjbdI3UPxIzNjk6rWWrSW u7T00RS1twz/70OYQ+4j4WksFSYOKY/C9f7gbGrGpx6iSrBeiVtAzffqbAPx7Ny/Q2 acKYLC0X1B4nQ== Message-ID: <8b3df80c-2cf6-4331-89ac-4ae75edf5b40@kernel.org> Date: Thu, 10 Sep 2026 22:12:22 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: chao@kernel.org, jaegeuk@kernel.org, stable@kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Subject: Re: [f2fs-dev] [PATCH] f2fs: compress: fix to handle race between truncate and writeback To: Zhiguo Niu References: <20260910022258.3308187-1-chao@kernel.org> Content-Language: en-US From: Chao Yu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 9/10/26 15:22, Zhiguo Niu wrote: > Chao Yu via Linux-f2fs-devel > 于2026年9月10日周四 10:24写道： >> >> From: Chao Yu >> >> fsstress reports a kernel BUG in f2fs_truncate_partial_cluster(): >> >> kernel BUG at fs/f2fs/compress.c:1238! >> RIP: 0010:f2fs_truncate_partial_cluster+0x292/0x2a0 >> Call Trace: >> >> f2fs_truncate+0xf6/0x210 >> f2fs_setattr+0x6b7/0x770 >> notify_change+0x33b/0x520 >> do_truncate+0xc2/0xf0 >> vfs_truncate+0x153/0x1d0 >> ksys_truncate+0x78/0xd0 >> __x64_sys_truncate+0x16/0x20 >> do_syscall_64+0xbe/0x540 >> >> The root cause is that Thread A (truncate) and Thread B (background >> writeback or fsync) can race as follows: >> >> Thread A Thread B >> - f2fs_setattr >> - f2fs_truncate >> - f2fs_truncate_blocks >> - f2fs_truncate_partial_cluster >> - f2fs_is_compressed_cluster >> return 1 >> - f2fs_write_cache_pages >> - f2fs_write_multi_pages >> - f2fs_write_raw_pages >> - f2fs_write_single_data_page >> dn.data_blkaddr != COMPRESS_ADDR >> (cluster converted to normal) >> - f2fs_prepare_compress_overwrite >> - f2fs_is_compressed_cluster >> return 0 >> - return 0 >> - f2fs_bug_on(sbi, err == 0): BUG! >> >> Writeback path does not acquire i_gc_rwsem or filemap_invalidate_lock. >> When a compressed cluster fails compression during writeback, it is >> overwritten with raw data blocks. If Thread A checked >> f2fs_is_compressed_cluster() before the conversion, but calls >> f2fs_prepare_compress_overwrite() after the conversion, >> f2fs_prepare_compress_overwrite() returns 0 because the cluster is no >> longer a compressed cluster. >> >> To fix this, remove the f2fs_bug_on() and retry checking the cluster status >> when f2fs_prepare_compress_overwrite() returns 0, so that it can fall back >> to f2fs_do_truncate_blocks() to handle it as a normal cluster. >> >> Cc: stable@kernel.org >> Fixes: 3265d3db1f16 ("f2fs: support partial truncation on compressed inode") >> Signed-off-by: Chao Yu >> --- >> fs/f2fs/compress.c | 8 ++++---- >> 1 file changed, 4 insertions(+), 4 deletions(-) >> >> diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c >> index ce88092d9ce2..e1cc7185428e 100644 >> --- a/fs/f2fs/compress.c >> +++ b/fs/f2fs/compress.c >> @@ -1222,6 +1222,7 @@ int f2fs_truncate_partial_cluster(struct inode *inode, u64 from, bool lock) >> int i; >> int err; >> >> +repeat: >> err = f2fs_is_compressed_cluster(inode, start_idx); >> if (err < 0) >> return err; >> @@ -1233,11 +1234,10 @@ int f2fs_truncate_partial_cluster(struct inode *inode, u64 from, bool lock) >> /* truncate compressed cluster */ >> err = f2fs_prepare_compress_overwrite(inode, &pagep, >> start_idx, &fsdata); >> + if (err == 0) >> + goto repeat; > Hi Chao, > some comments here will be easier to understand？ Zhiguo, add comments in v2, thanks for the review. Thanks, > other LGTM > Reviewed-by: Zhiguo Niu > thanks! >> >> - /* should not be a normal cluster */ >> - f2fs_bug_on(F2FS_I_SB(inode), err == 0); >> - >> - if (err <= 0) >> + if (err < 0) >> return err; >> >> rpages = fsdata; >> -- >> 2.49.0 >> >> >> >> _______________________________________________ >> Linux-f2fs-devel mailing list >> Linux-f2fs-devel@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel