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 3D8BF48EC87 for ; Thu, 10 Sep 2026 14:11:33 +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=1789049494; cv=none; b=DFKZX9nCQu+39yvafMGHG5y4TScdXBQ7OmCJnTgofTC2rofWtmRhco91BtEV76zUmaaP1r1vzVuaYUSCt1zv19d7raRaKJMENShaZ1H87x5Aam+yY5AN1Q/76ls/fHKkMNVukxEpeXKdi7t1ea4urKjHCCctelO3lEjEK+ABCtg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789049494; c=relaxed/simple; bh=Jm6epicdz0HSV7XcEy9qi54XWYlDNHoU6JavwblrO2E=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=XMGcdFq/LTx6ubS+xxXg3tRFSUYRxQkuJAn6SsIN3MXsFLKGN4KL/Yg8p3i2Ayz+3ESYxEt2yfDHfVIscf9WuJy638Qiu5lIOgb+859fo07hYixzBdct1x+NSh65BxkxU0zx4NTUjqxgSFCH/AA5Bmsc9KHneOe7Jl+mMuICTcE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FQsyExdw; 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="FQsyExdw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 932041F000FF; Thu, 10 Sep 2026 14:11:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789049492; bh=lLAqtjys13v8tLrbWLlIUVt/Fd351A9zIJ5wib7pFzk=; h=From:To:Cc:Subject:Date; b=FQsyExdwj3+gfD/vJkurNxCcccf6ZwHpcfxTLN7KvYLmoL/SaFvLZAwDdIOMe2AQ7 9EN0Ahc9ZsjmvSf4ZTcqWRkA8laqj7mPz1fDMDKfi90+STB2T4dRrYwrU3BVwWarDC 5G/Bbmwmr7REdRhhQIEgASmhqv4LxW8p1Op3S+ypqhUBJmkN5NKjyFNhQUbwrv1RUn J687HNkvyuOpuYyRbWYaHx8SGdvQZk50GShHer1np1FMrdKLlr+lNaRJTCxOqm6PHt RdDFDYv/tZ4OA2lXUDwFPHxJym3Za1cBm0TUtFE2pYJJ4Aa5YCeeuIOwjVBEFStns8 /xivgPQA4U6Sg== From: Chao Yu To: jaegeuk@kernel.org Cc: linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, Chao Yu , stable@kernel.org, Zhiguo Niu Subject: [PATCH v2] f2fs: compress: fix to handle race between truncate and writeback Date: Thu, 10 Sep 2026 22:11:26 +0800 Message-ID: <20260910141126.1309794-1-chao@kernel.org> X-Mailer: git-send-email 2.55.0.1003.g10538fe699-goog Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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") Reviewed-by: Zhiguo Niu Signed-off-by: Chao Yu --- fs/f2fs/compress.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c index ce88092d9ce2..b71107604012 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; @@ -1233,12 +1234,11 @@ 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); - - /* should not be a normal cluster */ - f2fs_bug_on(F2FS_I_SB(inode), err == 0); - - if (err <= 0) + if (err < 0) return err; + else if (err == 0) + /* the cluster became non-compressed one due to race case */ + goto repeat; rpages = fsdata; -- 2.49.0