From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0F67CC4363A for ; Wed, 21 Oct 2020 19:03:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9A4412177B for ; Wed, 21 Oct 2020 19:03:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2504617AbgJUTDx (ORCPT ); Wed, 21 Oct 2020 15:03:53 -0400 Received: from mx2.suse.de ([195.135.220.15]:60140 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2502390AbgJUTDw (ORCPT ); Wed, 21 Oct 2020 15:03:52 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E9E70AE95; Wed, 21 Oct 2020 19:03:50 +0000 (UTC) Date: Wed, 21 Oct 2020 14:03:48 -0500 From: Goldwyn Rodrigues To: Johannes Thumshirn Cc: David Sterba , linux-btrfs@vger.kernel.org, Matthew Wilcox Subject: Re: [PATCH] btrfs: skip call to generic_file_buffered_read if we don't need to Message-ID: <20201021190348.vqc6jtmppel63ltc@fiona> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 2:22 22/10, Johannes Thumshirn wrote: > Since we switched to the iomap infrastructure in b5ff9f1a96e8f ("btrfs: > switch to iomap for direct IO") we're calling generic_file_buffered_read() > directly and not via generic_file_read_iter() anymore. > > If the read could read everything there is no need to bother calling > generic_file_buffered_read(), like it is handled in > generic_file_read_iter(). > > If we call generic_file_buffered_read() in this case we can hit a > situation where we do an invalid readahead and cause this UBSAN splat: > johannes@redsun60:linux(btrfs-misc-next)$ kasan_symbolize.py < ubsan.txt > rapido1:/home/johannes/src/xfstests-dev# cat results/generic/091.dmesg > run fstests generic/091 at 2020-10-21 10:52:32 > ================================================================================ > UBSAN: shift-out-of-bounds in ./include/linux/log2.h:57:13 > shift exponent 64 is too large for 64-bit type 'long unsigned int' > CPU: 0 PID: 656 Comm: fsx Not tainted 5.9.0-rc7+ #821 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4-rebuilt.opensuse.org 04/01/2014 > Call Trace: > __dump_stack lib/dump_stack.c:77 > dump_stack+0x57/0x70 lib/dump_stack.c:118 > ubsan_epilogue+0x5/0x40 lib/ubsan.c:148 > __ubsan_handle_shift_out_of_bounds.cold+0x61/0xe9 lib/ubsan.c:395 > __roundup_pow_of_two ./include/linux/log2.h:57 > get_init_ra_size mm/readahead.c:318 > ondemand_readahead.cold+0x16/0x2c mm/readahead.c:530 > generic_file_buffered_read+0x3ac/0x840 mm/filemap.c:2199 > call_read_iter ./include/linux/fs.h:1876 > new_sync_read+0x102/0x180 fs/read_write.c:415 > vfs_read+0x11c/0x1a0 fs/read_write.c:481 > ksys_read+0x4f/0xc0 fs/read_write.c:615 > do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 arch/x86/entry/entry_64.S:118 > RIP: 0033:0x7fe87fee992e > Code: 0f 1f 40 00 48 8b 15 a1 96 00 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb ba 0f 1f 00 64 8b 04 25 18 00 00 00 85 c0 75 14 0f 05 <48> 3d 00 f0 ff ff 77 5a c3 66 0f 1f 84 00 00 00 00 00 48 83 ec 28 > RSP: 002b:00007ffe01605278 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 > RAX: ffffffffffffffda RBX: 000000000004f000 RCX: 00007fe87fee992e > RDX: 0000000000004000 RSI: 0000000001677000 RDI: 0000000000000003 > RBP: 000000000004f000 R08: 0000000000004000 R09: 000000000004f000 > R10: 0000000000053000 R11: 0000000000000246 R12: 0000000000004000 > R13: 0000000000000000 R14: 000000000007a120 R15: 0000000000000000 > ================================================================================ > BTRFS info (device nullb0): has skinny extents > BTRFS info (device nullb0): ZONED mode enabled, zone size 268435456 B > BTRFS info (device nullb0): enabling ssd optimizations > > Fixes: b5ff9f1a96e8f ("btrfs: switch to iomap for direct IO") > Signed-off-by: Johannes Thumshirn > --- > fs/btrfs/file.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c > index 6f5ecba74f54..8e6def2c463d 100644 > --- a/fs/btrfs/file.c > +++ b/fs/btrfs/file.c > @@ -3612,7 +3612,7 @@ static ssize_t btrfs_file_read_iter(struct kiocb *iocb, struct iov_iter *to) > inode_lock_shared(inode); > ret = btrfs_direct_IO(iocb, to); > inode_unlock_shared(inode); > - if (ret < 0) > + if (ret < 0 || (ret > 0 && iov_iter_count(to) == 0)) > return ret; > } > You can also include the check (iocb->ki_pos >= i_size_read(file_inode(iocb->ki_filp)) -- Goldwyn