Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758801AbaKUPtx (ORCPT ); Fri, 21 Nov 2014 10:49:53 -0500 Received: from mx1.redhat.com ([209.132.183.28]:56489 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758698AbaKUPtw (ORCPT ); Fri, 21 Nov 2014 10:49:52 -0500 Date: Fri, 21 Nov 2014 10:49:21 -0500 From: Mike Snitzer To: Christoph Hellwig Cc: axboe@kernel.dk, martin.petersen@oracle.com, mst@redhat.com, rusty@rustcorp.com.au, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, dm-devel@redhat.com, Paolo Bonzini Subject: Re: virtio_blk: fix defaults for max_hw_sectors and max_segment_size Message-ID: <20141121154920.GA7644@redhat.com> References: <20141120190058.GA31214@redhat.com> <20141121095456.GB8866@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141121095456.GB8866@infradead.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 21 2014 at 4:54am -0500, Christoph Hellwig wrote: > On Thu, Nov 20, 2014 at 02:00:59PM -0500, Mike Snitzer wrote: > > virtio_blk incorrectly established -1U as the default for these > > queue_limits. Set these limits to sane default values to avoid crashing > > the kernel. But the virtio-blk protocol should probably be extended to > > allow proper stacking of the disk's limits from the host. > > > > This change fixes a crash that was reported when virtio-blk was used to > > test linux-dm.git commit 604ea90641b4 ("dm thin: adjust max_sectors_kb > > based on thinp blocksize") that will initially set max_sectors to > > max_hw_sectors and then rounddown to the first power-of-2 factor of the > > DM thin-pool's blocksize. Basically that commit assumes drivers don't > > suck when establishing max_hw_sectors so it acted like a canary in the > > coal mine. > > Is that a crash in the host or guest? What kind of mishandling did you > see? Unless the recent virtio standard changed anything the host > should be able to handle our arbitrary limits, and even if it doesn't > that something we need to hash out with qemu and the virtio standards > folks. Some good news: this guest crash isn't an issue with recent kernels (so upstream, fedora 20, RHEL7, etc aren't impacted -- Jens feel free to drop my virtio_blk patch; even though some of it's limits are clearly broken I'll defer to the virtio_blk developers on the best way forward -- sorry for the noise!). The BUG I saw only seems to impact RHEL6 kernels so far (note to self, actually _test_ on upstream before reporting a crash against upstream!) [root@RHEL-6 ~]# echo 1073741824 > /sys/block/vdc/queue/max_sectors_kb [root@RHEL-6 ~]# lvs Message from syslogd@RHEL-6 at Nov 21 15:32:15 ... kernel:Kernel panic - not syncing: Fatal exception Here is the RHEL6 guest crash, just for full disclosure: kernel BUG at fs/direct-io.c:696! invalid opcode: 0000 [#1] SMP last sysfs file: /sys/devices/virtual/block/dm-4/dev CPU 0 Modules linked in: nfs lockd fscache auth_rpcgss nfs_acl sunrpc ipv6 ext2 dm_thin_pool dm_bio_prison dm_persistent_data dm_bufio libcrc32c dm_mirror dm_region_hash dm_log dm_mod microcode virtio_balloon i2c_piix4 i2c_core virtio_net ext4 jbd2 mbcache virtio_blk virtio_pci virtio_ring virtio pata_acpi ata_generic ata_piix [last unloaded: speedstep_lib] Pid: 1679, comm: lvs Not tainted 2.6.32 #6 Bochs Bochs RIP: 0010:[] [] __blockdev_direct_IO_newtrunc+0x986/0x1270 RSP: 0018:ffff88011a11ba48 EFLAGS: 00010287 RAX: 0000000000000000 RBX: ffff8801192fbd28 RCX: 0000000000001000 RDX: ffffea0003b3d218 RSI: ffff88011aac4300 RDI: ffff880118572378 RBP: ffff88011a11bbe8 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801192fbd00 R13: 0000000000000000 R14: ffff880118c3cac0 R15: 0000000000000000 FS: 00007fde78bc37a0(0000) GS:ffff880028200000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000012706f0 CR3: 000000011a432000 CR4: 00000000000407f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Process lvs (pid: 1679, threadinfo ffff88011a11a000, task ffff8801185a4aa0) Stack: ffff88011a11bb48 ffff88011a11baa8 ffff88010000000c ffff88011a11bb18 0000000000000000 0000000000000000 ffff88011a11bdc8 ffff88011a11beb8 0000000c1a11baa8 ffff880118c3cb98 0000000000000000 0000000018c3ccb8 Call Trace: [] ? blkdev_get_block+0x0/0x20 [] __blockdev_direct_IO+0x77/0xe0 [] ? blkdev_get_block+0x0/0x20 [] blkdev_direct_IO+0x57/0x60 [] ? blkdev_get_block+0x0/0x20 [] generic_file_aio_read+0x6bb/0x700 [] ? blkdev_get+0x10/0x20 [] ? blkdev_open+0x0/0xc0 [] ? __dentry_open+0x23f/0x360 [] blkdev_aio_read+0x51/0x80 [] do_sync_read+0xfa/0x140 [] ? autoremove_wake_function+0x0/0x40 [] ? block_ioctl+0x3c/0x40 [] ? vfs_ioctl+0x22/0xa0 [] ? do_vfs_ioctl+0x84/0x580 [] ? security_file_permission+0x16/0x20 [] vfs_read+0xb5/0x1a0 [] sys_read+0x51/0x90 [] ? __audit_syscall_exit+0x25e/0x290 [] system_call_fastpath+0x16/0x1b Code: fe ff ff c7 85 fc fe ff ff 00 00 00 00 48 89 95 10 ff ff ff 8b 95 34 ff ff ff e8 46 ac ff ff 3b 85 34 ff ff ff 0f 84 fc 02 00 00 <0f> 0b eb fe 8b 9d 34 ff ff ff 8b 85 30 ff ff ff 01 d8 85 c0 0f RIP [] __blockdev_direct_IO_newtrunc+0x986/0x1270 RSP ---[ end trace 73be5dcaf8939399 ]--- Kernel panic - not syncing: Fatal exception -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/