Hello, We're using qemu's guest agent daemon, qemu-ga, to freeze ext4 filesystems in guest virtual machines before taking an LVM snapshot of the disk volume in the host. However, in the guests' dmesg, we're consistently seeing warnings like: [1246478.632936] WARNING: at /build/buildd/linux-lts-raring-3.8.0/fs/ext4/super.c:339 ext4_journal_start_sb+0x159/0x160() Looking at the source at https://github.com/torvalds/linux/blob/v3.8/fs/ext4/super.c#L339, this warning seems to be generated if the function is reached despite the filesystem being marked as frozen: WARN_ON(sb->s_writers.frozen == SB_FREEZE_COMPLETE); In 3.12, this has been moved to https://github.com/torvalds/linux/blob/v3.12/fs/ext4/ext4_jbd2.c#L48. Is this something we should be concerned about? The process that seems to be responsible for triggering it is mysqld, so we're concerned the databases in our snapshots have a higher possibility of being corrupt. (Taking online snapshots of databases like this is always risky, of course, but this just makes us a little more nervous :) ) Full kernel warning is attached below. Thank you! [1246478.632930] ------------[ cut here ]------------ [1246478.632936] WARNING: at /build/buildd/linux-lts-raring-3.8.0/fs/ext4/super.c:339 ext4_journal_start_sb+0x159/0x160() [1246478.632938] Hardware name: Bochs [1246478.632939] Modules linked in: cirrus(F) ttm(F) drm_kms_helper(F) drm(F) sysimgblt(F) psmouse(F) sysfillrect(F) serio_raw(F) syscopyarea(F) microcode(F) virtio_console(F) lp(F) virtio_balloon(F) mac_hid(F) i2c_piix4(F) ext2(F) parport(F) floppy(F) e1000(F) [1246478.632973] Pid: 2856, comm: mysqld Tainted: GF W 3.8.0-33-generic #48~precise1-Ubuntu [1246478.632975] Call Trace: [1246478.632981] [<ffffffff81059b6f>] warn_slowpath_common+0x7f/0xc0 [1246478.632985] [<ffffffff81059bca>] warn_slowpath_null+0x1a/0x20 [1246478.632989] [<ffffffff8125eb59>] ext4_journal_start_sb+0x159/0x160 [1246478.632993] [<ffffffff8123f1c8>] ? _ext4_get_block+0x138/0x170 [1246478.632997] [<ffffffff8123f1c8>] _ext4_get_block+0x138/0x170 [1246478.633002] [<ffffffff8104e070>] ? get_user_pages_fast+0xe0/0x1a0 [1246478.633006] [<ffffffff8123f263>] ext4_get_block_write+0x13/0x20 [1246478.633009] [<ffffffff811d6d3a>] get_more_blocks+0x6a/0xa0 [1246478.633013] [<ffffffff811d7a7e>] do_direct_IO+0x4be/0x1530 [1246478.633018] [<ffffffff8107f9ab>] ? bit_waitqueue+0x1b/0xc0 [1246478.633022] [<ffffffff81186221>] ? kmem_cache_alloc+0x31/0x140 [1246478.633026] [<ffffffff811d8f22>] do_blockdev_direct_IO+0x432/0x13e0 [1246478.633030] [<ffffffff8123f250>] ? noalloc_get_block_write+0x30/0x30 [1246478.633035] [<ffffffff811d9f25>] __blockdev_direct_IO+0x55/0x60 [1246478.633039] [<ffffffff8123f250>] ? noalloc_get_block_write+0x30/0x30 [1246478.633042] [<ffffffff8123ab30>] ? ext4_journalled_invalidatepage+0x30/0x30 [1246478.633046] [<ffffffff8123bcd0>] ext4_ext_direct_IO+0x130/0x250 [1246478.633050] [<ffffffff8123f250>] ? noalloc_get_block_write+0x30/0x30 [1246478.633053] [<ffffffff8123ab30>] ? ext4_journalled_invalidatepage+0x30/0x30 [1246478.633057] [<ffffffff8123c1ad>] ext4_direct_IO+0x1ad/0x230 [1246478.633061] [<ffffffff8108e3ca>] ? finish_task_switch+0x4a/0xf0 [1246478.633065] [<ffffffff811368d6>] generic_file_direct_write+0xc6/0x180 [1246478.633068] [<ffffffff81136c6d>] __generic_file_aio_write+0x2dd/0x3b0 [1246478.633072] [<ffffffff816e5848>] ext4_file_dio_write+0x243/0x320 [1246478.633076] [<ffffffff810b81b2>] ? unqueue_me+0x52/0x80 [1246478.633079] [<ffffffff81236ed8>] ext4_file_write+0xc8/0xe0 [1246478.633084] [<ffffffff8119b333>] do_sync_write+0xa3/0xe0 [1246478.633089] [<ffffffff8119b9d3>] vfs_write+0xb3/0x180 [1246478.633093] [<ffffffff8119be9a>] sys_pwrite64+0x9a/0xa0 [1246478.633097] [<ffffffff816fd15d>] system_call_fastpath+0x1a/0x1f [1246478.633099] ---[ end trace f37019187d44de90 ]--- Please Note: Rapita Systems has a new address and telephone number. Telephone: +44 1904 413945 Address: Rapita Systems Ltd, Atlas House, Osbaldwick Link Road, YORK, YO10 3JB United Kingdom -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
