Date:   Mon, 21 Nov 2016 15:27:23 +0100
From:   Jan Kara <jack@...e.cz>
To:     Nikolay Borisov <kernel@...p.com>
Cc:     Jan Kara <jack@...e.cz>, linux-ext4 <linux-ext4@...r.kernel.org>,
        Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>
Subject: Re: kernel BUG at fs/ext4/inode.c:2428!

On Mon 14-11-16 16:46:51, Nikolay Borisov wrote:
> 
> 
> On 11/14/2016 03:49 PM, Jan Kara wrote:
> > Hello,
> > 
> > On Mon 14-11-16 12:15:16, Nikolay Borisov wrote:
> >> So I hit the following BUG_ON on 3 separate servers: 
> >>
> >> [1387898.597939] sh (14886): drop_caches: 3
> >> [1387945.259613] ------------[ cut here ]------------
> >> [1387945.259791] kernel BUG at fs/ext4/inode.c:2428!
> >> [1387945.259964] invalid opcode: 0000 [#1] SMP 
> >> [1387945.263921] CPU: 9 PID: 8987 Comm: kworker/u24:23 Tainted: P           O    4.4.26-clouder1 #3
> >> [1387945.264213] Hardware name: Supermicro X9DRD-iF/LF/X9DRD-iF, BIOS 3.2 01/16/2015
> >> [1387945.264512] Workqueue: writeback wb_workfn (flush-253:8)
> >> [1387945.264780] task: ffff880287ca5280 ti: ffff8800064dc000 task.ti: ffff8800064dc000
> >> [1387945.265073] RIP: 0010:[<ffffffff8122a3ac>]  [<ffffffff8122a3ac>] mpage_prepare_extent_to_map+0x29c/0x2d0
> >> [1387945.265426] RSP: 0018:ffff8800064df960  EFLAGS: 00010246
> >> [1387945.265596] RAX: 02fffc0000030039 RBX: ffff8800064dfad0 RCX: 0000000000000537
> >> [1387945.265881] RDX: 000000000000231b RSI: 0000000000000000 RDI: ffffffff81a052a6
> >> [1387945.266165] RBP: ffff8800064dfa28 R08: 0000000000000000 R09: 0000000000000000
> >> [1387945.266450] R10: 0000000000000001 R11: 0000000000000100 R12: ffff8800064df980
> >> [1387945.266734] R13: 0000000000003400 R14: ffffffffffffffff R15: ffffea000686fbc0
> >> [1387945.267024] FS:  0000000000000000(0000) GS:ffff88047fd20000(0000) knlGS:0000000000000000
> >> [1387945.267315] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> [1387945.267487] CR2: ffffffffff600400 CR3: 00000004555ff000 CR4: 00000000000406e0
> >> [1387945.267765] Stack:
> >> [1387945.267925]  0000000000000000 ffff88015b3c2be0 ffff8800064df980 0000000000000538
> >> [1387945.268386]  0000000000000001 0000000000000000 ffffea000686fbc0 ffff88046bce1800
> >> [1387945.268850]  ffff8800064df9e8 ffffffff81274777 ffffffff02400040 0fd000086bce6800
> >> [1387945.269319] Call Trace:
> >> [1387945.269489]  [<ffffffff81274777>] ? jbd2__journal_start+0xe7/0x200
> >> [1387945.269663]  [<ffffffff8122e581>] ? ext4_writepages+0x3a1/0xcd0
> >> [1387945.269839]  [<ffffffff8125ba8d>] ? __ext4_journal_start_sb+0x6d/0x100
> >> [1387945.270013]  [<ffffffff8122e5b2>] ext4_writepages+0x3d2/0xcd0
> >> [1387945.270207]  [<ffffffffa07f878b>] ? leaf_space_used+0xcb/0x100 [btrfs]
> >> [1387945.270382]  [<ffffffff810823a1>] ? sched_clock_cpu+0xa1/0xb0
> >> [1387945.270556]  [<ffffffff8107beb4>] ? check_preempt_curr+0x54/0x90
> >> [1387945.270730]  [<ffffffff8107c07d>] ? ttwu_do_activate.constprop.92+0x5d/0x70
> >> [1387945.270905]  [<ffffffff8113735e>] do_writepages+0x1e/0x30
> >> [1387945.271076]  [<ffffffff811c6c85>] __writeback_single_inode+0x45/0x370
> >> [1387945.271250]  [<ffffffff811c74d2>] writeback_sb_inodes+0x252/0x570
> >> [1387945.271423]  [<ffffffff811c7879>] __writeback_inodes_wb+0x89/0xc0
> >> [1387945.271596]  [<ffffffff811c7bb8>] wb_writeback+0x268/0x300
> >> [1387945.271766]  [<ffffffff811c83e6>] wb_workfn+0x2d6/0x400
> >> [1387945.271938]  [<ffffffff81614ea8>] ? _raw_spin_lock_irqsave+0x18/0x50
> >> [1387945.272112]  [<ffffffff8106bf89>] process_one_work+0x159/0x450
> >> [1387945.272285]  [<ffffffff8106c639>] worker_thread+0x69/0x490
> >> [1387945.272456]  [<ffffffff8106c5d0>] ? rescuer_thread+0x350/0x350
> >> [1387945.272630]  [<ffffffff810717bf>] kthread+0xef/0x110
> >> [1387945.272803]  [<ffffffff810716d0>] ? kthread_park+0x60/0x60
> >> [1387945.272975]  [<ffffffff816156bf>] ret_from_fork+0x3f/0x70
> >> [1387945.273146]  [<ffffffff810716d0>] ? kthread_park+0x60/0x60
> >> [1387945.273322] Code: d2 e4 ff e8 67 6f 3e 00 48 8b 85 50 ff ff ff 49 39 c6 0f 83 15 fe ff ff 31 c0 eb a7 4c 89 ff e8 3b e8 ef ff e9 b8 fe ff ff 0f 0b <0f> 0b 48 8d bd 58 ff ff ff 89 85 48 ff ff ff e8 50 f8 f0 ff 8b 
> >> [1387945.276751] RIP  [<ffffffff8122a3ac>] mpage_prepare_extent_to_map+0x29c/0x2d0
> >> [1387945.277089]  RSP <ffff8800064df960>
> >>
> >> So a user triggers drop_caches and ext4 crashes due to it trying to 
> >> write a page that isn't fs-owned. ffffffff8122a3ac is : head = page_buffers(page);
> >> which has this: BUG_ON(!PagePrivate(page)); 
> >>
> >> page.flags is flags = 216168384067469369 (in binary: 0000001011111111111111000000000000000000000000110000000000111001) 
> >> so the 11th bit (PG_private) is not set, triggering the BUG_ON. The flags are 
> >> (PG_LOCKED|PG_UPTODATE|PG_DIRTY|MAPPEDTODISK|PG_RECLAIM). Do these flags seem 
> >> corrupt - uptodate and dirty being set at the same time? Maybe the page struct
> >> is being corrupted?
> >>
> >> page.private is actually NULL. The page does have an associated address_space 
> >> mapping. I've validated this since address_space.host is the same as the 
> >> inode member of the passed mpd. 
> > 
> > Interesting. I didn't see this yet. What mount options does the filesystem
> > use? The file where this happened is a regular file I assume, right? What
> > is blocksize and page size for the filesystem?
> 
> s_blocksize_bits = 12,
> s_blocksize = 4096,
> 
> And this is x86_64 so pagesize is also 4k. Unfortunately I cannot
> re-mount the file system since it has been converted to btrfs. However
> here are the options: rw,relatime,discard,stripe=32,data=ordered, these
> have been taken from an analogous mount. This is how it's supposed to
> have been created: mkfs.ext4 -b 4096 -K -E nodiscard,lazy_itable_init=1
> -O has_journal,large_file,resize_inode,sparse_super,uninit_bg
> 
> Since those values are from the system which supposedly created those,
> here are the raw values form the ext4_sb_info->s_mount_opt* members:
> s_mount_opt = 3892496400,
> s_mount_opt2 = 2,
> 
> And from ext4_super_block->s_feature_*:
> 
>   s_feature_compat = 0,
>   s_feature_incompat = 61267,
>   s_feature_ro_compat = 0,

This looks strange - COMPAT and RO_COMPAT features definitely should not be
zero (e.g. has_journal and sparse_super should be set), also INCOMPAT
features look weird - e.g. bit 0x800 is not used but it is set in incompat
features. Did you get the sb pointer right?

> > The page flags actually look rather consistent. The only thing that is
> 
> Why is UPTODATE and DIRTY set simultaneously. Don't they contradict each
> other?

They can be set simultaneously - 'uptodate' means page has at least as new
data as is on disk, 'dirty' means page has strictly newer data than on
disk.

What is page->index and how large is the inode (inode->i_size)?

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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