Re: ext4 regression panic

[Jan Kara <jack@suse.cz>]

Hi Murphy!

On Thu 21-01-21 18:15:47, Murphy Zhou wrote:
> A panic was introduced by this commit. It's easy and reliable to
> reproduce.

Thanks for report! The problem seems to be that ext4_mb_init() is called
only after we call ext4_iget() to fetch the root inode. So if ext4_iget()
finds fs corruption and reports an error, we journal it but on commit we
find sbi->s_freed_data_list uninitialized and crash. I actually don't think
there's a reason for ext4_mb_init() to happen that late. I'll send a fix...

								Honza

> 
> commit 2d01ddc86606564fb08c56e3bc93a0693895f710
> Author: Jan Kara <jack@suse.cz>
> Date:   Wed Dec 16 11:18:40 2020 +0100
> 
>     ext4: save error info to sb through journal if available
> 
> 
> --- Call trace ------------
> 
> [44.391771] EXT4-fs error (device loop0): ext4_fill_super:4943: inode #2: comm mount: iget: root inode unallocated
> [44.401842] BUG: kernel NULL pointer dereference, address: 0000000000000034
> [44.406155] #PF: supervisor read access in kernel mode
> [44.409317] #PF: error_code(0x0000) - not-present page
> [44.412482] PGD 0 P4D 0
> [44.414085] Oops: 0000 [#1] SMP PTI
> [44.416256] CPU: 1 PID: 944 Comm: mount Tainted: G            E     5.11.0-rc4-master-19c329f68089 #46
> [44.422030] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-1.fc33 04/01/2014
> [44.427323] RIP: 0010:ext4_process_freed_data+0x74/0x590 [ext4]
> [44.431312] Code: 24 a8 02 00 00 49 8d 8c 24 a8 02 00 00 49 39 c8 74 7f 4c 89 c2 4c 89 c0 31 f6 eb 0e 48 8b 00 48 89 d6 48 39 c8 74 08 48 89 c2 <39> 68 34 74 ed 48 85 f6 74 5d 49 8b 84 24 a8 02 00 00 48 39 c8 74
> [44.442810] RSP: 0018:ffffaeaf00b2ba50 EFLAGS: 00010246
> [44.446185] RAX: 0000000000000000 RBX: ffffaeaf00b2ba78 RCX: ffff9390013ca2a8
> [44.450598] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff9390013ca288
> [44.454723] RBP: 0000000000000006 R08: 0000000000000000 R09: ffff93900443c5b0
> [44.458619] R10: 0000000000000002 R11: 0000000000000000 R12: ffff9390013ca000
> [44.462510] R13: ffff9390013ca288 R14: ffff9390013c8000 R15: ffff939016387fd0
> [44.466103] FS:  00007fe3f7b99c40(0000) GS:ffff9390a7040000(0000) knlGS:0000000000000000
> [44.470061] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [44.472896] CR2: 0000000000000034 CR3: 00000003c305a005 CR4: 0000000000020ee0
> [44.476306] Call Trace:
> [44.477494]  ? __mod_timer+0x25c/0x3d0
> [44.479223]  ext4_journal_commit_callback+0x4a/0xd0 [ext4]
> [44.481807]  jbd2_journal_commit_transaction+0x1a3b/0x1cc0 [jbd2]
> [44.484476]  ? jbd2_journal_destroy+0xc3/0x280 [jbd2]
> [44.486445]  jbd2_journal_destroy+0xc3/0x280 [jbd2]
> [44.488355]  ? finish_wait+0x80/0x80
> [44.489758]  ext4_fill_super+0x2250/0x3bc0 [ext4]
> [44.491651]  ? mount_bdev+0x185/0x1b0
> [44.493083]  ? ext4_calculate_overhead+0x4d0/0x4d0 [ext4]
> [44.495112]  mount_bdev+0x185/0x1b0
> [44.496312]  ? ext4_calculate_overhead+0x4d0/0x4d0 [ext4]
> [44.498173]  legacy_get_tree+0x27/0x40
> [44.499599]  vfs_get_tree+0x25/0xb0
> [44.500786]  path_mount+0x423/0xa40
> [44.501974]  __x64_sys_mount+0xe3/0x120
> [44.503275]  do_syscall_64+0x33/0x40
> [44.504512]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [44.506208] RIP: 0033:0x7fe3f7dcc5de
> 
> --- Call trace End ------------
> 
> # One step Reproducer
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=199179 (reproducer #1)
> https://bugzilla.kernel.org/show_bug.cgi?id=199275 (reproducer #2)
> 
>   mount -o loop 88.img /mnt
> 
> # git bisect log
> 
>   git bisect start
>   # good: [235ecd36c7a93e4d6c73ac71137b8f1fa31148dd] MAINTAINERS: Update my email address
>   git bisect good 235ecd36c7a93e4d6c73ac71137b8f1fa31148dd
>   # bad: [19c329f6808995b142b3966301f217c831e7cf31] Linux 5.11-rc4
>   git bisect bad 19c329f6808995b142b3966301f217c831e7cf31
>   # good: [f97844f9c518172f813b7ece18a9956b1f70c1bb] dt-bindings: net: renesas,etheravb: RZ/G2H needs tx-internal-delay-ps
>   git bisect good f97844f9c518172f813b7ece18a9956b1f70c1bb
>   # good: [ea49c88f4071e2bdd55e78987f251ea54aa11004] Merge tag 'mkp-scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/mkp/scsi
>   git bisect good ea49c88f4071e2bdd55e78987f251ea54aa11004
>   # good: [5ee88057889bbca5f5bb96031b62b3756b33e164] Merge tag 'drm-fixes-2021-01-15' of git://anongit.freedesktop.org/drm/drm
>   git bisect good 5ee88057889bbca5f5bb96031b62b3756b33e164
>   # bad: [b45e2da6e444280f8661dca439c1e377761b2877] Merge branch 'akpm' (patches from Andrew)
>   git bisect bad b45e2da6e444280f8661dca439c1e377761b2877
>   # good: [82821be8a2e14bdf359be577400be88b2f1eb8a7] Merge tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux
>   git bisect good 82821be8a2e14bdf359be577400be88b2f1eb8a7
>   # bad: [0bc9bc1d8b2fa0d5a7e2132e89c540099ea63172] Merge tag 'ext4_for_linus_stable' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4
>   git bisect bad 0bc9bc1d8b2fa0d5a7e2132e89c540099ea63172
>   # bad: [23dd561ad9eae02b4d51bb502fe4e1a0666e9567] ext4: use IS_ERR instead of IS_ERR_OR_NULL and set inode null when IS_ERR
>   git bisect bad 23dd561ad9eae02b4d51bb502fe4e1a0666e9567
>   # bad: [2d01ddc86606564fb08c56e3bc93a0693895f710] ext4: save error info to sb through journal if available
>   git bisect bad 2d01ddc86606564fb08c56e3bc93a0693895f710
>   # good: [4392fbc4bab57db3760f0fb61258cb7089b37665] ext4: drop sync argument of ext4_commit_super()
>   git bisect good 4392fbc4bab57db3760f0fb61258cb7089b37665
>   # good: [05c2c00f3769abb9e323fcaca70d2de0b48af7ba] ext4: protect superblock modifications with a buffer lock
>   git bisect good 05c2c00f3769abb9e323fcaca70d2de0b48af7ba
>   # first bad commit: [2d01ddc86606564fb08c56e3bc93a0693895f710] ext4: save error info to sb through journal if available
> 
> Thanks,
> -- 
> Murphy
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR