Re: WARNING: CPU: 0 PID: 1 at fs/block_dev.c:58 __blkdev_put+0x16f/0x1b0()

[Jan Kara <jack@suse.cz>]

  Hi!

On Sat 07-11-15 13:07:30, Richard Weinberger wrote:
> While playing with the Linux kernel library I run into this warning.
> Root cause of the warning is that the backing file on the host
> side is locked an therefore all IO on it results into -EIO.
> 
> The question is whether ext4/jbd2 should abort earlier or not.
> The WARN_ON_ONCE in bdev_write_inode() triggers as jbd2's do_one_pass()
> sets up a dirty buffer_head and fails later.
> Then ext4 gives up, calls blkdev_put() and we reach bdev_write_inode()
> with a dirty ->bd_inode.
> 
> What do you think?

So I think the right question is what we should do when we cannot writeback
dirty data. Currently we WARN_ON in some places (bdev_write_inode() is one
of them) and print errors in others. Although loosing data is nasty, people
seem to remove devices or do similar stuff too often for WARN_ON to be really
an adequate answer... So I think we should just print error message and go
on without spewing stack traces. Thoughts?

								Honza

> [    0.128000] blk_update_request: I/O error, dev vda, sector 0
> [    0.128000] Buffer I/O error on dev vda, logical block 0, lost async page write
> [    0.128000] blk_update_request: I/O error, dev vda, sector 8
> [    0.128000] Buffer I/O error on dev vda, logical block 1, lost async page write
> [    0.128000] blk_update_request: I/O error, dev vda, sector 528
> [    0.128000] Buffer I/O error on dev vda, logical block 66, lost async page write
> [    0.128000] blk_update_request: I/O error, dev vda, sector 1824
> [    0.128000] Buffer I/O error on dev vda, logical block 228, lost async page write
> [    0.128000] blk_update_request: I/O error, dev vda, sector 1864
> [    0.128000] Buffer I/O error on dev vda, logical block 233, lost async page write
> [    0.128000] blk_update_request: I/O error, dev vda, sector 41840
> [    0.128000] Buffer I/O error on dev vda, logical block 5230, lost async page write
> [    0.128000] blk_update_request: I/O error, dev vda, sector 262672
> [    0.128000] Buffer I/O error on dev vda, logical block 32834, lost async page write
> [    0.128000] blk_update_request: I/O error, dev vda, sector 262680
> [    0.128000] Buffer I/O error on dev vda, logical block 32835, lost async page write
> [    0.128000] blk_update_request: I/O error, dev vda, sector 262752
> [    0.128000] Buffer I/O error on dev vda, logical block 32844, lost async page write
> [    0.128000] blk_update_request: I/O error, dev vda, sector 262792
> [    0.128000] Buffer I/O error on dev vda, logical block 32849, lost async page write
> [    0.132000] JBD2: recovery failed
> [    0.132000] EXT4-fs (vda): error loading journal
> [    0.132000] ------------[ cut here ]------------
> [    0.132000] WARNING: CPU: 0 PID: 1 at fs/block_dev.c:58 __blkdev_put+0x16f/0x1b0()
> [    0.132000] Call Trace:
> [    0.132000] 00007fd99262db68:  [<0040673d>] warn_slowpath_common+0x7d/0xb0
> [    0.132000] 00007fd99262dba8:  [<004068d5>] warn_slowpath_null+0x15/0x20
> [    0.132000] 00007fd99262dbb8:  [<0048efbf>] __blkdev_put+0x16f/0x1b0
> [    0.132000] 00007fd99262dbf8:  [<0048fcd2>] blkdev_put+0x92/0x110
> [    0.132000] 00007fd99262dc28:  [<00462faf>] kill_block_super+0x3f/0x70
> [    0.132000] 00007fd99262dc48:  [<00461bf2>] deactivate_locked_super+0x52/0xb0
> [    0.132000] 00007fd99262dc78:  [<00462f51>] mount_bdev+0x1b1/0x1d0
> [    0.132000] 00007fd99262dc80:  [<004c5c40>] ext4_fill_super+0x0/0x32f0
> [    0.132000] 00007fd99262dce8:  [<004c16f0>] ext4_mount+0x10/0x20
> [    0.132000] 00007fd99262dcf8:  [<00463164>] mount_fs+0x14/0xc0
> [    0.132000] 00007fd99262dd28:  [<0047a38e>] vfs_kern_mount+0x5e/0x120
> [    0.132000] 00007fd99262dd78:  [<0047baa8>] do_mount+0x208/0xd90
> [    0.132000] 00007fd99262dd88:  [<0045d7db>] __kmalloc_track_caller+0x18b/0x1c0
> [    0.132000] 00007fd99262dd98:  [<00450618>] strndup_user+0x48/0x60
> [    0.132000] 00007fd99262de08:  [<00450618>] strndup_user+0x48/0x60
> [    0.132000] 00007fd99262de48:  [<0047c99a>] SyS_mount+0x6a/0xb0
> [    0.132000] 00007fd99262de98:  [<00403b89>] run_syscalls+0xd9/0x1c0
> [    0.132000] 00007fd99262deb0:  [<00425970>] autoremove_wake_function+0x0/0x40
> [    0.132000] 00007fd99262dec8:  [<005535f0>] kernel_init+0x0/0xf0
> [    0.132000] 00007fd99262dee8:  [<005535f0>] kernel_init+0x0/0xf0
> [    0.132000] 00007fd99262df08:  [<00402f2d>] run_init_process+0x1d/0x40
> [    0.132000] 00007fd99262df18:  [<00553626>] kernel_init+0x36/0xf0
> [    0.132000] 00007fd99262df28:  [<00403158>] thread_bootstrap+0x48/0x50
> [    0.132000]
> [    0.132000] ---[ end trace 0b886a9a044a4995 ]---
> 
> Thanks,
> //richard
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR