make-bcache bug?

make-bcache bug?

[Marc MERLIN]

bcache-tools (1.0.8-2+b1)

gargamel:~# make-bcache  -C /dev/sde2
Already a bcache device on /dev/sde2, overwrite with --wipe-bcache
gargamel:~# make-bcache  --wipe-bcache -C /dev/sde2 
Device /dev/sde2 already has a non-bcache superblock, remove it using wipefs and wipefs -a

/dev/sde2 is an old bcache I'm reformatting.
The first message is correct
The 2nd one is not "/dev/sde2 already has a non-bcache superblock"

Clearly it can't have a bcache and not a bcache superblock, right?

Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/                         | PGP 1024R/763BE901

Re: make-bcache bug?

[Marc MERLIN]

On Sun, May 14, 2017 at 10:58:40AM -0700, Marc MERLIN wrote:
> bcache-tools (1.0.8-2+b1)
> 
> gargamel:~# make-bcache  -C /dev/sde2
> Already a bcache device on /dev/sde2, overwrite with --wipe-bcache
> gargamel:~# make-bcache  --wipe-bcache -C /dev/sde2 
> Device /dev/sde2 already has a non-bcache superblock, remove it using wipefs and wipefs -a
> 
> /dev/sde2 is an old bcache I'm reformatting.
> The first message is correct
> The 2nd one is not "/dev/sde2 already has a non-bcache superblock"
> 
> Clearly it can't have a bcache and not a bcache superblock, right?
 
Interesting, same problem/bug with -B:
gargamel:~# make-bcache -B /dev/md8 
Already a bcache device on /dev/md8, overwrite with --wipe-bcache
gargamel:~# make-bcache --wipe-bcache -B /dev/md8 
Device /dev/md8 already has a non-bcache superblock, remove it using wipefs and wipefs -a

Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/                         | PGP 1024R/763BE901

Still have a problem registering cache devices without rebooting :(

[Marc MERLIN]

On Sun, May 14, 2017 at 11:01:26AM -0700, Marc MERLIN wrote:
> On Sun, May 14, 2017 at 10:58:40AM -0700, Marc MERLIN wrote:
> > bcache-tools (1.0.8-2+b1)
> > 
> > gargamel:~# make-bcache  -C /dev/sde2
> > Already a bcache device on /dev/sde2, overwrite with --wipe-bcache
> > gargamel:~# make-bcache  --wipe-bcache -C /dev/sde2 
> > Device /dev/sde2 already has a non-bcache superblock, remove it using wipefs and wipefs -a
> > 
> > /dev/sde2 is an old bcache I'm reformatting.
> > The first message is correct
> > The 2nd one is not "/dev/sde2 already has a non-bcache superblock"
> > 
> > Clearly it can't have a bcache and not a bcache superblock, right?
>  
> Interesting, same problem/bug with -B:
> gargamel:~# make-bcache -B /dev/md8 
> Already a bcache device on /dev/md8, overwrite with --wipe-bcache
> gargamel:~# make-bcache --wipe-bcache -B /dev/md8 
> Device /dev/md8 already has a non-bcache superblock, remove it using wipefs and wipefs -a
 
Ok, sorry for the string of messages, now I see this, which is somewhat
related?

bcache: register_cache() error opening sde2: cache_alloc(): -ENOMEM
bcache: register_bcache() error opening /dev/sde2: (null)
bcache-register: page allocation failure: order:7, mode:0x14080c0(GFP_KERNEL|__GFP_ZERO), nodemask=(null)
bcache-register cpuset=/ mems_allowed=0
CPU: 2 PID: 3121 Comm: bcache-register Tainted: G     U  W       4.11.0-amd64-preempt-sysrq-20170406 #2
Hardware name: System manufacturer System Product Name/P8H67-M PRO, BIOS 3904 04/27/2013
Call Trace:
 dump_stack+0x61/0x7d
 warn_alloc+0xfc/0x18c
 __alloc_pages_slowpath+0xa7e/0xb31
 ? get_page_from_freelist+0x505/0x6a8
 __alloc_pages_nodemask+0x12c/0x1e0
 alloc_pages_current+0x9b/0xbd
 __get_free_pages+0xe/0x35
 register_bcache+0xf0a/0x13d1 [bcache]
 ? alloc_set_pte+0x2e6/0x380
 ? slab_pre_alloc_hook+0x1a/0x44
 kobj_attr_store+0x10/0x1c
 ? kobj_attr_store+0x10/0x1c
 sysfs_kf_write+0x3b/0x3d
 kernfs_fop_write+0xfd/0x144
 __vfs_write+0x35/0xc8
 ? security_file_permission+0x3b/0x42
 vfs_write+0xaf/0xf7
 SyS_write+0x5c/0x9f
 do_fast_syscall_32+0xb7/0xfe
 entry_SYSENTER_compat+0x4c/0x5b
RIP: 0023:0xf7737b39
RSP: 002b:00000000ffca57c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000004
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000583e6008
RDX: 000000000000000a RSI: 00000000ffca5894 RDI: 000000000000000a
RBP: 00000000583e6008 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Mem-Info:
active_anon:102432 inactive_anon:140679 isolated_anon:0
 active_file:2482347 inactive_file:329482 isolated_file:0
 unevictable:1522 dirty:1487 writeback:0 unstable:0
 slab_reclaimable:2289907 slab_unreclaimable:180271
 mapped:32166 shmem:919 pagetables:3727 bounce:0
 free:350647 free_pcp:552 free_cma:0
Node 0 active_anon:408268kB inactive_anon:562716kB active_file:9929388kB inactive_file:1317928kB unevictable:6088kB isolated(anon):0kB isolated(file):0kB mapped:128956kB dirty:5948kB writeback:0kB shmem:3384kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 0kB writeback_tmp:0kB unstable:0kB pages_scanned:0 all_unreclaimable? no
Node 0 DMA free:15876kB min:168kB low:208kB high:248kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:15972kB managed:15888kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:12kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
lowmem_reserve[]: 0 3185 23768 23768 23768
Node 0 DMA32 free:979656kB min:35280kB low:44100kB high:52920kB active_anon:43200kB inactive_anon:86100kB active_file:631884kB inactive_file:358364kB unevictable:88kB writepending:4kB present:3362068kB managed:3283056kB mlocked:88kB slab_reclaimable:1061952kB slab_unreclaimable:80680kB kernel_stack:768kB pagetables:1512kB bounce:0kB free_pcp:232kB local_pcp:0kB free_cma:0kB
lowmem_reserve[]: 0 0 20583 20583 20583
Node 0 Normal free:404000kB min:226688kB low:283360kB high:340032kB active_anon:365652kB inactive_anon:476616kB active_file:9297504kB inactive_file:959564kB unevictable:6000kB writepending:6380kB present:21485568kB managed:21093656kB mlocked:6000kB slab_reclaimable:8097676kB slab_unreclaimable:640392kB kernel_stack:11360kB pagetables:13396kB bounce:0kB free_pcp:5332kB local_pcp:736kB free_cma:0kB
lowmem_reserve[]: 0 0 0 0 0
Node 0 DMA: 1*4kB (U) 0*8kB 0*16kB 0*32kB 2*64kB (U) 1*128kB (U) 1*256kB (U) 0*512kB 1*1024kB (U) 1*2048kB (M) 3*4096kB (M) = 15876kB
Node 0 DMA32: 55994*4kB (UME) 23984*8kB (UME) 11042*16kB (UME) 5401*32kB (UME) 1986*64kB (UME) 512*128kB (UM) 85*256kB (UME) 0*512kB 0*1024kB 0*2048kB 0*4096kB = 979752kB
Node 0 Normal: 93707*4kB (UMEH) 3508*8kB (UMEH) 19*16kB (UMH) 13*32kB (H) 5*64kB (H) 6*128kB (H) 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 404700kB
Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
2833531 total pagecache pages
20198 pages in swap cache
Swap cache stats: add 5746713, delete 5727095, find 41192018/42153913
Free swap  = 15283452kB
Total swap = 15616764kB
6215902 pages RAM
0 pages HighMem/MovableOnly
117752 pages reserved
4096 pages cma reserved
0 pages hwpoisoned


That seems like the same old bug again that I'm not able to register a
bcache cache on a running system without rebooting it :(

argamel:/sys/block/bcache32# echo /dev/sde2  > /sys/fs/bcache/register
bash: page allocation failure: order:7, mode:0x14080c0(GFP_KERNEL|__GFP_ZERO), nodemask=(null)
bash cpuset=/ mems_allowed=0
CPU: 5 PID: 17222 Comm: bash Tainted: G     U  W       4.11.0-amd64-preempt-sysrq-20170406 #2
Hardware name: System manufacturer System Product Name/P8H67-M PRO, BIOS 3904 04/27/2013
Call Trace:
 dump_stack+0x61/0x7d
 warn_alloc+0xfc/0x18c
 __alloc_pages_slowpath+0xa7e/0xb31
 ? get_page_from_freelist+0x505/0x6a8
 __alloc_pages_nodemask+0x12c/0x1e0
 alloc_pages_current+0x9b/0xbd
 __get_free_pages+0xe/0x35
 register_bcache+0xf0a/0x13d1 [bcache]
 ? slab_pre_alloc_hook+0x1a/0x44
 kobj_attr_store+0x10/0x1c
 ? kobj_attr_store+0x10/0x1c
 sysfs_kf_write+0x3b/0x3d
 kernfs_fop_write+0xfd/0x144
 __vfs_write+0x35/0xc8
 ? fput+0x16/0x8a
 ? filp_close+0x67/0x71
 ? security_file_permission+0x3b/0x42
 vfs_write+0xaf/0xf7
 SyS_write+0x5c/0x9f
 do_fast_syscall_32+0xb7/0xfe
 entry_SYSENTER_compat+0x4c/0x5b
RIP: 0023:0xf7754b39
RSP: 002b:00000000ffe5a688 EFLAGS: 00000246 ORIG_RAX: 0000000000000004
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00000000092fc408
RDX: 000000000000000a RSI: 00000000f76d7d60 RDI: 000000000000000a
RBP: 00000000092fc408 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Mem-Info:
active_anon:99187 inactive_anon:140700 isolated_anon:0
 active_file:2489556 inactive_file:328139 isolated_file:0
 unevictable:1530 dirty:31 writeback:7600 unstable:0
 slab_reclaimable:2288880 slab_unreclaimable:184331
 mapped:19547 shmem:978 pagetables:3872 bounce:0
 free:297980 free_pcp:1168 free_cma:0
Node 0 active_anon:396748kB inactive_anon:562800kB active_file:9958224kB inactive_file:1312556kB unevictable:6120kB isolated(anon):0kB isolated(file):0kB mapped:78188kB dirty:124kB writeback:30400kB shmem:3912kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 0kB writeback_tmp:0kB unstable:0kB pages_scanned:1 all_unreclaimable? no
Node 0 DMA free:15876kB min:168kB low:208kB high:248kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:15972kB managed:15888kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:12kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
lowmem_reserve[]: 0 3185 23768 23768 23768
Node 0 DMA32 free:892512kB min:35280kB low:44100kB high:52920kB active_anon:52468kB inactive_anon:86248kB active_file:632908kB inactive_file:361632kB unevictable:88kB writepending:1144kB present:3362068kB managed:3283056kB mlocked:88kB slab_reclaimable:1060108kB slab_unreclaimable:98556kB kernel_stack:1680kB pagetables:2860kB bounce:0kB free_pcp:3584kB local_pcp:60kB free_cma:0kB
lowmem_reserve[]: 0 0 20583 20583 20583
Node 0 Normal free:290224kB min:226688kB low:283360kB high:340032kB active_anon:344280kB inactive_anon:476552kB active_file:9325316kB inactive_file:951240kB unevictable:6032kB writepending:29380kB present:21485568kB managed:21093656kB mlocked:6032kB slab_reclaimable:8095412kB slab_unreclaimable:638756kB kernel_stack:11104kB pagetables:12628kB bounce:0kB free_pcp:2232kB local_pcp:252kB free_cma:0kB
lowmem_reserve[]: 0 0 0 0 0
Node 0 DMA: 1*4kB (U) 0*8kB 0*16kB 0*32kB 2*64kB (U) 1*128kB (U) 1*256kB (U) 0*512kB 1*1024kB (U) 1*2048kB (M) 3*4096kB (M) = 15876kB
Node 0 DMA32: 51574*4kB (UME) 20985*8kB (UME) 8562*16kB (UME) 5364*32kB (UME) 1952*64kB (UME) 503*128kB (UM) 86*256kB (UME) 0*512kB 0*1024kB 0*2048kB 0*4096kB = 894144kB
Node 0 Normal: 66404*4kB (EH) 2053*8kB (UMEH) 124*16kB (UMEH) 128*32kB (UMEH) 11*64kB (MEH) 7*128kB (MH) 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 289720kB
Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
2839584 total pagecache pages
20209 pages in swap cache
Swap cache stats: add 5746727, delete 5727098, find 41222108/42184007
Free swap  = 15283452kB
Total swap = 15616764kB
6215902 pages RAM
0 pages HighMem/MovableOnly
117752 pages reserved
4096 pages cma reserved
0 pages hwpoisoned
bcache: register_cache() error opening sde2: cache_alloc(): -ENOMEM
bcache: register_bcache() error opening /dev/sde2: (null)


Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/                         | PGP 1024R/763BE901

Re: make-bcache bug?

[Kai Krakow]

Am Sun, 14 May 2017 10:58:40 -0700
schrieb Marc MERLIN <marc@merlins.org>:

> bcache-tools (1.0.8-2+b1)
> 
> gargamel:~# make-bcache  -C /dev/sde2
> Already a bcache device on /dev/sde2, overwrite with --wipe-bcache
> gargamel:~# make-bcache  --wipe-bcache -C /dev/sde2 
> Device /dev/sde2 already has a non-bcache superblock, remove it using
> wipefs and wipefs -a
> 
> /dev/sde2 is an old bcache I'm reformatting.
> The first message is correct
> The 2nd one is not "/dev/sde2 already has a non-bcache superblock"
> 
> Clearly it can't have a bcache and not a bcache superblock, right?

I don't think that each filesystem puts their superblocks in the same
position. Plus, there are usually backup superblocks across the area.

So you may well see both warnings and both are correct.

Use wipefs, there seems to be an orphan superblock.

-- 
Regards,
Kai

Replies to list-only preferred.

Re: make-bcache bug?

[Marc MERLIN]

On Sun, May 14, 2017 at 10:00:55PM +0200, Kai Krakow wrote:
> Am Sun, 14 May 2017 10:58:40 -0700
> schrieb Marc MERLIN <marc@merlins.org>:
> 
> > bcache-tools (1.0.8-2+b1)
> > 
> > gargamel:~# make-bcache  -C /dev/sde2
> > Already a bcache device on /dev/sde2, overwrite with --wipe-bcache
> > gargamel:~# make-bcache  --wipe-bcache -C /dev/sde2 
> > Device /dev/sde2 already has a non-bcache superblock, remove it using
> > wipefs and wipefs -a
> > 
> > /dev/sde2 is an old bcache I'm reformatting.
> > The first message is correct
> > The 2nd one is not "/dev/sde2 already has a non-bcache superblock"
> > 
> > Clearly it can't have a bcache and not a bcache superblock, right?
> 
> I don't think that each filesystem puts their superblocks in the same
> position. Plus, there are usually backup superblocks across the area.
> 
> So you may well see both warnings and both are correct.
> 
> Use wipefs, there seems to be an orphan superblock.

Doesn't wipefs -a clear just 16 bytes or so?
I did it and it fixed my problem, but this block device was a bcache
before, and of course on top of that bcache I then added a filesystem.

Let's test this.
1) I wipefs'ed it
2) I made a new cache device on top
3) I did not put a filesystem or use it, because registration is broken
and still rquires a reboot
bcache: register_cache() error opening sde2: cache_alloc(): -ENOMEM
bcache: register_bcache() error opening /dev/sde2: (null)

4) recreating a new cache on top fo the unused cache, fails again.
Basically the superblock detection is not working right and detects
bcache as a non bcache superblock.

gargamel:/mnt/btrfs_pool2# make-bcache  -C /dev/sde2
Already a bcache device on /dev/sde2, overwrite with --wipe-bcache
gargamel:/mnt/btrfs_pool2# make-bcache  --wipe-bcache -C /dev/sde2 
Device /dev/sde2 already has a non-bcache superblock, remove it using wipefs and wipefs -a

Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/                         | PGP 1024R/763BE901

Re: make-bcache bug?

[Kai Krakow]

Am Sun, 14 May 2017 13:19:40 -0700
schrieb Marc MERLIN <marc@merlins.org>:

> On Sun, May 14, 2017 at 10:00:55PM +0200, Kai Krakow wrote:
> > Am Sun, 14 May 2017 10:58:40 -0700
> > schrieb Marc MERLIN <marc@merlins.org>:
> >   
> > > bcache-tools (1.0.8-2+b1)
> > > 
> > > gargamel:~# make-bcache  -C /dev/sde2
> > > Already a bcache device on /dev/sde2, overwrite with --wipe-bcache
> > > gargamel:~# make-bcache  --wipe-bcache -C /dev/sde2 
> > > Device /dev/sde2 already has a non-bcache superblock, remove it
> > > using wipefs and wipefs -a
> > > 
> > > /dev/sde2 is an old bcache I'm reformatting.
> > > The first message is correct
> > > The 2nd one is not "/dev/sde2 already has a non-bcache superblock"
> > > 
> > > Clearly it can't have a bcache and not a bcache superblock,
> > > right?  
> > 
> > I don't think that each filesystem puts their superblocks in the
> > same position. Plus, there are usually backup superblocks across
> > the area.
> > 
> > So you may well see both warnings and both are correct.
> > 
> > Use wipefs, there seems to be an orphan superblock.  
> 
> Doesn't wipefs -a clear just 16 bytes or so?
> I did it and it fixed my problem, but this block device was a bcache
> before, and of course on top of that bcache I then added a filesystem.
> 
> Let's test this.
> 1) I wipefs'ed it
> 2) I made a new cache device on top
> 3) I did not put a filesystem or use it, because registration is
> broken and still rquires a reboot
> bcache: register_cache() error opening sde2: cache_alloc(): -ENOMEM
> bcache: register_bcache() error opening /dev/sde2: (null)
> 
> 4) recreating a new cache on top fo the unused cache, fails again.
> Basically the superblock detection is not working right and detects
> bcache as a non bcache superblock.
> 
> gargamel:/mnt/btrfs_pool2# make-bcache  -C /dev/sde2
> Already a bcache device on /dev/sde2, overwrite with --wipe-bcache
> gargamel:/mnt/btrfs_pool2# make-bcache  --wipe-bcache -C /dev/sde2 
> Device /dev/sde2 already has a non-bcache superblock, remove it using
> wipefs and wipefs -a

I had done this previously, too, and had no such message. But I had to
use wipefs anyway because otherwise udev came and triggered the device
for reasons I couldn't really follow.

If you get udev not to interfere with such actions, you usually also do
not need to reboot because unregistration and registration works.

But you can also easily get stuck when you decompose the bcache device
in the wrong way. It will simply stay registered then and cannot be
unregistered because the device is still in use. In that situation I
wouldn't wipefs the device.


-- 
Regards,
Kai

Replies to list-only preferred.

Re: make-bcache bug?

[Nix]

On 14 May 2017, Kai Krakow said:
> I had done this previously, too, and had no such message. But I had to
> use wipefs anyway because otherwise udev came and triggered the device
> for reasons I couldn't really follow.

udev does a blkid to see how the block device needs to be activated:
this relies on precisely the information wipefs removes. Avoiding this
problem is why wipefs *exists*. :)

-- 
NULL && (void)

Re: make-bcache bug?

[Kai Krakow]

Am Mon, 15 May 2017 13:52:09 +0100
schrieb Nix <nix@esperi.org.uk>:

> On 14 May 2017, Kai Krakow said:
> > I had done this previously, too, and had no such message. But I had
> > to use wipefs anyway because otherwise udev came and triggered the
> > device for reasons I couldn't really follow.  
> 
> udev does a blkid to see how the block device needs to be activated:
> this relies on precisely the information wipefs removes. Avoiding this
> problem is why wipefs *exists*. :)

Yes, but something triggered udev when it shouldn't...

This ends up in unregistering/stopping the bcache, then wipefs the
cdev, then look if udev was triggered and eventually stop it again.

I guess everytime I ran "fdisk -l" to double-check the devices, or
"lsblk", or "blkid", udev was triggered and re-enabled the bcache. This
is a race you cannot win. ;-)

-- 
Regards,
Kai

Replies to list-only preferred.

Re: make-bcache bug?

[Marc MERLIN]

On Mon, May 15, 2017 at 08:37:45PM +0200, Kai Krakow wrote:
> Am Mon, 15 May 2017 13:52:09 +0100
> schrieb Nix <nix@esperi.org.uk>:
> 
> > On 14 May 2017, Kai Krakow said:
> > > I had done this previously, too, and had no such message. But I had
> > > to use wipefs anyway because otherwise udev came and triggered the
> > > device for reasons I couldn't really follow.  
> > 
> > udev does a blkid to see how the block device needs to be activated:
> > this relies on precisely the information wipefs removes. Avoiding this
> > problem is why wipefs *exists*. :)
> 
> Yes, but something triggered udev when it shouldn't...
> 
> This ends up in unregistering/stopping the bcache, then wipefs the
> cdev, then look if udev was triggered and eventually stop it again.
> 
> I guess everytime I ran "fdisk -l" to double-check the devices, or
> "lsblk", or "blkid", udev was triggered and re-enabled the bcache. This
> is a race you cannot win. ;-)

Note that this is orthogonal to the problem I reported.
It tells me 
Already a bcache device on /dev/sde2, overwrite with --wipe-bcache
when it fact this does not work, apparently ever.

So either the message gets changed, or 
make-bcache  --wipe-bcache -C /dev/sde2                                               
Device /dev/sde2 already has a non-bcache superblock, remove it using wipefs and wipefs -a
does not happen. there was no non-bcache superblock.

Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/  

Re: make-bcache bug?

[Kai Krakow]

Am Mon, 15 May 2017 17:58:48 -0700
schrieb Marc MERLIN <marc@merlins.org>:

> On Mon, May 15, 2017 at 08:37:45PM +0200, Kai Krakow wrote:
> > Am Mon, 15 May 2017 13:52:09 +0100
> > schrieb Nix <nix@esperi.org.uk>:
> >   
> > > On 14 May 2017, Kai Krakow said:  
>  [...]  
> > > 
> > > udev does a blkid to see how the block device needs to be
> > > activated: this relies on precisely the information wipefs
> > > removes. Avoiding this problem is why wipefs *exists*. :)  
> > 
> > Yes, but something triggered udev when it shouldn't...
> > 
> > This ends up in unregistering/stopping the bcache, then wipefs the
> > cdev, then look if udev was triggered and eventually stop it again.
> > 
> > I guess everytime I ran "fdisk -l" to double-check the devices, or
> > "lsblk", or "blkid", udev was triggered and re-enabled the bcache.
> > This is a race you cannot win. ;-)  
> 
> Note that this is orthogonal to the problem I reported.
> It tells me 
> Already a bcache device on /dev/sde2, overwrite with --wipe-bcache
> when it fact this does not work, apparently ever.
> 
> So either the message gets changed, or 
> make-bcache  --wipe-bcache
> -C /dev/sde2 Device /dev/sde2 already has a non-bcache superblock,
> remove it using wipefs and wipefs -a does not happen. there was no
> non-bcache superblock.

I look at both source codes of wipefs and make-bcache should give a
clue.

Since you made me curious, I'll probably take a look this weekend.


-- 
Regards,
Kai

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