thr3ads.net - Btrfs devel - State of btrfs on ARM [Aug 2012]

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Lluís Batlle i Rossell

2012-Aug-19 22:13 UTC

State of btrfs on ARM

Hello,

I just tried to mount a btrfs on 3.4.6, on armv5tel, and it wrote an oops.
Should it work on btrfsnext? Anyone working on that, if not?

I tried "mount -o compress=lzo myfile-with-holes /mnt/btrfs".

Here is the full dmesg:
http://viric.name/tmp/btrfs-arm.txt

Thank you,
Lluís.

Excerpt and objdump -d of the function at the top of the stack:
------------[ cut here ]------------
kernel BUG at fs/btrfs/volumes.c:3666!
Internal error: Oops - BUG: 0 [#1] PREEMPT ARM
Modules linked in: btrfs lzo_compress sg fuse ipv6 scsi_wait_scan ums_cypress
dm_mod ext4 jbd2 reiserfs
CPU: 0    Not tainted  (3.4.6 #1)
PC is at btrfs_num_copies+0xe8/0xf4 [btrfs]
LR is at __lookup_extent_mapping+0xc0/0x1f4 [btrfs]
pc : [<bf2004f4>]    lr : [<bf1daa50>]    psr: 60000013
sp : df2dfc48  ip : df2dfbf8  fp : df2dfc74
r10: c5082020  r9 : 00000000  r8 : 00001000
r7 : b8000000  r6 : 00009000  r5 : 00000000  r4 : df2de000
r3 : 00000000  r2 : 00400000  r1 : 00000000  r0 : 00000000
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
Control: 0005317f  Table: 1f384000  DAC: 00000015
Process mount (pid: 29991, stack limit = 0xdf2de270)
Stack: (0xdf2dfc48 to 0xdf2e0000)
fc40:                   00001000 00000000 def0e170 00000000 00000000 df1ad800
fc60: fffffffb bf1bb0a8 df2dfcc4 df2dfc78 bf1bd89c bf20041c 00001000 00000000
fc80: 00000000 00000004 00000004 00000000 cf97b000 00000000 df1ad800 def0e170
fca0: df1ad800 cf97a000 cf97b000 00000000 df1ad800 00000000 df2dfce4 df2dfcc8
fcc0: bf1be084 bf1bd824 00001000 00000002 00000004 00000000 df2dfdec df2dfce8
fce0: bf1c2118 bf1be054 00001000 cf97a000 00000004 00000000 00000000 00000004
fd00: 00001000 10010000 df19f764 00001000 00001000 cf97a630 cf97a6b0 cf97a570
fd20: cf97a530 cf97a4f0 cf97a4b0 cf97a470 cf97a670 cf97a5f0 cf97a5b0 cf97a430
fd40: cf97a3f0 df1ad810 df1ad400 00001000 00001000 cf97a324 000000b8 00000000
fd60: 00000000 00000000 00000000 00000000 cf97a0ac cf97a1a8 cf97a3b0 00000000
fd80: cf97a33c df1a8240 00000004 00000000 df19f600 dea12c00 de89f400 df2dfdb4
fda0: df2dfddc df2dfdb8 c022dcd4 c0243cc4 c057bfb0 df19f764 00000000 00000000
fdc0: 00000000 cf97a000 df19f600 00000001 df33b000 00000000 bf251cec 00000003
fde0: df2dfe94 df2dfdf0 bf192e04 bf1c0fa4 df2dfe1c df2dfe00 c079dd88 df2dfe44
fe00: 00000000 ffffffff c6781a18 00000000 00000000 00000000 dfa952c0 00000000
fe20: df2dfe6c 706f6f6c c00c0030 c00ca210 c023a50c c00cbbb8 df1b26b8 00000000
fe40: c06ad1ac df125189 df12518c dfa952c0 000000d0 df1251a0 dfa952c0 df1a8240
fe60: 00000000 df1251a0 0000000b df1b2640 bf251cec bf251cec 00000000 df33b000
fe80: 00000000 dfa95460 df2dfec4 df2dfe98 c00d4f4c bf192828 00000005 bf251cec
fea0: bf251cec df1b2640 bf251cec dfa952c0 df33b000 00000000 df2dfeec df2dfec8
fec0: c00ef0bc c00d4f38 df33b000 bf251cec dfa95460 df33b000 dfa952c0 00000000
fee0: df2dff14 df2dfef0 c00ef17c c00ef070 df33b000 00000020 00000000 df33b000
ff00: 00000000 dfa952c0 df2dff6c df2dff18 c00f1140 c00ef148 df2dff84 c00094a4
ff20: df2de000 00000000 dea101f0 c4838a00 c009ba5c c009b344 df2dff6c df2dff48
ff40: c00f0bb0 cf97c000 000230a0 c0ed0000 00000000 c00094a4 df2de000 00000000
ff60: df2dffa4 df2dff70 c00f14e0 c00f0cfc df33b000 df2dff80 c00cfa48 dfa95460
ff80: dfa952c0 df33b000 00022ed0 c0ed0000 00022ea8 00000015 00000000 df2dffa8
ffa0: c0009260 c00f145c 00022ed0 c0ed0000 000230a0 00022ea8 00023090 c0ed0000
ffc0: 00022ed0 c0ed0000 00022ea8 00000015 00022e90 beab21b0 00022ea8 000230a0
ffe0: ffffffef beab200c 0000b684 b6ec90d4 60000010 000230a0 1fffe831 1fffec31
[<bf2004f4>] (btrfs_num_copies+0xe8/0xf4 [btrfs]) from [<bf1bd89c>]
(btree_read_extent_buffer_pages.constprop.30+0x88/0x13c [btrfs])
[<bf1bd89c>] (btree_read_extent_buffer_pages.constprop.30+0x88/0x13c
[btrfs]) from [<bf1be084>] (read_tree_block+0x40/0x4c [btrfs])
[<bf1be084>] (read_tree_block+0x40/0x4c [btrfs]) from [<bf1c2118>]
(open_ctree+0x1184/0x18d4 [btrfs])
[<bf1c2118>] (open_ctree+0x1184/0x18d4 [btrfs]) from [<bf192e04>]
(btrfs_mount+0x5ec/0xa00 [btrfs])
[<bf192e04>] (btrfs_mount+0x5ec/0xa00 [btrfs]) from [<c00d4f4c>]
(mount_fs+0x24/0xdc)
[<c00d4f4c>] (mount_fs+0x24/0xdc) from [<c00ef0bc>]
(vfs_kern_mount+0x5c/0xd8)
[<c00ef0bc>] (vfs_kern_mount+0x5c/0xd8) from [<c00ef17c>]
(do_kern_mount+0x44/0xe4)
[<c00ef17c>] (do_kern_mount+0x44/0xe4) from [<c00f1140>]
(do_mount+0x454/0x730)
[<c00f1140>] (do_mount+0x454/0x730) from [<c00f14e0>]
(sys_mount+0x94/0xd4)
[<c00f14e0>] (sys_mount+0x94/0xd4) from [<c0009260>]
(ret_fast_syscall+0x0/0x2c)
Code: e1a00004 e24bd024 e89dabf0 e7f001f2 (e7f001f2) 
---[ end trace a202a06e5e402bbe ]---


0007440c <btrfs_num_copies>:
   7440c:       e1a0c00d        mov     ip, sp
   74410:       e92ddbf0        push    {r4, r5, r6, r7, r8, r9, fp, ip, lr, pc}
   74414:       e24cb004        sub     fp, ip, #4
   74418:       e24dd008        sub     sp, sp, #8
   7441c:       e92d4000        push    {lr}
   74420:       ebfffffe        bl      0 <__gnu_mcount_nc>
   74424:       e1a0100d        mov     r1, sp
   74428:       e3c14d7f        bic     r4, r1, #8128   ; 0x1fc0
   7442c:       e3c4403f        bic     r4, r4, #63     ; 0x3f
   74430:       e5941004        ldr     r1, [r4, #4]
   74434:       e1a06002        mov     r6, r2
   74438:       e1a07003        mov     r7, r3
   7443c:       e2811001        add     r1, r1, #1
   74440:       e5841004        str     r1, [r4, #4]
   74444:       e1cb80d4        ldrd    r8, [fp, #4]
   74448:       e1cd80f0        strd    r8, [sp]
   7444c:       ebfffffe        bl      4eb84 <lookup_extent_mapping>
   74450:       e1a05000        mov     r5, r0
   74454:       e5943004        ldr     r3, [r4, #4]
   74458:       e2433001        sub     r3, r3, #1
   7445c:       e5843004        str     r3, [r4, #4]
   74460:       e5943000        ldr     r3, [r4]
   74464:       e3130002        tst     r3, #2
   74468:       1a000022        bne     744f8 <btrfs_num_copies+0xec>
   7446c:       e3550000        cmp     r5, #0
   74470:       0a00001f        beq     744f4 <btrfs_num_copies+0xe8>
   74474:       e1c501d0        ldrd    r0, [r5, #16]
   74478:       e1570001        cmp     r7, r1
   7447c:       01560000        cmpeq   r6, r0
   74480:       3a00001a        bcc     744f0 <btrfs_num_copies+0xe4>
   74484:       e1c521d8        ldrd    r2, [r5, #24]
   74488:       e0922000        adds    r2, r2, r0
   7448c:       e0a33001        adc     r3, r3, r1
   74490:       e1530007        cmp     r3, r7
   74494:       01520006        cmpeq   r2, r6
   74498:       3a000014        bcc     744f0 <btrfs_num_copies+0xe4>
   7449c:       e595103c        ldr     r1, [r5, #60]   ; 0x3c
   744a0:       e3a02030        mov     r2, #48 ; 0x30
   744a4:       e3a03000        mov     r3, #0
   744a8:       e1c160d0        ldrd    r6, [r1]
   744ac:       e0022006        and     r2, r2, r6
   744b0:       e0033007        and     r3, r3, r7
   744b4:       e1920003        orrs    r0, r2, r3
   744b8:       15914018        ldrne   r4, [r1, #24]
   744bc:       1a000006        bne     744dc <btrfs_num_copies+0xd0>
   744c0:       e3a02040        mov     r2, #64 ; 0x40
   744c4:       e3a03000        mov     r3, #0
   744c8:       e0022006        and     r2, r2, r6
   744cc:       e0033007        and     r3, r3, r7
   744d0:       e1920003        orrs    r0, r2, r3
   744d4:       1591401c        ldrne   r4, [r1, #28]
   744d8:       03a04001        moveq   r4, #1
   744dc:       e1a00005        mov     r0, r5
   744e0:       ebfffffe        bl      4e7b8 <free_extent_map>
   744e4:       e1a00004        mov     r0, r4
   744e8:       e24bd024        sub     sp, fp, #36     ; 0x24
   744ec:       e89dabf0        ldm     sp, {r4, r5, r6, r7, r8, r9, fp, sp, pc}
   744f0:       e7f001f2        .word   0xe7f001f2
   744f4:       e7f001f2        .word   0xe7f001f2
   744f8:       ebfffffe        bl      0 <preempt_schedule>
   744fc:       eaffffda        b       7446c <btrfs_num_copies+0x60>
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Lluís Batlle i Rossell

2012-Sep-15 11:02 UTC

head link

Re: State of btrfs on ARM

On Mon, Aug 20, 2012 at 12:13:35AM +0200, Lluís Batlle i Rossell
wrote:> Hello,
> 
> I just tried to mount a btrfs on 3.4.6, on armv5tel, and it wrote an oops.
> Should it work on btrfsnext? Anyone working on that, if not?
> 
> I tried "mount -o compress=lzo myfile-with-holes /mnt/btrfs".
After investigating a bit, I saw the problem is related to running
''mkfs.btrfs''
on ARM. If ''mkfs.btrfs'' is run on another platform, it works
fine.

But, the problem appears only if the ARM system has "unaligned access
kernel
traps" disabled for userland code. That happens to be set by default, it
seems.
Setting the kernel to fixup userland unaligned accesses (echo 3 >
/proc/cpu/alignment, for exmaple), then mkfs.btrfs works fine.

I think the kernel mode code has *always* unaligned access fixup, while userland
code is disabled by default. That''d explain the same code was harmless
in the
kernel, while it was failing on userland (on a system without fixup enabled).

Nevertheless, those kernel traps on unaligned accesses are very unefficient. So
the best would be to get gcc generate proper code.

There was a slightly dirty patch sent to this list, to avoid gcc generating
instructions that do unaligned accesses:
http://www.spinics.net/lists/linux-btrfs/msg16007.html

I don''t know the best way to solve that problem; I think that gcc
assumes that
structs are always on unaligned places, and so generates code as if all pointers
to structs are properly aligned. I think that ''memcpy'' (gcc
builtin) may run
faster than the trap, there. But how to write something faster than a memcpy
call, I don''t know.

In fact, looking at the counter of traps run in system-mode in
/proc/cpu/alignment, it increases a lot at every operation I run, either it
writes to btrfs or not. So there should be quite a big amount of code saved by
traps, in the kernel.

Regards,
Lluís.
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Btrfs devel - Aug 2012 - State of btrfs on ARM

State of btrfs on ARM

Re: State of btrfs on ARM