Re: [BUG] mm: bdi: export BDI attributes in sysfs
- From: Arthur Jones <ajones@xxxxxxxxxxxx>
- Date: Wed, 14 May 2008 07:40:30 -0700
Hi Peter, Andrew Morton asked that I add some
details and a lkml cc: to this bug report.
This problem showed up in a test I have which
uses the ipmitool to repeatedly cycle power on
3 SATA disks connected to an AHCI controller:
00:1f.2 SATA controller: Intel Corporation: Unknown device 2922 (rev 02)
(prog-)
Subsystem: Tyan Computer: Unknown device 6631
Flags: bus master, 66Mhz, medium devsel, latency 0, IRQ 511
I/O ports at fc00 [size=8]
I/O ports at f880 [size=4]
I/O ports at f800 [size=8]
I/O ports at f480 [size=4]
I/O ports at f400 [size=32]
Memory at fdfff800 (32-bit, non-prefetchable) [size=2K]
Capabilities: [80] Message Signalled Interrupts: 64bit- Queue=0/4 Enabl+
Capabilities: [70] Power Management version 3
Capabilities: [a8] #12 [0010]
Capabilities: [b0] #13 [0306]
About 1 in 4 times, when turning the power back
on for a drive, I get the BUG reported below. The
drives are not mounted, just sitting there getting
power cycled (the test looks to make sure they are
being seen by the scsi subsystem and udev).
The ipmitool command which powers off disks 2 and 3 is:
ipmitool raw 0x06 0x52 0x07 0x36 0x00 0x01 0xfb
ipmitool raw 0x06 0x52 0x07 0x36 0x00 0x01 0xf7
The ipmitool command which powers on all disks is:
ipmitool raw 0x06 0x52 0x07 0x36 0x00 0x01 0xff
Though I expect these commands are not likely to
work anywhere but on the systems we have here...
Arthur
On Tue, May 13, 2008 at 12:04:35PM -0700, Arthur Jones wrote:
Hi Peter, When powering down then back up SATA drives
on my box I found a BUG in the read_ahead_kb_show bdi
device attribute code. Somehow (I never tracked down
why), the bdi is NULL occassionally in this code when
running my test. I'm not sure the right way to fix
it, but the attached patch no longer causes the bug
after many power cycles...
This code appeared in Linus' tree via:
commit cf0ca9fe5dd9e3693d935757a7b2fc50fc576554
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Date: Wed Apr 30 00:54:32 2008 -0700
mm: bdi: export BDI attributes in sysfs
Provide a place in sysfs (/sys/class/bdi) for the backing_dev_info object.
This allows us to see and set the various BDI specific variables.
[...]
The backtrace was:
BUG: unable to handle kernel NULL pointer dereference at
0000000000000000
IP: [<ffffffff802694e3>] read_ahead_kb_show+0x1b/0x2d
PGD df92c067 PUD df92b067 PMD 0
Oops: 0000 [1] SMP
CPU 0
Modules linked in: iptable_mangle ip_tables x_tables ipmi_devintf
ipmi_watchdoge
Pid: 12752, comm: udev Tainted: GF 2.6.26-rc2SMP #5
RIP: 0010:[<ffffffff802694e3>] [<ffffffff802694e3>]
read_ahead_kb_show+0x1b/0xd
RSP: 0018:ffff8100778a1e98 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffffffff8066a4e0 RCX: 0000000000000000
RDX: ffffffff805eb4cf RSI: 0000000000000fff RDI: ffff810099cbf000
RBP: fffffffffffffffb R08: ffff810099cbf000 R09: 000000000009b25f
R10: 0000000000000000 R11: 0000000000000002 R12: ffff810099dd5870
R13: ffffffff80682ec0 R14: ffff8100778a1f50 R15: 0000000000000000
FS: 00007fed77fff6e0(0000) GS:ffffffff806ca000(0000)
knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000000 CR3: 00000000df929000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process udev (pid: 12752, threadinfo ffff8100778a0000, task
ffff81011e274800)
Stack: ffff81011fc02093 ffffffff803d88ea 0000000000000000
ffff81011ddcc930
ffff81011e7c9780 ffffffff802cd2f9 0000000000000000 0000000000001000
000000000054bad0 ffff81009891a600 0000000000001000 000000000054bad0
Call Trace:
[<ffffffff803d88ea>] ? dev_attr_show+0x1f/0x41
[<ffffffff802cd2f9>] ? sysfs_read_file+0xa5/0x128
[<ffffffff80286fca>] ? vfs_read+0xab/0x12e
[<ffffffff802872ce>] ? sys_read+0x45/0x6e
[<ffffffff8020b14b>] ? system_call_after_swapgs+0x7b/0x80
Code: e5 48 89 45 00 5a 5b 5d 41 5c 4c 89 e8 41 5d c3 41 50 48 8b 87 e0
01 00 0
RIP [<ffffffff802694e3>] read_ahead_kb_show+0x1b/0x2d
RSP <ffff8100778a1e98>
CR2: 0000000000000000
---[ end trace 74e8b5443cce1870 ]---
Arthur
mm: bdi: Check for NULL backing device
When powering down then powering up SATA drives,
I found that the bdi would sometimes be NULL in
the dev_get_drvdata(dev). When showing device
attributes, check for this condition to avoid
a NULL pointer dereference.
Signed-off-by: Arthur Jones <ajones@xxxxxxxxxxxx>
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 7c4f9e0..cc9393f 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -109,7 +109,10 @@ static ssize_t name##_show(struct device *dev, \
{ \
struct backing_dev_info *bdi = dev_get_drvdata(dev); \
\
- return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr); \
+ if (!bdi) \
+ return snprintf(page, PAGE_SIZE - 1, "\n"); \
+ else \
+ return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);\
}
BDI_SHOW(read_ahead_kb, K(bdi->ra_pages))
--
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