Oops when writing to /sys/block/ram0/queue/max_sectors_kb

[Jens Rosenboom]

Even when writing the current value again, I get this Oops and further
reads from that file stall.

# cat /sys/block/ram0/queue/max_sectors_kb 
512
# echo 512 >/sys/block/ram0/queue/max_sectors_kb
[Produces an Oops and connection closes]
[After logging in again:]
# cat /sys/block/ram0/queue/max_sectors_kb
[hangs]

Corresponding output from dmesg:

[ 1254.984435] BUG: unable to handle kernel NULL pointer dereference at
(null)
[ 1254.988005] IP: [<c12a1550>] _spin_lock_irq+0x10/0x30
[ 1254.988005] *pde = 00000000 
[ 1254.988005] Oops: 0002 [#1] SMP 
[ 1254.988005] last sysfs
file: /sys/devices/virtual/block/ram0/queue/max_sectors_kb
[ 1254.988005] Modules linked in: ipv6 af_packet usbhid hid uhci_hcd
ohci_hcd ehci_hcd usbcore 8021q garp stp serio_raw psmouse evdev
i2c_piix4 button container pcspkr processor i2c_core ext3 jbd mbcache
dm_mirror dm_region_hash dm_log dm_snapshot dm_mod raid10 raid456
raid6_pq async_xor async_memcpy async_tx xor raid1 raid0 multipath
linear md_mod sg sr_mod cdrom ata_generic pata_acpi pata_serverworks
megaraid libata floppy e100 mii scsi_mod cpqarray thermal fan
[ 1254.988005] 
[ 1254.988005] Pid: 3822, comm: bash Not tainted (2.6.31-rc4 #3)
ProLiant DL360
[ 1254.988005] EIP: 0060:[<c12a1550>] EFLAGS: 00010012 CPU: 0
[ 1254.988005] EIP is at _spin_lock_irq+0x10/0x30
[ 1254.988005] EAX: 00000100 EBX: 00000004 ECX: c379e003 EDX: 00000000
[ 1254.988005] ESI: 00000200 EDI: f6bb0000 EBP: c3605f00 ESP: c3605f00
[ 1254.988005]  DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
[ 1254.988005] Process bash (pid: 3822, ti=c3604000 task=f6bde800
task.ti=c3604000)
[ 1254.988005] Stack:
[ 1254.988005]  c3605f1c c115d93b 00000004 c379e003 f6bb0000 f6bb0470
c13ca238 c3605f34
[ 1254.988005] <0> c115d9a7 c379e000 f707c7e0 c13ca1ac f69bf5c0 c3605f64
c111408d 00000004
[ 1254.988005] <0> 00000004 08e99408 f6976480 f69bf5d4 c13ca1ac f6bb0148
f6976480 08e99408
[ 1254.988005] Call Trace:
[ 1254.988005]  [<c115d93b>] ? queue_max_sectors_store+0x5b/0x80
[ 1254.988005]  [<c115d9a7>] ? queue_attr_store+0x47/0x70
[ 1254.988005]  [<c111408d>] ? sysfs_write_file+0x9d/0xf0
[ 1254.988005]  [<c10c889c>] ? vfs_write+0x9c/0x180
[ 1254.988005]  [<c1113ff0>] ? sysfs_write_file+0x0/0xf0
[ 1254.988005]  [<c10c8a3d>] ? sys_write+0x3d/0x70
[ 1254.988005]  [<c1003049>] ? syscall_call+0x7/0xb
[ 1254.988005] Code: 01 00 00 f0 66 0f c1 02 38 e0 74 06 f3 90 8a 02 eb
f6 89 c8 5d c3 90 8d 74 26 00 55 89 c2 89 e5 fa 90 8d 74 26 00 b8 00 01
00 00 <f0> 66 0f c1 02 38 e0 74 06 f3 90 8a 02 eb f6 5d c3 eb 0d 90 90 
[ 1254.988005] EIP: [<c12a1550>] _spin_lock_irq+0x10/0x30 SS:ESP
0068:c3605f00
[ 1254.988005] CR2: 0000000000000000
[ 1254.988005] ---[ end trace ee0e56d1adcbecab ]---


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