Re: Freeze after disabling write cache with hdparm -W0 /dev/sda

[Tejun Heo <htejun@gmail.com>]

Simon Farnsworth wrote:
> Hello,
> 
> We're trying to consistently disable write caching on our systems (one
> PATA disk on /dev/sda), by running the following command during boot:
> 
> hdparm -W0 /dev/sda
> 
> However, on some disks, we see a freeze of between 30 seconds and 2
> minutes after issuing this command. How do we avoid this freeze? We're
> happy to write our own userspace utility, or change the kernel.
> 
> We're using the pata_via driver, with a kernel that's the same code as
> the Fedora 3189 kernel, but with CONFIG_DEBUG_STACKOVERFLOW set to n.
> 
> From a machine that's just done this freeze:
[--snip--]
> BUG: warning at kernel/softirq.c:138/local_bh_enable() (Not tainted)
>  [<c042afff>] local_bh_enable+0x45/0x96
>  [<c0603cde>] cond_resched_softirq+0x2d/0x43
>  [<c05d55bf>] established_get_first+0x17/0xac
>  [<c05d8f93>] tcp_seq_next+0x71/0x86
>  [<c048c004>] seq_read+0x181/0x268
>  [<c048be83>] seq_read+0x0/0x268
>  [<c0476651>] vfs_read+0xab/0x15a
>  [<c0476fb7>] sys_read+0x41/0x67
>  [<c0404ecc>] syscall_call+0x7/0xb
>  =======================

Hmmmm.. This is the only suspicious looking part of the kernel log and
doesn't have too much to do with ATA freeze.  30sec - 2min delay sounds
awfully like something caused by ATA commands timing out but libata
always complains verbosely about those.  Can you check dmesg again after
the freeze?

-- 
tejun