Re: How does the disk buffer cache work?

[Andrew Morton]

Matthew Zahorik wrote:
> 
> Earlier I wrote to the list where my SS10 hung on the partition check
> if a bad disk was installed.
> 
> This behavior is new to the 2.4.20 kernel.  I previously ran 2.2.20 on the
> machine. (the default in a Debian 3.0r0 install)  I can't vouch for 2.4
> kernels previous to 2.4.20.
> 
> I have traced the problem to a hang in the one of the disk buffer caches.
> 
> Can anyone tell me how to correct the behavior so that I:
> 
> 1.  Don't break things for other parts of the kernel
> 2.  The disk cache will return with an error for a hung disk?
> 
> Here's the tail of the console with debugging printk's inserted:
> 
> ...
> [.. the next function call in read_cache_page() is lock_page(), which we
> hang forever on ..]

lock_page() will sleep until the page is unlocked.  The page is unlocked
from end_buffer_io_sync(), which is called from within the context of
the disk device driver's interrupt handler.

This is probably a device driver or interrupt routing problem: the disk
controller hardware interrupts are not making it through to the CPU.