The problem I am seeking help on is not an ALSA problem per-se, but as I am
working on an ALSA driver I thought I'd start here...
any suggestions for a more appropriate forum will be gratefully accepted.
Background info:
I have a lowlevel driver that works fine when I used semaphores to prevent
conention for my hardware. Access was soley via ioctl into my driver.
I have to change the semaphore to a spinlock now that I also call basically the
same entry point from a timer routine in my ALSA driver.
When I record from the card the data is read from the card into a userspace
buffer
ptr,size = <Buffer pointer,size received from user application>
fs = get_fs();
set_fs(get_ds());
/* Ensure that the data buffer is resident in memory. */
if (!access_ok (wrflag ? VERIFY_WRITE : VERIFY_READ, ptr, bytes))
{
set_fs(fs);
return -EFAULT;
}
/* Inside here is the spinlock, and a copy to the ptr mentioned above */
HPI_MessageF (gphHpiSubsys, &hm, &hr, file );
set_fs(fs);
Problem:
The single change from semaphore to spinlock results in a kernel panic when I
try to record from my card:
Unable to handle kernel paging request at virtual address ...
Question:
Notwithstanding bad style etc, am I doing something that is fundamentally wrong
in using a userspace buffer when I am inside a spinlock i.e. in interrupt
context? (In the same way as I must not use a semaphore in interrupt context)
Could it be that when I try to write to the buffer it causes a page fault, which
cannot be handled in interrupt context?
But I thought that access_ok call should take care of making sure the buffer is
in memory...
TIA for any insights you may have.
Eliot Blennerhassett
AudioScience Inc.
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