Lawrence Stewart <[EMAIL PROTECTED]> writes: > Dag-Erling Smørgrav <[EMAIL PROTECTED]> writes: > > Since you are writing kernel code, I assume you have KDB/DDB in your > > kernel and know how to use it. > I don't know how to use them really. Thus far I haven't had a need for > really low level debugging tools... seems that may have changed > though! Any good tutorials/pointers on how to get started with kernel > debugging?
The handbook and FAQ have information on debugging panics. Greg Lehey (grog@) does a tutorial on kernel debugging, you can probably find slides online (or just ask him) > > kio_write probably blocks waiting for the write to complete. You can't > > do that while holding a non-sleepable lock. > So this is where my knowledge/understanding gets very hazy... > > When a thread blocks waiting for some operation to complete or event > to happen, the thread effectively goes to sleep, correct? It depends on the type of lock used, but mostly, yes. > Looking at the kio_write code in subr_kernio.c, I'm guessing the lock > that is causing the trouble is related to the "vn_lock" function call? What matters is that kio_write() may sleep and therefore can't be called while holding a non-sleepable lock. > I don't understand though why the vnode lock would be set up in such a > way that when the write blocks whilst waiting for the underlying > filesystem to signal everything is ok, it causes the kernel to panic! You cannot sleep while holding a non-sleepable lock. You need to find out which locks are held at the point where you call kio_write(), and figure out a way to delay the kio_write() call until those locks are released. > How do I make the lock "sleepable" or make sure the thread doesn't try > go to sleep whilst holding the lock? You can't make an unsleepable lock sleepable. You might be able to replace it with a sleepable lock, but you would have to go through every part of the kernel that uses the lock and make sure that it works correctly with a sleepable lock. Most likely, it won't. DES -- Dag-Erling Smørgrav - [EMAIL PROTECTED] _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
