Re: Asking for path to modules (was: How do I keep testing current-amd64 witout so much trouble?)

[christos%zoulas.com@localhost (Christos Zoulas)]

On Dec 26, 10:49am, paul%whooppee.com@localhost (Paul Goyette) wrote:
-- Subject: Re: Asking for path to modules (was: How do I keep testing curren

| On Fri, 26 Dec 2008, Christos Zoulas wrote:
| 
| > On Dec 26,  7:09am, paul%whooppee.com@localhost (Paul Goyette) wrote:
| > -- Subject: Re: Asking for path to modules (was: How do I keep testing 
curren
| >
| > | On Thu, 25 Dec 2008, Christos Zoulas wrote:
| > |
| > | > Try a lockdebug kernel. I get spinouts when I do that.
| > |
| > | The crash happens shortly after (within 1 to 5 seconds) the prompt for
| > | root device is printed, and does not matter if I've typed a character or
| > | not.  I'm unable to get a crash dump, since both "sync" and "reboot
| > | 0x100" hang after printing the message "syncing disks...".
| > |
| > | Information from the spinout, manually annotated with kernel addresses
| > | decoded using GDB.
| > |
| > | lock address: ffffffff80594c40     type:                   spin
| > |                == kernel_lock
| > | initialized:  ffffffff801a6097
| > |                == main + 0x27
| > | shared holds:                0     exclusive:                 1
| > | shares wanted:               0     exclusive:                 1
| > | current cpu:                 0     last held:                 3
| > | current lwp:  ffff80004b2aa000     last held:  ffffffff80552d60
| > |                                                 == lwp0
| > | last locked:  ffffffff801f9d0d     unlocked:   ffffffff801ae68b
| > |                == sleepq_block + x18d       == intr_biglock_wrapper+x2b
| > | curcpu holds:                0
| > |
| > | So, it seems that something is holding onto the kernel's biglock and
| > | sleeping, while the init process wants the lock and isn't willing to
| > | wait for it?
| > |
| > | Question:  Does cngetsn() take out the kernel's biglock?  It does not
| > | appear to do so at first glance.
| >
| > I don't know. but I think that the simplest solution for LOCKDEBUG
| > kernels is to avoid the issue by not allowing spinouts while we
| > are sleeping for input, using a global variable. It is ugly, but I
| > don't have a better idea right now.
| 
| That would take care of the LOCKDEBUG kernel panic, but wouldn't deal 
| with the real problem, at least not _my_ real problem:
| 
|       something (lastheld == lwp0 ?) appears to be holding onto
|       kernel_lock while cngetsn() is trying to wait for input and
|       wants the lock.
| 
| What I really don't understand is why the addition of a single printf() 
| and a single cngetsn() call very early in life (module_init() is one of 
| the earliest things to be called by main()) leaves things in such a 
| confused state by the time we get around to calling vfs_mountroot().
| 
| I'm going to see if some extra printf()s can help me make some forward 
| progress.

Right but perhaps it will tell you where the kernel lock was held from.

christos