Re: PANIC: blockable slep lock (sx) msi _at_ ....msi.c:374

On Friday 04 May 2007 10:53:27 pm Attilio Rao wrote:
> Harald Schmalzbauer wrote:
> > Hello,
> > 
> > recent changes (during the last 2 days,I guess tha acpi stuff) broke 
> > -current for me:
> > 
> > ad6: 476940MB <WDC WD5000KS-07MNB0 07.02E07> at ata3-master SATA300
> > SMP: AP CPU #1 Launched!
> > panic: blockable sleep lock (sx) msi _at_ 
> > /FlashBSD/src/sys/i386/i386/msi.c:374
> > cpuid = 0
> > KDB: enter: panic
> > [thread pid 0 tid 0 ]
> > Stopped at      kdb_enter+0x30: leave
> > db> bt
> > Tracing pid 0 tid 0 td 0xc07c2d60
> > kdb_enter(c07422df,0,c0746e47,c1420bdc,c07c2d60,...) at kdb_enter+0x30
> > panic(c0746e47,c073180d,c0732bb2,c0764c8e,176,...) at panic+0x135
> > witness_checkorder(c082f0fc,1,c0764c8e,176,c55c0980,...) at 
> > witness_checkorder+0xd6
> > _sx_slock(c082f0fc,c0764c8e,176,c1420c64,c06f7e65,...) at _sx_slock+0x5f
> > msi_map(100,c1420d08,c1420d04,c1420c94,c04b5cc5,...) at msi_map+0x22
> > nexus_map_msi(c5552000,c55e4000,100,c1420d08,c1420d04,...) at 
> > nexus_map_msi+0x1f
> > pcib_map_msi(c55d9080,c55e4000,100,c1420d08,c1420d04,...) at 
> > pcib_map_msi+0x86
> > pcib_map_msi(c55e4200,c55e4000,100,c1420d08,c1420d04,...) at 
> > pcib_map_msi+0x86
> > pci_remap_msi_irq(c55e4000,100,c06ecb73,c54fff78,100,...) at 
> > pci_remap_msi_irq+0xeb
> > msi_assign_cpu(c55e6240,0,100,c079d170,c1420d70,...) at 
msi_assign_cpu+0x68
> > intr_assign_next_cpu(c55e6240,0,c07631d3,1c7,c54f3a44,...) at 
> > intr_assign_next_cpu+0x23
> > intr_shuffle_irqs(0,141e000,141ec00,141e000,0,...) at 
> > intr_shuffle_irqs+0x5e
> > mi_startup() at mi_startup+0xa0
> > begin() at begin+0x2c
> 
> In this case the culprit is intr_table_lock spinlock I think.
> This can be fixed switching the msi lock to be a spinlock instead than a 
> sx lock.

Actually, I think the real fix is I need to better handle the locking for 
assigning interrupts to CPUs.

> However I wonder, it is right to let sleepable lock to arise a WITNESS 
> exception if the lock is acquired in a critical section?
> I can understand this is a simple way to detect if a spinlock has been 
> previously called, but this leads to the 'false positive' case in which 
> we can have something like:
> 
> critical_enter();
> sx_xlock(&lock1);
> etc.etc.

This is wrong because once you do critical_enter(), you are free to assume 
that you won't do a context switch until you critical_exit(), and sx_xlock() 
would violate that if it blocked on the lock.

-- 
John Baldwin