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

Attilio Rao attilio at
Fri May 4 18:49:57 UTC 2007

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 @ 
> /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.

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:



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