Date: Fri, 4 May 2007 15:46:50 -0400 From: John Baldwin <jhb@freebsd.org> To: attilio@freebsd.org Cc: freebsd-current@freebsd.org, Harald Schmalzbauer <h.schmalzbauer@omnisec.de> Subject: Re: PANIC: blockable slep lock (sx) msi @ ....msi.c:374 Message-ID: <200705041546.50690.jhb@freebsd.org> In-Reply-To: <463BF1A7.1050504@FreeBSD.org> References: <463B7A1D.6020602@omnisec.de> <463BF1A7.1050504@FreeBSD.org>
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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 @ > > /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
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