Subject: Re: raidstrategy() isn't interrupt-safe
To: Greg Oster <email@example.com>
From: Manuel Bouyer <firstname.lastname@example.org>
Date: 05/14/2005 23:54:11
On Sat, May 14, 2005 at 11:09:42AM -0600, Greg Oster wrote:
> Manuel Bouyer writes:
> > Hi,
> > a recent report on the port-xen list shows this stack trace:
> > panic: pool_get: rf_rad_pl: must have NOWAIT
> > Stopped at netbsd:cpu_Debugger+0x4 leave
> > cpu_Debugger(2ff,c9f31,2fe,401,c0657c4c) at netbsd:cpu_Debugger+0x4
> > panic(c05bb5c0,c0569d73,c0720d50,c04cc336,c09a6700) at netbsd:panic+0x121
> > pool_get(c0657c4c,2,c0e26000,10000,0) at netbsd:pool_get+0xf9
> > rf_AllocRaidAccDesc(c0aa2000,72,401,0,1) at netbsd:rf_AllocRaidAccDesc+0x30
> > rf_DoAccess(c0aa200,72,1,401,0) at netbsd:rf_DoAccess+0x40
> > raidstart(c0aa2000,c0b07000,0,0,1) at netbsd:raidstart+0x28f
> > raidstrategy(c0b07000,1,c0a4c118,c0acc800,c09d1084) at
> > netbsd:raidstrategy+0x136
> > ccdstart(c0a6d000,c09cd000,0,c0a4c118,c0a4c118) at netbsd:ccdstart+0x137
> > ccdstrategy(c09cd000,1,1,c09cd07c,0) at netbsd:ccdstrategy+0x142
> > xbdback_do_io(c09cd000,c09cd000,c0720dc0,c0212b42,c0a4c118) at
> > raidstrategy() ends up being called from interrupt context here,
> > and ends up calling pool_get(PR_WAITOK).
> > Quoting a previous post from Jason Thorpe on tech-kern:
> > > There are lots of other things that might cause a disk's strategy
> > > routine to be called from interrupt context (ccd / raidframe are good
> > > examples). Really, we need to audit ALL of the disk strategy
> > > routines and ensure that they are IPL_BIO interrupt-context safe.
> > so raidframe is broken in this respect. Should I fill a PR about this ?
> Please. If nothing else, as a placeholder/reminder.
> I'm not sure what a fix for this will look like.. it might require
> decoupling the "queuing bits" from the "doing bits" in raidstrategy().
> In any event, there is far too much stuff that gets done in
> raidstrategy() for it to be called from interrupt-land...
Doing something similar to what I've done in vnd ? Queue the buffers
in raidstrategy() to an alternate queue, and wake up a kernel thread to
handle the queue. It seems that this queue already exists, so it may not
be too hard to do. Maybe one of the existing kernel thread could be
used for that ?
Manuel Bouyer <email@example.com>
NetBSD: 26 ans d'experience feront toujours la difference