Date: Tue, 26 Jan 2010 08:10:25 +0100 From: Attilio Rao <attilio@freebsd.org> To: Rob Farmer <rfarmer@predatorlabs.net> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Marius Strobl <marius@freebsd.org> Subject: Re: svn commit: r202889 - head/sys/kern Message-ID: <3bbf2fe11001252310r408a6be4j9bc42618394b3e3d@mail.gmail.com> In-Reply-To: <b025ceb71001252225r56d4b0c8qe4c6affe338e6f9f@mail.gmail.com> References: <201001231554.o0NFsMbx049837@svn.freebsd.org> <b025ceb71001252225r56d4b0c8qe4c6affe338e6f9f@mail.gmail.com>
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2010/1/26 Rob Farmer <rfarmer@predatorlabs.net>: > On Sat, Jan 23, 2010 at 7:54 AM, Attilio Rao <attilio@freebsd.org> wrote: >> Author: attilio >> Date: Sat Jan 23 15:54:21 2010 >> New Revision: 202889 >> URL: http://svn.freebsd.org/changeset/base/202889 >> >> Log: >> =C2=A0- Fix a race in sched_switch() of sched_4bsd. >> =C2=A0 =C2=A0In the case of the thread being on a sleepqueue or a turnst= ile, the >> =C2=A0 =C2=A0sched_lock was acquired (without the aid of the td_lock int= erface) and >> =C2=A0 =C2=A0the td_lock was dropped. This was going to break locking ru= les on other >> =C2=A0 =C2=A0threads willing to access to the thread (via the td_lock in= terface) and >> =C2=A0 =C2=A0modify his flags (allowed as long as the container lock was= different >> =C2=A0 =C2=A0by the one used in sched_switch). >> =C2=A0 =C2=A0In order to prevent this situation, while sched_lock is acq= uired there >> =C2=A0 =C2=A0the td_lock gets blocked. [0] >> =C2=A0- Merge the ULE's internal function thread_block_switch() into the= global >> =C2=A0 =C2=A0thread_lock_block() and make the former semantic as the def= ault for >> =C2=A0 =C2=A0thread_lock_block(). This means that thread_lock_block() wi= ll not >> =C2=A0 =C2=A0disable interrupts when called (and consequently thread_unl= ock_block() >> =C2=A0 =C2=A0will not re-enabled them when called). This should be done = manually >> =C2=A0 =C2=A0when necessary. >> =C2=A0 =C2=A0Note, however, that ULE's thread_unblock_switch() is not re= aped >> =C2=A0 =C2=A0because it does reflect a difference in semantic due in ULE= (the >> =C2=A0 =C2=A0td_lock may not be necessarilly still blocked_lock when cal= ling this). >> =C2=A0 =C2=A0While asymmetric, it does describe a remarkable difference = in semantic >> =C2=A0 =C2=A0that is good to keep in mind. >> >> =C2=A0[0] Reported by: =C2=A0 =C2=A0 =C2=A0Kohji Okuno >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0<okuno dot kohji at jp dot panasonic dot com> >> =C2=A0Tested by: =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0Giovanni Trema= terra >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0<giovanni dot trematerra at gmail dot com> >> =C2=A0MFC: =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A02 weeks >> >> Modified: >> =C2=A0head/sys/kern/kern_mutex.c >> =C2=A0head/sys/kern/sched_4bsd.c >> =C2=A0head/sys/kern/sched_ule.c > > Hi, > > This commit seems to be causing me a kernel panic on sparc64 - details > are in PR 143215. Could you take a look before MFCing this? I think that the bug may be in cpu_switch() where the mutex parameter for sched_4bsd is not handled correctly. Does sparc64 support ULE? I don't think it does and I think that it simply ignores the third argument of cpu_switch() which is vital now for for sched_4bsd too (what needs to happen is to take the passed mutex and to set the TD_LOCK of old thread to be the third argument). Unluckilly, I can't do that in sparc64 asm right now, but it should not be too difficult to cope with it. Attilio --=20 Peace can only be achieved by understanding - A. Einstein
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