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: >> - Fix a race in sched_switch() of sched_4bsd. >> In the case of the thread being on a sleepqueue or a turnstile, the >> sched_lock was acquired (without the aid of the td_lock interface) and >> the td_lock was dropped. This was going to break locking rules on other >> threads willing to access to the thread (via the td_lock interface) and >> modify his flags (allowed as long as the container lock was different >> by the one used in sched_switch). >> In order to prevent this situation, while sched_lock is acquired there >> the td_lock gets blocked. [0] >> - Merge the ULE's internal function thread_block_switch() into the global >> thread_lock_block() and make the former semantic as the default for >> thread_lock_block(). This means that thread_lock_block() will not >> disable interrupts when called (and consequently thread_unlock_block() >> will not re-enabled them when called). This should be done manually >> when necessary. >> Note, however, that ULE's thread_unblock_switch() is not reaped >> because it does reflect a difference in semantic due in ULE (the >> td_lock may not be necessarilly still blocked_lock when calling this). >> While asymmetric, it does describe a remarkable difference in semantic >> that is good to keep in mind. >> >> [0] Reported by: Kohji Okuno >> <okuno dot kohji at jp dot panasonic dot com> >> Tested by: Giovanni Trematerra >> <giovanni dot trematerra at gmail dot com> >> MFC: 2 weeks >> >> Modified: >> head/sys/kern/kern_mutex.c >> head/sys/kern/sched_4bsd.c >> head/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 -- Peace can only be achieved by understanding - A. Einstein
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