2010/1/27 Marius Strobl <mar...@alchemy.franken.de>: > On Tue, Jan 26, 2010 at 08:10:25AM +0100, Attilio Rao wrote: >> 2010/1/26 Rob Farmer <rfar...@predatorlabs.net>: >> > On Sat, Jan 23, 2010 at 7:54 AM, Attilio Rao <atti...@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. >> > > The following patch adds handling of the mutex parameter to the > sparc64 cpu_switch(): > http://people.freebsd.org/~marius/sparc64_cpu_switch_mtx.diff > This patch works fine with r202888. With r202889 it allows the > machine to boot again, however putting some load on the machine > causes it to issue a reset without a chance to debug. I've also > tried with some variations like duplicating the old cpu_switch() > for cpu_throw() so the altered cpu_switch() doesn't need to > distinguish between the to cases and only assigning old->td_lock > right before return but nothing made a difference. Given that > this leaves little room for a bug in the cpu_switch() changes I > suspect r202889 also breaks additional assumptions. For example > the sparc64 pmap code used sched_lock, does that need to change > to be td_lock now maybe? Is there anything else that comes to > your mind in this regard?
Sorry for being lame with sparc64 assembly (so that I can't make much more productive help here), but the required patch, sched_4bsd only, should simply save the extra-argument of cpu_switch() (and cpu_throw() is not involved, so I'm not sure what is changing there) and move in TD_LOCK(%oldthreadreg) when it is safe to do (just after the oldthread switched out completely). It doesn't even require a memory barrier. This patch seems a bit too big and I wonder what else it does (or I'm entirely wrong and that's just what I asked here), maybe adding the ULE support as well? Said that, all the code, including MD parts should always use td_lock() and not doing explicit acquisitions/drops of sched_lock, if they want to support ULE (but probabilly even if they do not want), unless there is a big compelling reason (that I expect to be justified in comments at least). I'm not sure how to debug a possible reset or I'm not aware of further broken asserts, at least for tier-1 architectures. Thanks, Attilio -- Peace can only be achieved by understanding - A. Einstein _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"