On Thursday, October 23, 2014 11:35:47 am Mateusz Guzik wrote: > Author: mjg > Date: Thu Oct 23 15:35:47 2014 > New Revision: 273549 > URL: https://svnweb.freebsd.org/changeset/base/273549 > > Log: > Avoid taking the lock in selfdfree when not needed. > > Modified: > head/sys/kern/sys_generic.c > > Modified: head/sys/kern/sys_generic.c > ============================================================================== > --- head/sys/kern/sys_generic.c Thu Oct 23 15:16:40 2014 > (r273548) > +++ head/sys/kern/sys_generic.c Thu Oct 23 15:35:47 2014 > (r273549) > @@ -1600,10 +1600,11 @@ static void > selfdfree(struct seltd *stp, struct selfd *sfp) > { > STAILQ_REMOVE(&stp->st_selq, sfp, selfd, sf_link); > - mtx_lock(sfp->sf_mtx); > - if (sfp->sf_si) > + if (sfp->sf_si != NULL) { > + mtx_lock(sfp->sf_mtx); > TAILQ_REMOVE(&sfp->sf_si->si_tdlist, sfp, sf_threads); > - mtx_unlock(sfp->sf_mtx); > + mtx_unlock(sfp->sf_mtx); > + } > uma_zfree(selfd_zone, sfp);
How do you ensure that the value you read for sf_si here is up to date? In particular, if a thread is selecting on multiple fds and one awakens it, another fd can invoke selwakeup() while the thread is in seltdclear(). In that case, you might see a stale value of sf_si and not realize it is cleared by the selwakeup() after you get the lock and you will invoke TAILQ_REMOVE an extra time. -- John Baldwin _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
