On Saturday, September 22, 2012 8:17:09 am Konstantin Belousov wrote: > Author: kib > Date: Sat Sep 22 12:17:09 2012 > New Revision: 240813 > URL: http://svn.freebsd.org/changeset/base/240813 > > Log: > Do not skip two elements of the tid_buffer when reusing the buffer > slot. This eventually results in exhaustion of the tid space, causing > new threads get tid -1 as identifier. > > The bad effect of having the thread id equal to -1 is that > UMTX_OP_UMUTEX_WAIT returns EFAULT for a lock owned by such thread, > because casuword cannot distinguish between literal value -1 read from > the address and -1 returned as an indication of faulted > access. _thr_umutex_lock() helper from libthr does not check for > errors from _umtx_op_err(2), causing an infinite loop in > mutex_lock_sleep(). > > We observed the JVM processes hanging and consuming enormous amount of > system time on machines with approximately 100 days uptime. > > Reported by: Mykola Dzham <freebsd levsha org ua> > MFC after: 1 week > > Modified: > head/sys/kern/kern_thread.c > > Modified: head/sys/kern/kern_thread.c > ============================================================================== > --- head/sys/kern/kern_thread.c Sat Sep 22 12:12:39 2012 > (r240812) > +++ head/sys/kern/kern_thread.c Sat Sep 22 12:17:09 2012 > (r240813) > @@ -116,7 +116,7 @@ tid_free(lwpid_t tid) > mtx_lock(&tid_lock); > if ((tid_tail + 1) % TID_BUFFER_SIZE == tid_head) { > tmp_tid = tid_buffer[tid_head++]; > - tid_head = (tid_head + 1) % TID_BUFFER_SIZE; > + tid_head %= TID_BUFFER_SIZE;
I actually think it would be clearer (to the reader) to remove the ++ side effect in the tmp_tid assignment so that the update to tid_head is self contained in one statement. Of course, the update to tid_tail below suffers from the same obfuscation. > } > tid_buffer[tid_tail++] = tid; > tid_tail %= TID_BUFFER_SIZE; > -- John Baldwin _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "[email protected]"
