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;
}
tid_buffer[tid_tail++] = tid;
tid_tail %= TID_BUFFER_SIZE;
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