Date: Sat, 22 Sep 2012 12:17:09 +0000 (UTC) From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r240813 - head/sys/kern Message-ID: <201209221217.q8MCH9Ip064471@svn.freebsd.org>
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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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