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
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=240813
@ -116,7 +116,7 @@ tid_free(lwpid_t tid)
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mtx_lock(&tid_lock);
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if ((tid_tail + 1) % TID_BUFFER_SIZE == tid_head) {
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tmp_tid = tid_buffer[tid_head++];
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tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
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tid_head %= TID_BUFFER_SIZE;
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}
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tid_buffer[tid_tail++] = tid;
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tid_tail %= TID_BUFFER_SIZE;
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