Date: Mon, 19 May 2025 22:33:58 -0400 From: Dennis Clarke <dclarke@blastwave.org> To: current@freebsd.org Subject: Just a question about sys/kern/subr_witness.c where witness_watch may be flipped to -1 Message-ID: <044f6767-01d2-40a5-a8fd-b5568658c9c0@blastwave.org>
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Just an odd message to see on the console :
# witness_lock_list_get: witness exhausted
Looking at https://cgit.freebsd.org/src/tree/sys/kern/subr_witness.c it
seems that the comment at line 370 is very clear :
/*
* If set to 0, lock order checking is disabled. If set to -1,
* witness is completely disabled. Otherwise witness performs full
* lock order checking for all locks. At runtime, lock order checking
* may be toggled. However, witness cannot be reenabled once it is
* completely disabled.
*/
static int witness_watch = 1;
So I wonder how I managed to get that message "witness exhausted" ?
At line 2203 I see :
static struct lock_list_entry *
witness_lock_list_get(void)
{
struct lock_list_entry *lle;
if (witness_watch == -1)
return (NULL);
mtx_lock_spin(&w_mtx);
lle = w_lock_list_free;
if (lle == NULL) {
witness_watch = -1;
mtx_unlock_spin(&w_mtx);
printf("%s: witness exhausted\n", __func__);
return (NULL);
}
w_lock_list_free = lle->ll_next;
mtx_unlock_spin(&w_mtx);
bzero(lle, sizeof(*lle));
return (lle);
}
Where it seems that indeed witness_watch has been flipped to -1 and that
functionality is now gone?
--
--
Dennis Clarke
RISC-V/SPARC/PPC/ARM/CISC
UNIX and Linux spoken
ps: the comment at line 43 is just plain silly.
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