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Rework r276532 a bit. Always avoid recursing into the console drivers

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clients, hence they might not handle it very well. This change allows
debugging mutex problems with kernel console drivers when
"debug.witness.skipspin=0" is set in the boot environment.

MFC after:	1 week
This commit is contained in:
Hans Petter Selasky 2015-01-03 17:21:19 +00:00
parent f75ecd9b19
commit 04a8159ddf
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=276626
1 changed files with 8 additions and 7 deletions
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15
sys/kern/kern_cons.c
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@ -512,6 +512,13 @@ cnputs(char *p)
int unlock_reqd = 0;
if (use_cnputs_mtx) {
/*
* NOTE: Debug prints and/or witness printouts in
* console driver clients can cause the "cnputs_mtx"
* mutex to recurse. Simply return if that happens.
*/
if (mtx_owned(&cnputs_mtx))
return;
mtx_lock_spin(&cnputs_mtx);
unlock_reqd = 1;
}
@ -601,13 +608,7 @@ static void
cn_drvinit(void *unused)
{
/*
* NOTE: Debug prints and/or witness printouts in console
* driver clients can cause the "cnputs_mtx" mutex to
* recurse. Make sure the "MTX_RECURSE" flags is set!
*/
mtx_init(&cnputs_mtx, "cnputs_mtx", NULL, MTX_SPIN |
MTX_NOWITNESS | MTX_RECURSE);
mtx_init(&cnputs_mtx, "cnputs_mtx", NULL, MTX_SPIN | MTX_NOWITNESS);
use_cnputs_mtx = 1;
}