svn commit: r284127 - head/sys/kern
Mark Johnston
markj at FreeBSD.org
Sun Jun 7 18:59:48 UTC 2015
Author: markj
Date: Sun Jun 7 18:59:47 2015
New Revision: 284127
URL: https://svnweb.freebsd.org/changeset/base/284127
Log:
witness: don't warn about matrix inconsistencies without holding the mutex
Lock order checking is done without the witness mutex held, so multiple
threads that are racing to establish a new lock order may read matrix
entries that are in an inconsistent state. Don't print a warning in this
case, but instead just redo the check after taking the witness lock.
Differential Revision: https://reviews.freebsd.org/D2713
Reviewed by: jhb
MFC after: 2 weeks
Sponsored by: EMC / Isilon Storage Division
Modified:
head/sys/kern/subr_witness.c
Modified: head/sys/kern/subr_witness.c
==============================================================================
--- head/sys/kern/subr_witness.c Sun Jun 7 15:54:57 2015 (r284126)
+++ head/sys/kern/subr_witness.c Sun Jun 7 18:59:47 2015 (r284127)
@@ -1170,19 +1170,25 @@ witness_checkorder(struct lock_object *l
/*
* Try to perform most checks without a lock. If this succeeds we
- * can skip acquiring the lock and return success.
+ * can skip acquiring the lock and return success. Otherwise we redo
+ * the check with the lock held to handle races with concurrent updates.
*/
w1 = plock->li_lock->lo_witness;
if (witness_lock_order_check(w1, w))
return;
+ mtx_lock_spin(&w_mtx);
+ if (witness_lock_order_check(w1, w)) {
+ mtx_unlock_spin(&w_mtx);
+ return;
+ }
+ witness_lock_order_add(w1, w);
+
/*
* Check for duplicate locks of the same type. Note that we only
* have to check for this on the last lock we just acquired. Any
* other cases will be caught as lock order violations.
*/
- mtx_lock_spin(&w_mtx);
- witness_lock_order_add(w1, w);
if (w1 == w) {
i = w->w_index;
if (!(lock->lo_flags & LO_DUPOK) && !(flags & LOP_DUPOK) &&
@@ -1996,7 +2002,10 @@ _isitmyx(struct witness *w1, struct witn
/* The flags on one better be the inverse of the flags on the other */
if (!((WITNESS_ATOD(r1) == r2 && WITNESS_DTOA(r2) == r1) ||
- (WITNESS_DTOA(r1) == r2 && WITNESS_ATOD(r2) == r1))) {
+ (WITNESS_DTOA(r1) == r2 && WITNESS_ATOD(r2) == r1))) {
+ /* Don't squawk if we're potentially racing with an update. */
+ if (!mtx_owned(&w_mtx))
+ return (0);
printf("%s: rmatrix mismatch between %s (index %d) and %s "
"(index %d): w_rmatrix[%d][%d] == %hhx but "
"w_rmatrix[%d][%d] == %hhx\n",
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