Enable witness(4) blessings.
witness has long had a facility to "bless" designated lock pairs. Lock order reversals between a pair of blessed locks are not reported upon. We have a number of long-standing false positive LOR reports; start marking well-understood LORs as blessed. This change hides reports about UFS vnode locks and the UFS dirhash lock, and UFS vnode locks and buffer locks, since those are the two that I observe most often. In the long term it would be preferable to be able to limit blessings to a specific site where a lock is acquired, and/or extend witness to understand why some lock order reversals are valid (for example, if code paths with conflicting lock orders are serialized by a third lock), but in the meantime the false positives frequently confuse users and generate bug reports. Reviewed by: cem, kib, mckusick MFC after: 2 weeks Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D21039
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=350450
@ -132,9 +132,6 @@ __FBSDID("$FreeBSD$");
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#define LI_EXCLUSIVE 0x00010000 /* Exclusive lock instance. */
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#define LI_NORELEASE 0x00020000 /* Lock not allowed to be released. */
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/* Define this to check for blessed mutexes */
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#undef BLESSING
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#ifndef WITNESS_COUNT
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#define WITNESS_COUNT 1536
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#endif
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@ -278,12 +275,10 @@ struct witness_lock_order_hash {
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u_int wloh_count;
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};
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#ifdef BLESSING
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struct witness_blessed {
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const char *b_lock1;
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const char *b_lock2;
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};
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#endif
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struct witness_pendhelp {
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const char *wh_type;
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@ -318,9 +313,7 @@ witness_lock_order_key_equal(const struct witness_lock_order_key *a,
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static int _isitmyx(struct witness *w1, struct witness *w2, int rmask,
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const char *fname);
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static void adopt(struct witness *parent, struct witness *child);
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#ifdef BLESSING
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static int blessed(struct witness *, struct witness *);
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#endif
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static void depart(struct witness *w);
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static struct witness *enroll(const char *description,
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struct lock_class *lock_class);
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@ -726,14 +719,25 @@ static struct witness_order_list_entry order_lists[] = {
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{ NULL, NULL }
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};
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#ifdef BLESSING
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/*
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* Pairs of locks which have been blessed
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* Don't complain about order problems with blessed locks
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* Pairs of locks which have been blessed. Witness does not complain about
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* order problems with blessed lock pairs. Please do not add an entry to the
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* table without an explanatory comment.
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*/
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static struct witness_blessed blessed_list[] = {
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/*
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* See the comment in ufs_dirhash.c. Basically, a vnode lock serializes
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* both lock orders, so a deadlock cannot happen as a result of this
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* LOR.
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*/
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{ "dirhash", "bufwait" },
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/*
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* A UFS vnode may be locked in vget() while a buffer belonging to the
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* parent directory vnode is locked.
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*/
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{ "ufs", "bufwait" },
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};
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#endif
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/*
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* This global is set to 0 once it becomes safe to use the witness code.
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@ -1339,7 +1343,6 @@ witness_checkorder(struct lock_object *lock, int flags, const char *file,
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* We have a lock order violation, check to see if it
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* is allowed or has already been yelled about.
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*/
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#ifdef BLESSING
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/*
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* If the lock order is blessed, just bail. We don't
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@ -1348,7 +1351,6 @@ witness_checkorder(struct lock_object *lock, int flags, const char *file,
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*/
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if (blessed(w, w1))
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goto out;
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#endif
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/* Bail if this violation is known */
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if (w_rmatrix[w1->w_index][w->w_index] & WITNESS_REVERSAL)
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@ -2084,7 +2086,6 @@ isitmydescendant(struct witness *ancestor, struct witness *descendant)
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__func__));
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}
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#ifdef BLESSING
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static int
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blessed(struct witness *w1, struct witness *w2)
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{
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@ -2104,7 +2105,6 @@ blessed(struct witness *w1, struct witness *w2)
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}
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return (0);
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}
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#endif
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static struct witness *
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witness_get(void)
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