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
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svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=284127
@ -1170,19 +1170,25 @@ witness_checkorder(struct lock_object *lock, int flags, const char *file,
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/*
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* Try to perform most checks without a lock. If this succeeds we
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* can skip acquiring the lock and return success.
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* can skip acquiring the lock and return success. Otherwise we redo
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* the check with the lock held to handle races with concurrent updates.
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*/
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w1 = plock->li_lock->lo_witness;
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if (witness_lock_order_check(w1, w))
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return;
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mtx_lock_spin(&w_mtx);
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if (witness_lock_order_check(w1, w)) {
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mtx_unlock_spin(&w_mtx);
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return;
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}
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witness_lock_order_add(w1, w);
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/*
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* Check for duplicate locks of the same type. Note that we only
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* have to check for this on the last lock we just acquired. Any
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* other cases will be caught as lock order violations.
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*/
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mtx_lock_spin(&w_mtx);
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witness_lock_order_add(w1, w);
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if (w1 == w) {
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i = w->w_index;
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if (!(lock->lo_flags & LO_DUPOK) && !(flags & LOP_DUPOK) &&
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@ -1996,7 +2002,10 @@ _isitmyx(struct witness *w1, struct witness *w2, int rmask, const char *fname)
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/* The flags on one better be the inverse of the flags on the other */
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if (!((WITNESS_ATOD(r1) == r2 && WITNESS_DTOA(r2) == r1) ||
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(WITNESS_DTOA(r1) == r2 && WITNESS_ATOD(r2) == r1))) {
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(WITNESS_DTOA(r1) == r2 && WITNESS_ATOD(r2) == r1))) {
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/* Don't squawk if we're potentially racing with an update. */
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if (!mtx_owned(&w_mtx))
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return (0);
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printf("%s: rmatrix mismatch between %s (index %d) and %s "
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"(index %d): w_rmatrix[%d][%d] == %hhx but "
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"w_rmatrix[%d][%d] == %hhx\n",
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