Illumos 5981 - Deadlock in dmu_objset_find_dp
5981 Deadlock in dmu_objset_find_dp Reviewed by: Matthew Ahrens <mahrens@delphix.com> Reviewed by: Dan McDonald <danmcd@omniti.com> Approved by: Robert Mustacchi <rm@joyent.com> References: https://www.illumos.org/issues/5981 https://github.com/illumos/illumos-gate/commit/1d3f896 Ported-by: kernelOfTruth kerneloftruth@gmail.com Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #3553
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@ -156,6 +156,7 @@ void dsl_pool_mos_diduse_space(dsl_pool_t *dp,
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int64_t used, int64_t comp, int64_t uncomp);
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boolean_t dsl_pool_need_dirty_delay(dsl_pool_t *dp);
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void dsl_pool_config_enter(dsl_pool_t *dp, void *tag);
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void dsl_pool_config_enter_prio(dsl_pool_t *dp, void *tag);
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void dsl_pool_config_exit(dsl_pool_t *dp, void *tag);
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boolean_t dsl_pool_config_held(dsl_pool_t *dp);
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boolean_t dsl_pool_config_held_writer(dsl_pool_t *dp);
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@ -72,6 +72,7 @@ void rrw_init(rrwlock_t *rrl, boolean_t track_all);
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void rrw_destroy(rrwlock_t *rrl);
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void rrw_enter(rrwlock_t *rrl, krw_t rw, void *tag);
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void rrw_enter_read(rrwlock_t *rrl, void *tag);
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void rrw_enter_read_prio(rrwlock_t *rrl, void *tag);
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void rrw_enter_write(rrwlock_t *rrl);
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void rrw_exit(rrwlock_t *rrl, void *tag);
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boolean_t rrw_held(rrwlock_t *rrl, krw_t rw);
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@ -1784,7 +1784,15 @@ dmu_objset_find_dp_cb(void *arg)
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dmu_objset_find_ctx_t *dcp = arg;
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dsl_pool_t *dp = dcp->dc_dp;
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dsl_pool_config_enter(dp, FTAG);
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/*
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* We need to get a pool_config_lock here, as there are several
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* asssert(pool_config_held) down the stack. Getting a lock via
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* dsl_pool_config_enter is risky, as it might be stalled by a
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* pending writer. This would deadlock, as the write lock can
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* only be granted when our parent thread gives up the lock.
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* The _prio interface gives us priority over a pending writer.
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*/
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dsl_pool_config_enter_prio(dp, FTAG);
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dmu_objset_find_dp_impl(dcp);
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@ -1050,6 +1050,13 @@ dsl_pool_config_enter(dsl_pool_t *dp, void *tag)
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rrw_enter(&dp->dp_config_rwlock, RW_READER, tag);
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}
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void
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dsl_pool_config_enter_prio(dsl_pool_t *dp, void *tag)
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{
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ASSERT(!rrw_held(&dp->dp_config_rwlock, RW_READER));
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rrw_enter_read_prio(&dp->dp_config_rwlock, tag);
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}
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void
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dsl_pool_config_exit(dsl_pool_t *dp, void *tag)
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{
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@ -159,8 +159,8 @@ rrw_destroy(rrwlock_t *rrl)
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refcount_destroy(&rrl->rr_linked_rcount);
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}
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void
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rrw_enter_read(rrwlock_t *rrl, void *tag)
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static void
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rrw_enter_read_impl(rrwlock_t *rrl, boolean_t prio, void *tag)
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{
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mutex_enter(&rrl->rr_lock);
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#if !defined(DEBUG) && defined(_KERNEL)
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@ -176,7 +176,7 @@ rrw_enter_read(rrwlock_t *rrl, void *tag)
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ASSERT(refcount_count(&rrl->rr_anon_rcount) >= 0);
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while (rrl->rr_writer != NULL || (rrl->rr_writer_wanted &&
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refcount_is_zero(&rrl->rr_anon_rcount) &&
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refcount_is_zero(&rrl->rr_anon_rcount) && !prio &&
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rrn_find(rrl) == NULL))
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cv_wait(&rrl->rr_cv, &rrl->rr_lock);
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@ -191,6 +191,25 @@ rrw_enter_read(rrwlock_t *rrl, void *tag)
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mutex_exit(&rrl->rr_lock);
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}
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void
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rrw_enter_read(rrwlock_t *rrl, void *tag)
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{
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rrw_enter_read_impl(rrl, B_FALSE, tag);
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}
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/*
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* take a read lock even if there are pending write lock requests. if we want
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* to take a lock reentrantly, but from different threads (that have a
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* relationship to each other), the normal detection mechanism to overrule
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* the pending writer does not work, so we have to give an explicit hint here.
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*/
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void
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rrw_enter_read_prio(rrwlock_t *rrl, void *tag)
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{
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rrw_enter_read_impl(rrl, B_TRUE, tag);
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}
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void
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rrw_enter_write(rrwlock_t *rrl)
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{
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