[PATCH tip/core/rcu 09/12] rcu: Push lock release to rcu_start_gp()'s callers
From: "Paul E. McKenney" If CPUs are to give prior notice of needed grace periods, it will be necessary to invoke rcu_start_gp() without dropping the root rcu_node structure's ->lock. This commit takes a second step in this direction by moving the release of this lock to rcu_start_gp()'s callers. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcutree.c| 24 ++-- kernel/rcutree_plugin.h |5 ++--- 2 files changed, 12 insertions(+), 17 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 2c6a931..0d53295 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1487,16 +1487,14 @@ static int __noreturn rcu_gp_kthread(void *arg) /* * Start a new RCU grace period if warranted, re-initializing the hierarchy * in preparation for detecting the next grace period. The caller must hold - * the root node's ->lock, which is released before return. Hard irqs must - * be disabled. + * the root node's ->lock and hard irqs must be disabled. * * Note that it is legal for a dying CPU (which is marked as offline) to * invoke this function. This can happen when the dying CPU reports its * quiescent state. */ static void -rcu_start_gp(struct rcu_state *rsp, unsigned long flags) - __releases(rcu_get_root(rsp)->lock) +rcu_start_gp(struct rcu_state *rsp) { struct rcu_data *rdp = this_cpu_ptr(rsp->rda); struct rcu_node *rnp = rcu_get_root(rsp); @@ -1510,15 +1508,13 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) */ rcu_advance_cbs(rsp, rnp, rdp); - if (!rsp->gp_kthread || - !cpu_needs_another_gp(rsp, rdp)) { + if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) { /* * Either we have not yet spawned the grace-period * task, this CPU does not need another grace period, * or a grace period is already in progress. * Either way, don't start a new grace period. */ - raw_spin_unlock_irqrestore(>lock, flags); return; } rsp->gp_flags = RCU_GP_FLAG_INIT; @@ -1528,15 +1524,14 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) /* Wake up rcu_gp_kthread() to start the grace period. */ wake_up(>gp_wq); - raw_spin_unlock_irqrestore(>lock, flags); } /* * Report a full set of quiescent states to the specified rcu_state * data structure. This involves cleaning up after the prior grace * period and letting rcu_start_gp() start up the next grace period - * if one is needed. Note that the caller must hold rnp->lock, as - * required by rcu_start_gp(), which will release it. + * if one is needed. Note that the caller must hold rnp->lock, which + * is released before return. */ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) __releases(rcu_get_root(rsp)->lock) @@ -2134,7 +2129,8 @@ __rcu_process_callbacks(struct rcu_state *rsp) local_irq_save(flags); if (cpu_needs_another_gp(rsp, rdp)) { raw_spin_lock(_get_root(rsp)->lock); /* irqs disabled. */ - rcu_start_gp(rsp, flags); /* releases above lock */ + rcu_start_gp(rsp); + raw_spin_unlock_irqrestore(_get_root(rsp)->lock, flags); } else { local_irq_restore(flags); } @@ -2214,11 +2210,11 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp, /* Start a new grace period if one not already started. */ if (!rcu_gp_in_progress(rsp)) { - unsigned long nestflag; struct rcu_node *rnp_root = rcu_get_root(rsp); - raw_spin_lock_irqsave(_root->lock, nestflag); - rcu_start_gp(rsp, nestflag); /* rlses rnp_root->lock */ + raw_spin_lock(_root->lock); + rcu_start_gp(rsp); + raw_spin_unlock(_root->lock); } else { /* Give the grace period a kick. */ rdp->blimit = LONG_MAX; diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index bcd8268..7a66312 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2220,7 +2220,6 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp) unsigned long c; bool d; unsigned long flags; - unsigned long flags1; struct rcu_node *rnp = rdp->mynode; struct rcu_node *rnp_root = rcu_get_root(rdp->rsp); @@ -2282,8 +2281,8 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp) c, rnp->level, rnp->grplo, rnp->grphi, "Startedroot"); - local_save_flags(flags1); -
[PATCH tip/core/rcu 09/12] rcu: Push lock release to rcu_start_gp()'s callers
From: Paul E. McKenney paul.mcken...@linaro.org If CPUs are to give prior notice of needed grace periods, it will be necessary to invoke rcu_start_gp() without dropping the root rcu_node structure's -lock. This commit takes a second step in this direction by moving the release of this lock to rcu_start_gp()'s callers. Signed-off-by: Paul E. McKenney paul.mcken...@linaro.org Signed-off-by: Paul E. McKenney paul...@linux.vnet.ibm.com --- kernel/rcutree.c| 24 ++-- kernel/rcutree_plugin.h |5 ++--- 2 files changed, 12 insertions(+), 17 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 2c6a931..0d53295 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1487,16 +1487,14 @@ static int __noreturn rcu_gp_kthread(void *arg) /* * Start a new RCU grace period if warranted, re-initializing the hierarchy * in preparation for detecting the next grace period. The caller must hold - * the root node's -lock, which is released before return. Hard irqs must - * be disabled. + * the root node's -lock and hard irqs must be disabled. * * Note that it is legal for a dying CPU (which is marked as offline) to * invoke this function. This can happen when the dying CPU reports its * quiescent state. */ static void -rcu_start_gp(struct rcu_state *rsp, unsigned long flags) - __releases(rcu_get_root(rsp)-lock) +rcu_start_gp(struct rcu_state *rsp) { struct rcu_data *rdp = this_cpu_ptr(rsp-rda); struct rcu_node *rnp = rcu_get_root(rsp); @@ -1510,15 +1508,13 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) */ rcu_advance_cbs(rsp, rnp, rdp); - if (!rsp-gp_kthread || - !cpu_needs_another_gp(rsp, rdp)) { + if (!rsp-gp_kthread || !cpu_needs_another_gp(rsp, rdp)) { /* * Either we have not yet spawned the grace-period * task, this CPU does not need another grace period, * or a grace period is already in progress. * Either way, don't start a new grace period. */ - raw_spin_unlock_irqrestore(rnp-lock, flags); return; } rsp-gp_flags = RCU_GP_FLAG_INIT; @@ -1528,15 +1524,14 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) /* Wake up rcu_gp_kthread() to start the grace period. */ wake_up(rsp-gp_wq); - raw_spin_unlock_irqrestore(rnp-lock, flags); } /* * Report a full set of quiescent states to the specified rcu_state * data structure. This involves cleaning up after the prior grace * period and letting rcu_start_gp() start up the next grace period - * if one is needed. Note that the caller must hold rnp-lock, as - * required by rcu_start_gp(), which will release it. + * if one is needed. Note that the caller must hold rnp-lock, which + * is released before return. */ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) __releases(rcu_get_root(rsp)-lock) @@ -2134,7 +2129,8 @@ __rcu_process_callbacks(struct rcu_state *rsp) local_irq_save(flags); if (cpu_needs_another_gp(rsp, rdp)) { raw_spin_lock(rcu_get_root(rsp)-lock); /* irqs disabled. */ - rcu_start_gp(rsp, flags); /* releases above lock */ + rcu_start_gp(rsp); + raw_spin_unlock_irqrestore(rcu_get_root(rsp)-lock, flags); } else { local_irq_restore(flags); } @@ -2214,11 +2210,11 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp, /* Start a new grace period if one not already started. */ if (!rcu_gp_in_progress(rsp)) { - unsigned long nestflag; struct rcu_node *rnp_root = rcu_get_root(rsp); - raw_spin_lock_irqsave(rnp_root-lock, nestflag); - rcu_start_gp(rsp, nestflag); /* rlses rnp_root-lock */ + raw_spin_lock(rnp_root-lock); + rcu_start_gp(rsp); + raw_spin_unlock(rnp_root-lock); } else { /* Give the grace period a kick. */ rdp-blimit = LONG_MAX; diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index bcd8268..7a66312 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2220,7 +2220,6 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp) unsigned long c; bool d; unsigned long flags; - unsigned long flags1; struct rcu_node *rnp = rdp-mynode; struct rcu_node *rnp_root = rcu_get_root(rdp-rsp); @@ -2282,8 +2281,8 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp) c, rnp-level, rnp-grplo, rnp-grphi,