diff options
author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2009-09-23 09:50:41 -0700 |
---|---|---|
committer | Ingo Molnar <mingo@elte.hu> | 2009-09-23 19:46:29 +0200 |
commit | fc2219d49ef1606e7fd2c88af2b423b01ff3d319 (patch) | |
tree | 1c1cba7e4334898a98cf0e2c992e8cfef4b34979 /kernel/rcutree.c | |
parent | 0729e196147692d84d4c099fcff056eba2ed61d8 (diff) | |
download | kernel_samsung_smdk4412-fc2219d49ef1606e7fd2c88af2b423b01ff3d319.zip kernel_samsung_smdk4412-fc2219d49ef1606e7fd2c88af2b423b01ff3d319.tar.gz kernel_samsung_smdk4412-fc2219d49ef1606e7fd2c88af2b423b01ff3d319.tar.bz2 |
rcu: Clean up code based on review feedback from Josh Triplett
These issues identified during an old-fashioned face-to-face code
review extended over many hours.
o Bury various forms of the "rsp->completed == rsp->gpnum"
comparison into an rcu_gp_in_progress() function, which has
the beneficial side-effect of forcing consistent use of
ACCESS_ONCE().
o Replace hand-coded arithmetic with DIV_ROUND_UP().
o Bury several "!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x01])"
instances into an rcu_preempted_readers() function, as this
expression indicates that there are no readers blocked
within RCU read-side critical sections blocking the current
grace period. (Though there might well be similar readers
blocking the next grace period.)
o Remove a dangling rcu_restart_cpu() declaration that has
been dangling for almost 20 minor releases of the kernel.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12537246442687-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/rcutree.c')
-rw-r--r-- | kernel/rcutree.c | 29 |
1 files changed, 18 insertions, 11 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 52b06f6..f85b684 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -101,6 +101,16 @@ static void __cpuinit rcu_init_percpu_data(int cpu, struct rcu_state *rsp, #include "rcutree_plugin.h" /* + * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s + * permit this function to be invoked without holding the root rcu_node + * structure's ->lock, but of course results can be subject to change. + */ +static int rcu_gp_in_progress(struct rcu_state *rsp) +{ + return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum); +} + +/* * Note a quiescent state. Because we do not need to know * how many quiescent states passed, just if there was at least * one since the start of the grace period, this just sets a flag. @@ -173,9 +183,7 @@ cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp) static int cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp) { - /* ACCESS_ONCE() because we are accessing outside of lock. */ - return *rdp->nxttail[RCU_DONE_TAIL] && - ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum); + return *rdp->nxttail[RCU_DONE_TAIL] && !rcu_gp_in_progress(rsp); } /* @@ -482,7 +490,7 @@ static void print_other_cpu_stall(struct rcu_state *rsp) spin_lock_irqsave(&rnp->lock, flags); delta = jiffies - rsp->jiffies_stall; - if (delta < RCU_STALL_RAT_DELAY || rsp->gpnum == rsp->completed) { + if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) { spin_unlock_irqrestore(&rnp->lock, flags); return; } @@ -537,8 +545,7 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) /* We haven't checked in, so go dump stack. */ print_cpu_stall(rsp); - } else if (rsp->gpnum != rsp->completed && - delta >= RCU_STALL_RAT_DELAY) { + } else if (rcu_gp_in_progress(rsp) && delta >= RCU_STALL_RAT_DELAY) { /* They had two time units to dump stack, so complain. */ print_other_cpu_stall(rsp); @@ -703,9 +710,9 @@ rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp) * hold rnp->lock, as required by rcu_start_gp(), which will release it. */ static void cpu_quiet_msk_finish(struct rcu_state *rsp, unsigned long flags) - __releases(rnp->lock) + __releases(rcu_get_root(rsp)->lock) { - WARN_ON_ONCE(rsp->completed == rsp->gpnum); + WARN_ON_ONCE(!rcu_gp_in_progress(rsp)); rsp->completed = rsp->gpnum; rcu_process_gp_end(rsp, rsp->rda[smp_processor_id()]); rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */ @@ -1092,7 +1099,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) struct rcu_node *rnp = rcu_get_root(rsp); u8 signaled; - if (ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum)) + if (!rcu_gp_in_progress(rsp)) return; /* No grace period in progress, nothing to force. */ if (!spin_trylock_irqsave(&rsp->fqslock, flags)) { rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */ @@ -1251,7 +1258,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), rdp->nxttail[RCU_NEXT_TAIL] = &head->next; /* Start a new grace period if one not already started. */ - if (ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum)) { + if (!rcu_gp_in_progress(rsp)) { unsigned long nestflag; struct rcu_node *rnp_root = rcu_get_root(rsp); @@ -1331,7 +1338,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) } /* Has an RCU GP gone long enough to send resched IPIs &c? */ - if (ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum) && + if (rcu_gp_in_progress(rsp) && ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)) { rdp->n_rp_need_fqs++; return 1; |