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| author | Dipankar Sarma <dipankar@in.ibm.com> | 2008-01-25 21:08:23 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-01-25 21:08:23 +0100 |
| commit | c2d727aa2ff17a1c8e5ed1e5e231bb8579b27e82 (patch) | |
| tree | 76b570288a72c1337920c5e60682316c554f00ee /kernel | |
| parent | c49443c538c1bbf50eda27e4a3711e9fc15176b0 (diff) | |
| download | lwn-c2d727aa2ff17a1c8e5ed1e5e231bb8579b27e82.tar.gz lwn-c2d727aa2ff17a1c8e5ed1e5e231bb8579b27e82.zip | |
Preempt-RCU: Use softirq instead of tasklets for
This patch makes RCU use softirq instead of tasklets.
It also adds a memory barrier after raising the softirq
inorder to ensure that the cpu sees the most recently updated
value of rcu->cur while processing callbacks.
The discussion of the related theoretical race pointed out
by James Huang can be found here --> http://lkml.org/lkml/2007/11/20/603
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Reviewed-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/rcupdate.c | 25 |
1 files changed, 17 insertions, 8 deletions
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index f2c1a04e9b18..4dfa0b792efa 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -73,8 +73,6 @@ static struct rcu_ctrlblk rcu_bh_ctrlblk = { DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L }; DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L }; -/* Fake initialization required by compiler */ -static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL}; static int blimit = 10; static int qhimark = 10000; static int qlowmark = 100; @@ -231,6 +229,18 @@ void rcu_barrier(void) } EXPORT_SYMBOL_GPL(rcu_barrier); +/* Raises the softirq for processing rcu_callbacks. */ +static inline void raise_rcu_softirq(void) +{ + raise_softirq(RCU_SOFTIRQ); + /* + * The smp_mb() here is required to ensure that this cpu's + * __rcu_process_callbacks() reads the most recently updated + * value of rcu->cur. + */ + smp_mb(); +} + /* * Invoke the completed RCU callbacks. They are expected to be in * a per-cpu list. @@ -260,7 +270,7 @@ static void rcu_do_batch(struct rcu_data *rdp) if (!rdp->donelist) rdp->donetail = &rdp->donelist; else - tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu)); + raise_rcu_softirq(); } /* @@ -412,7 +422,6 @@ static void rcu_offline_cpu(int cpu) &per_cpu(rcu_bh_data, cpu)); put_cpu_var(rcu_data); put_cpu_var(rcu_bh_data); - tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu); } #else @@ -424,7 +433,7 @@ static void rcu_offline_cpu(int cpu) #endif /* - * This does the RCU processing work from tasklet context. + * This does the RCU processing work from softirq context. */ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp, struct rcu_data *rdp) @@ -469,7 +478,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp, rcu_do_batch(rdp); } -static void rcu_process_callbacks(unsigned long unused) +static void rcu_process_callbacks(struct softirq_action *unused) { __rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data)); __rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data)); @@ -533,7 +542,7 @@ void rcu_check_callbacks(int cpu, int user) rcu_bh_qsctr_inc(cpu); } else if (!in_softirq()) rcu_bh_qsctr_inc(cpu); - tasklet_schedule(&per_cpu(rcu_tasklet, cpu)); + raise_rcu_softirq(); } static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp, @@ -556,7 +565,7 @@ static void __cpuinit rcu_online_cpu(int cpu) rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp); rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp); - tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL); + open_softirq(RCU_SOFTIRQ, rcu_process_callbacks, NULL); } static int __cpuinit rcu_cpu_notify(struct notifier_block *self, |