From: kaf24@firebug.cl.cam.ac.uk Date: Mon, 12 Jun 2006 13:17:05 +0000 (+0100) Subject: [LINUX] Fix interaction between idle loop and RCU subsystem. X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~15972^2~8 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=b4bd6fd400a08d147288b2e3ee6322147464429a;p=xen.git [LINUX] Fix interaction between idle loop and RCU subsystem. There is a problem with the current implementation of stop_hz_timer in arch/i386/kernel/time-xen.c where the hz timer can be stopped on a CPU which has RCU callbacks pending. This patch backports a new RCU API created to fix this problem for the s390 implementation of stop_hz_timer and also updates the time-xen.c implementation of stop_hz_timer to call the new API. Signed-off-by: Harry Butterworth --- diff --git a/linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c b/linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c index 575596e3ee..fbc9f999ef 100644 --- a/linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c +++ b/linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c @@ -978,12 +978,19 @@ static void stop_hz_timer(void) unsigned int cpu = smp_processor_id(); unsigned long j; - /* We must do this /before/ checking rcu_pending(). */ cpu_set(cpu, nohz_cpu_mask); + + /* See matching smp_mb in rcu_start_batch in rcupdate.c. These mbs */ + /* ensure that if __rcu_pending (nested in rcu_needs_cpu) fetches a */ + /* value of rcp->cur that matches rdp->quiescbatch and allows us to */ + /* stop the hz timer then the cpumasks created for subsequent values */ + /* of cur in rcu_start_batch are guaranteed to pick up the updated */ + /* nohz_cpu_mask and so will not depend on this cpu. */ + smp_mb(); /* Leave ourselves in 'tick mode' if rcu or softirq pending. */ - if (rcu_pending(cpu) || local_softirq_pending()) { + if (rcu_needs_cpu(cpu) || local_softirq_pending()) { cpu_clear(cpu, nohz_cpu_mask); j = jiffies + 1; } else { diff --git a/patches/linux-2.6.16.13/rcu_needs_cpu.patch b/patches/linux-2.6.16.13/rcu_needs_cpu.patch new file mode 100644 index 0000000000..f2d60f7b02 --- /dev/null +++ b/patches/linux-2.6.16.13/rcu_needs_cpu.patch @@ -0,0 +1,33 @@ +--- ../pristine-linux-2.6.16.13/kernel/rcupdate.c 2006-05-02 22:38:44.000000000 +0100 ++++ ./kernel/rcupdate.c 2006-06-09 20:27:45.000000000 +0100 +@@ -485,6 +485,20 @@ int rcu_pending(int cpu) + __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu)); + } + ++/* ++ * Check to see if any future RCU-related work will need to be done ++ * by the current CPU, even if none need be done immediately, returning ++ * 1 if so. This function is part of the RCU implementation; it is -not- ++ * an exported member of the RCU API. ++ */ ++int rcu_needs_cpu(int cpu) ++{ ++ struct rcu_data *rdp = &per_cpu(rcu_data, cpu); ++ struct rcu_data *rdp_bh = &per_cpu(rcu_bh_data, cpu); ++ ++ return (!!rdp->curlist || !!rdp_bh->curlist || rcu_pending(cpu)); ++} ++ + void rcu_check_callbacks(int cpu, int user) + { + if (user || +--- ../pristine-linux-2.6.16.13/include/linux/rcupdate.h 2006-05-02 22:38:44.000000000 +0100 ++++ ./include/linux/rcupdate.h 2006-06-09 20:28:57.000000000 +0100 +@@ -134,6 +134,7 @@ static inline void rcu_bh_qsctr_inc(int + } + + extern int rcu_pending(int cpu); ++extern int rcu_needs_cpu(int cpu); + + /** + * rcu_read_lock - mark the beginning of an RCU read-side critical section.