Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=baaca49f415b25fdbe2a8f3c22b39929e450fbfd
Commit:     baaca49f415b25fdbe2a8f3c22b39929e450fbfd
Parent:     6f7cc11aa6c7d5002e16096c7590944daece70ed
Author:     Gautham R Shenoy <[EMAIL PROTECTED]>
AuthorDate: Wed May 9 02:34:03 2007 -0700
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Wed May 9 12:30:51 2007 -0700

    Define and use new events,CPU_LOCK_ACQUIRE and CPU_LOCK_RELEASE
    
    This is an attempt to provide an alternate mechanism for postponing
    a hotplug event instead of using a global mechanism like lock_cpu_hotplug.
    
    The proposal is to add two new events namely CPU_LOCK_ACQUIRE and
    CPU_LOCK_RELEASE. The notification for these two events would be sent
    out before and after a cpu_hotplug event respectively.
    
    During the CPU_LOCK_ACQUIRE event, a cpu-hotplug-aware subsystem is
    supposed to acquire any per-subsystem hotcpu mutex ( Eg. workqueue_mutex
    in kernel/workqueue.c ).
    
    During the CPU_LOCK_RELEASE release event the cpu-hotplug-aware subsystem
    is supposed to release the per-subsystem hotcpu mutex.
    
    The reasons for defining new events as opposed to reusing the existing 
events
    like CPU_UP_PREPARE/CPU_UP_FAILED/CPU_ONLINE for locking/unlocking of
    per-subsystem hotcpu mutexes are as follow:
    
        - CPU_LOCK_ACQUIRE: All hotcpu mutexes are taken before subsystems
        start handling pre-hotplug events like CPU_UP_PREPARE/CPU_DOWN_PREPARE
        etc, thus ensuring a clean handling of these events.
    
        - CPU_LOCK_RELEASE: The hotcpu mutexes will be released only after
        all subsystems have handled post-hotplug events like CPU_DOWN_FAILED,
        CPU_DEAD,CPU_ONLINE etc thereby ensuring that there are no subsequent
        clashes amongst the interdependent subsystems after a cpu hotplugs.
    
    This patch also uses __raw_notifier_call chain in _cpu_up to take care
    of the dependency between the two consequetive calls to
    raw_notifier_call_chain.
    
    [EMAIL PROTECTED]: fix a bug]
    Signed-off-by: Gautham R Shenoy <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
 include/linux/notifier.h |    2 ++
 kernel/cpu.c             |   19 ++++++++++++++-----
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index e34221b..1903e54 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -194,6 +194,8 @@ extern int __srcu_notifier_call_chain(struct 
srcu_notifier_head *nh,
 #define CPU_DOWN_PREPARE       0x0005 /* CPU (unsigned)v going down */
 #define CPU_DOWN_FAILED                0x0006 /* CPU (unsigned)v NOT going 
down */
 #define CPU_DEAD               0x0007 /* CPU (unsigned)v dead */
+#define CPU_LOCK_ACQUIRE       0x0008 /* Acquire all hotcpu locks */
+#define CPU_LOCK_RELEASE       0x0009 /* Release all hotcpu locks */
 
 #endif /* __KERNEL__ */
 #endif /* _LINUX_NOTIFIER_H */
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 36e7084..4881049 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -132,12 +132,15 @@ static int _cpu_down(unsigned int cpu)
        if (!cpu_online(cpu))
                return -EINVAL;
 
+       raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE,
+                                               (void *)(long)cpu);
        err = raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
                                                (void *)(long)cpu);
        if (err == NOTIFY_BAD) {
                printk("%s: attempt to take down CPU %u failed\n",
                                __FUNCTION__, cpu);
-               return -EINVAL;
+               err = -EINVAL;
+               goto out_release;
        }
 
        /* Ensure that we are not runnable on dying cpu */
@@ -185,6 +188,9 @@ out_thread:
        err = kthread_stop(p);
 out_allowed:
        set_cpus_allowed(current, old_allowed);
+out_release:
+       raw_notifier_call_chain(&cpu_chain, CPU_LOCK_RELEASE,
+                                               (void *)(long)cpu);
        return err;
 }
 
@@ -206,13 +212,15 @@ int cpu_down(unsigned int cpu)
 /* Requires cpu_add_remove_lock to be held */
 static int __cpuinit _cpu_up(unsigned int cpu)
 {
-       int ret;
+       int ret, nr_calls = 0;
        void *hcpu = (void *)(long)cpu;
 
        if (cpu_online(cpu) || !cpu_present(cpu))
                return -EINVAL;
 
-       ret = raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
+       raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE, hcpu);
+       ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu,
+                                                       -1, &nr_calls);
        if (ret == NOTIFY_BAD) {
                printk("%s: attempt to bring up CPU %u failed\n",
                                __FUNCTION__, cpu);
@@ -233,8 +241,9 @@ static int __cpuinit _cpu_up(unsigned int cpu)
 
 out_notify:
        if (ret != 0)
-               raw_notifier_call_chain(&cpu_chain,
-                               CPU_UP_CANCELED, hcpu);
+               __raw_notifier_call_chain(&cpu_chain,
+                               CPU_UP_CANCELED, hcpu, nr_calls, NULL);
+       raw_notifier_call_chain(&cpu_chain, CPU_LOCK_RELEASE, hcpu);
 
        return ret;
 }
-
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