The patch titled Fix cpu hotplug problem in softirq code has been removed from the -mm tree. Its filename was fix-cpu-hotplug-problem-in-softirq-code.patch This patch was dropped because it was merged into mainline or a subsystem tree The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: Fix cpu hotplug problem in softirq code From: Christian Borntraeger <borntraeger@xxxxxxxxxx> currently cpu hotplug (unplug) seems broken on s390 and likely others. On cpu unplug the system starts to behave very strange and hangs. I bisected the problem to the following commit: commit 48f20a9a9488c432fc86df1ff4b7f4fa895d1183 Author: Olof Johansson <olof@xxxxxxxxx> Date: Tue Mar 4 15:23:25 2008 -0800 tasklets: execute tasklets in the same order they were queued Reverting this patch seems to fix the problem. I looked into takeover_tasklet and it seems that there is a way to corrupt the tail pointer of the current cpu. If the tasklet list of the frozen cpu is empty, the tail pointer of the current cpu points to the address of the head pointer of the stopped cpu and not to the next pointer of a tasklet_struct. This patch avoids the list splice of the list is empty and cpu hotplug seems to work as the tail pointer is not corrupted. Olof, can you look into that patch and ACK/NACK it so Andrew can push this to Linus, if appropriate? Please note that some lines are longer than 80 chars, but line-wrapping looked worse that this version. Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> Acked-by: Olof Johansson <olof@xxxxxxxxx> Acked-by: Ingo Molnar <mingo@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/softirq.c | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) diff -puN kernel/softirq.c~fix-cpu-hotplug-problem-in-softirq-code kernel/softirq.c --- a/kernel/softirq.c~fix-cpu-hotplug-problem-in-softirq-code +++ a/kernel/softirq.c @@ -589,16 +589,20 @@ static void takeover_tasklets(unsigned i local_irq_disable(); /* Find end, append list for that CPU. */ - *__get_cpu_var(tasklet_vec).tail = per_cpu(tasklet_vec, cpu).head; - __get_cpu_var(tasklet_vec).tail = per_cpu(tasklet_vec, cpu).tail; - per_cpu(tasklet_vec, cpu).head = NULL; - per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head; + if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) { + *(__get_cpu_var(tasklet_vec).tail) = per_cpu(tasklet_vec, cpu).head; + __get_cpu_var(tasklet_vec).tail = per_cpu(tasklet_vec, cpu).tail; + per_cpu(tasklet_vec, cpu).head = NULL; + per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head; + } raise_softirq_irqoff(TASKLET_SOFTIRQ); - *__get_cpu_var(tasklet_hi_vec).tail = per_cpu(tasklet_hi_vec, cpu).head; - __get_cpu_var(tasklet_hi_vec).tail = per_cpu(tasklet_hi_vec, cpu).tail; - per_cpu(tasklet_hi_vec, cpu).head = NULL; - per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head; + if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) { + *__get_cpu_var(tasklet_hi_vec).tail = per_cpu(tasklet_hi_vec, cpu).head; + __get_cpu_var(tasklet_hi_vec).tail = per_cpu(tasklet_hi_vec, cpu).tail; + per_cpu(tasklet_hi_vec, cpu).head = NULL; + per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head; + } raise_softirq_irqoff(HI_SOFTIRQ); local_irq_enable(); _ Patches currently in -mm which might be from borntraeger@xxxxxxxxxx are origin.patch git-kvm.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html