From 3a9f84d354ce1e19956083c8e691727dea33bd5a Mon Sep 17 00:00:00 2001 From: Ed Swierk Date: Mon, 26 Jan 2009 15:33:31 -0800 Subject: [PATCH 1/3] signals, debug: fix BUG: using smp_processor_id() in preemptible code in print_fatal_signal() With print-fatal-signals=1 on a kernel with CONFIG_PREEMPT=y, sending an unexpected signal to a process causes a BUG: using smp_processor_id() in preemptible code. get_signal_to_deliver() releases the siglock before calling print_fatal_signal(), which calls show_regs(), which calls smp_processor_id(), which is not supposed to be called from a preemptible thread. Make sure show_regs() runs with preemption disabled. Signed-off-by: Ed Swierk Signed-off-by: Ingo Molnar --- kernel/signal.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/signal.c b/kernel/signal.c index e73759783dc8..b6b36768b758 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -909,7 +909,9 @@ static void print_fatal_signal(struct pt_regs *regs, int signr) } #endif printk("\n"); + preempt_disable(); show_regs(regs); + preempt_enable(); } static int __init setup_print_fatal_signals(char *str) From 4ab0a9409af5fad74ad1fc9e46d5a8b460f353e9 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Sat, 10 Jan 2009 21:58:09 -0800 Subject: [PATCH 2/3] cpumask: convert lib/smp_processor_id to new cpumask ops Impact: fix debug_smp_processor_id() for CONFIG_CPUMASK_OFFSTACK=y The scheduler now uses the new cpumask API, which deals up to nr_cpumask_bits, whereas the API used NR_CPUS bits. If CONFIG_CPUMASK_OFFSTACK=y these two are not equal, so the top bits are undefined. Leading to bug 12518 "BUG: using smp_processor_id() in preemptible [00000000] code: dellWirelessCtl/..." The fix is simple: use the modern API in the check. Signed-off-by: Rusty Russell Signed-off-by: Mike Travis Signed-off-by: Ingo Molnar --- lib/smp_processor_id.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c index 0f8fc22ed103..4689cb073da4 100644 --- a/lib/smp_processor_id.c +++ b/lib/smp_processor_id.c @@ -22,7 +22,7 @@ notrace unsigned int debug_smp_processor_id(void) * Kernel threads bound to a single CPU can safely use * smp_processor_id(): */ - if (cpus_equal(current->cpus_allowed, cpumask_of_cpu(this_cpu))) + if (cpumask_equal(¤t->cpus_allowed, cpumask_of(this_cpu))) goto out; /* From d7240b988017521ebf89edfadd42c0942f166850 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Thu, 29 Jan 2009 10:08:01 -0500 Subject: [PATCH 3/3] generic-ipi: use per cpu data for single cpu ipi calls The smp_call_function can be passed a wait parameter telling it to wait for all the functions running on other CPUs to complete before returning, or to return without waiting. Unfortunately, this is currently just a suggestion and not manditory. That is, the smp_call_function can decide not to return and wait instead. The reason for this is because it uses kmalloc to allocate storage to send to the called CPU and that CPU will free it when it is done. But if we fail to allocate the storage, the stack is used instead. This means we must wait for the called CPU to finish before continuing. Unfortunatly, some callers do no abide by this hint and act as if the non-wait option is mandatory. The MTRR code for instance will deadlock if the smp_call_function is set to wait. This is because the smp_call_function will wait for the other CPUs to finish their called functions, but those functions are waiting on the caller to continue. This patch changes the generic smp_call_function code to use per cpu variables if the allocation of the data fails for a single CPU call. The smp_call_function_many will fall back to the smp_call_function_single if it fails its alloc. The smp_call_function_single is modified to not force the wait state. Since we now are using a single data per cpu we must synchronize the callers to prevent a second caller modifying the data before the first called IPI functions complete. To do so, I added a flag to the call_single_data called CSD_FLAG_LOCK. When the single CPU is called (which can be called when a many call fails an alloc), we set the LOCK bit on this per cpu data. When the caller finishes it clears the LOCK bit. The caller must wait till the LOCK bit is cleared before setting it. When it is cleared, there is no IPI function using it. Signed-off-by: Steven Rostedt Signed-off-by: Peter Zijlstra Acked-by: Jens Axboe Acked-by: Linus Torvalds Signed-off-by: Ingo Molnar --- kernel/smp.c | 36 +++++++++++++++++++++++++++++++++--- 1 file changed, 33 insertions(+), 3 deletions(-) diff --git a/kernel/smp.c b/kernel/smp.c index 5cfa0e5e3e88..bbedbb7efe32 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -18,6 +18,7 @@ __cacheline_aligned_in_smp DEFINE_SPINLOCK(call_function_lock); enum { CSD_FLAG_WAIT = 0x01, CSD_FLAG_ALLOC = 0x02, + CSD_FLAG_LOCK = 0x04, }; struct call_function_data { @@ -186,6 +187,9 @@ void generic_smp_call_function_single_interrupt(void) if (data_flags & CSD_FLAG_WAIT) { smp_wmb(); data->flags &= ~CSD_FLAG_WAIT; + } else if (data_flags & CSD_FLAG_LOCK) { + smp_wmb(); + data->flags &= ~CSD_FLAG_LOCK; } else if (data_flags & CSD_FLAG_ALLOC) kfree(data); } @@ -196,6 +200,8 @@ void generic_smp_call_function_single_interrupt(void) } } +static DEFINE_PER_CPU(struct call_single_data, csd_data); + /* * smp_call_function_single - Run a function on a specific CPU * @func: The function to run. This must be fast and non-blocking. @@ -224,14 +230,38 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info, func(info); local_irq_restore(flags); } else if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) { - struct call_single_data *data = NULL; + struct call_single_data *data; if (!wait) { + /* + * We are calling a function on a single CPU + * and we are not going to wait for it to finish. + * We first try to allocate the data, but if we + * fail, we fall back to use a per cpu data to pass + * the information to that CPU. Since all callers + * of this code will use the same data, we must + * synchronize the callers to prevent a new caller + * from corrupting the data before the callee + * can access it. + * + * The CSD_FLAG_LOCK is used to let us know when + * the IPI handler is done with the data. + * The first caller will set it, and the callee + * will clear it. The next caller must wait for + * it to clear before we set it again. This + * will make sure the callee is done with the + * data before a new caller will use it. + */ data = kmalloc(sizeof(*data), GFP_ATOMIC); if (data) data->flags = CSD_FLAG_ALLOC; - } - if (!data) { + else { + data = &per_cpu(csd_data, me); + while (data->flags & CSD_FLAG_LOCK) + cpu_relax(); + data->flags = CSD_FLAG_LOCK; + } + } else { data = &d; data->flags = CSD_FLAG_WAIT; }