Re: [PATCH] x86_64: sync_tsc fix the race (so we can boot)

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• Reply: Eric W. Biederman: "Re: [PATCH] x86_64: sync_tsc fix the race (so we can boot)"
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Date:	Thu, 28 Jul 2005 10:35:41 -0700
To: "Eric W. Biederman" <ebiederm@xmission.com>

I have some problem with this patch.

YH

On 7/28/05, yhlu <yhlu.kernel@gmail.com> wrote:
> Do you mean solve the timing problem for 2 way dual core or 4 way
> single core above?
>
> YH
>
> On 7/27/05, Eric W. Biederman <ebiederm@xmission.com> wrote:
> >
> > sync_tsc was using smp_call_function to ask the boot processor
> > to report it's tsc value. smp_call_function performs an IPI_send_allbutself
> > which is a broadcast ipi. There is a window during processor startup during
> > which the target cpu has started and before it has initialized it's interrupt
> > vectors so it can properly process an interrupt. Receveing an interrupt
> > during that window will triple fault the cpu and do other nasty things.
> >
> > Why cli does not protect us from that is beyond me.
> >
> > The simple fix is to match ia64 and provide a smp_call_function_single.
> > Which avoids the broadcast and is more efficient.
> >
> > This certainly fixes the problem of getting stuck on boot which was
> > very easy to trigger on my SMP Hyperthreaded Xeon, and I think
> > it fixes it for the right reasons.
> >
> > I believe this patch suffers from apicid versus logical cpu number confusion.
> > I copied the basic logic from smp_send_reschedule and I can't find where
> > that translates from the logical cpuid to apicid. So it isn't quite
> > correct yet. It should be close enough that it shouldn't be too hard
> > to finish it up.
> >
> > More bug fixes after I have slept but I figured I needed to get this
> > one out for review.
> >
> > Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> >
> > ---
> >
> > arch/x86_64/kernel/smp.c | 65 ++++++++++++++++++++++++++++++++++++++++++
> > arch/x86_64/kernel/smpboot.c | 21 ++++++++------
> > include/asm-x86_64/smp.h | 2 +
> > 3 files changed, 79 insertions(+), 9 deletions(-)
> >
> > 571d8bdc5a935b85fb0ce5ff3fac9a59a86efe6e
> > diff --git a/arch/x86_64/kernel/smp.c b/arch/x86_64/kernel/smp.c
> > --- a/arch/x86_64/kernel/smp.c
> > +++ b/arch/x86_64/kernel/smp.c
> > @@ -294,6 +294,71 @@ void unlock_ipi_call_lock(void)
> > }
> >
> > /*
> > + * this function sends a 'generic call function' IPI to one other CPU
> > + * in the system.
> > + */
> > +static void __smp_call_function_single (int cpu, void (*func) (void *info), void *info,
> > + int nonatomic, int wait)
> > +{
> > + struct call_data_struct data;
> > + int cpus = 1;
> > +
> > + data.func = func;
> > + data.info = info;
> > + atomic_set(&data.started, 0);
> > + data.wait = wait;
> > + if (wait)
> > + atomic_set(&data.finished, 0);
> > +
> > + call_data = &data;
> > + wmb();
> > + /* Send a message to all other CPUs and wait for them to respond */
> > + send_IPI_mask(cpumask_of_cpu(cpu), CALL_FUNCTION_VECTOR);
> > +
> > + /* Wait for response */
> > + while (atomic_read(&data.started) != cpus)
> > + cpu_relax();
> > +
> > + if (!wait)
> > + return;
> > +
> > + while (atomic_read(&data.finished) != cpus)
> > + cpu_relax();
> > +}
> > +
> > +/*
> > + * Run a function on another CPU
> > + * <func> The function to run. This must be fast and non-blocking.
> > + * <info> An arbitrary pointer to pass to the function.
> > + * <nonatomic> Currently unused.
> > + * <wait> If true, wait until function has completed on other CPUs.
> > + * [RETURNS] 0 on success, else a negative status code.
> > + *
> > + * Does not return until the remote CPU is nearly ready to execute <func>
> > + * or is or has executed.
> > + */
> > +
> > +int smp_call_function_single (int cpu, void (*func) (void *info), void *info,
> > + int nonatomic, int wait)
> > +{
> > +
> > + int me = get_cpu(); /* prevent preemption and reschedule on another processor */
> > +
> > + if (cpu == me) {
> > + printk("%s: trying to call self\n", __func__);
> > + put_cpu();
> > + return -EBUSY;
> > + }
> > + spin_lock_bh(&call_lock);
> > +
> > + __smp_call_function_single(cpu, func,info,nonatomic,wait);
> > +
> > + spin_unlock_bh(&call_lock);
> > + put_cpu();
> > + return 0;
> > +}
> > +
> > +/*
> > * this function sends a 'generic call function' IPI to all other CPUs
> > * in the system.
> > */
> > diff --git a/arch/x86_64/kernel/smpboot.c b/arch/x86_64/kernel/smpboot.c
> > --- a/arch/x86_64/kernel/smpboot.c
> > +++ b/arch/x86_64/kernel/smpboot.c
> > @@ -229,9 +229,6 @@ static __cpuinit void sync_master(void *
> > {
> > unsigned long flags, i;
> >
> > - if (smp_processor_id() != boot_cpu_id)
> > - return;
> > -
> > go[MASTER] = 0;
> >
> > local_irq_save(flags);
> > @@ -280,7 +277,7 @@ get_delta(long *rt, long *master)
> > return tcenter - best_tm;
> > }
> >
> > -static __cpuinit void sync_tsc(void)
> > +static __cpuinit void sync_tsc(unsigned int master)
> > {
> > int i, done = 0;
> > long delta, adj, adjust_latency = 0;
> > @@ -294,9 +291,17 @@ static __cpuinit void sync_tsc(void)
> > } t[NUM_ROUNDS] __cpuinitdata;
> > #endif
> >
> > + printk(KERN_INFO "CPU %d: Syncing TSC to CPU %u.\n",
> > + smp_processor_id(), master);
> > +
> > go[MASTER] = 1;
> >
> > - smp_call_function(sync_master, NULL, 1, 0);
> > + /* It is dangerous to broadcast IPI as cpus are coming up,
> > + * as they may not be ready to accept them. So since
> > + * we only need to send the ipi to the boot cpu direct
> > + * the message, and avoid the race.
> > + */
> > + smp_call_function_single(master, sync_master, NULL, 1, 0);
> >
> > while (go[MASTER]) /* wait for master to be ready */
> > no_cpu_relax();
> > @@ -340,16 +345,14 @@ static __cpuinit void sync_tsc(void)
> > printk(KERN_INFO
> > "CPU %d: synchronized TSC with CPU %u (last diff %ld cycles, "
> > "maxerr %lu cycles)\n",
> > - smp_processor_id(), boot_cpu_id, delta, rt);
> > + smp_processor_id(), master, delta, rt);
> > }
> >
> > static void __cpuinit tsc_sync_wait(void)
> > {
> > if (notscsync || !cpu_has_tsc)
> > return;
> > - printk(KERN_INFO "CPU %d: Syncing TSC to CPU %u.\n", smp_processor_id(),
> > - boot_cpu_id);
> > - sync_tsc();
> > + sync_tsc(boot_cpu_id);
> > }
> >
> > static __init int notscsync_setup(char *s)
> > diff --git a/include/asm-x86_64/smp.h b/include/asm-x86_64/smp.h
> > --- a/include/asm-x86_64/smp.h
> > +++ b/include/asm-x86_64/smp.h
> > @@ -48,6 +48,8 @@ extern void unlock_ipi_call_lock(void);
> > extern int smp_num_siblings;
> > extern void smp_flush_tlb(void);
> > extern void smp_message_irq(int cpl, void *dev_id, struct pt_regs *regs);
> > +extern int smp_call_function_single (int cpuid, void (*func) (void *info), void *info,
> > + int retry, int wait);
> > extern void smp_send_reschedule(int cpu);
> > extern void smp_invalidate_rcv(void); /* Process an NMI */
> > extern void zap_low_mappings(void);
> > -
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• Previous message: Linus Torvalds: "Re: [PATCH] speed up on find_first_bit for i386 (let compiler do the work)"
• In reply to: yhlu: "Re: [PATCH] x86_64: sync_tsc fix the race (so we can boot)"
• Next in thread: Eric W. Biederman: "Re: [PATCH] x86_64: sync_tsc fix the race (so we can boot)"
• Reply: Eric W. Biederman: "Re: [PATCH] x86_64: sync_tsc fix the race (so we can boot)"
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