Messages in this thread | | | Subject | Re: [patch] bug in cpuid & msr on nosmp machine | From | Rusty Russell <> | Date | Thu, 20 May 2004 18:34:36 +1000 |
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On Thu, 2004-05-20 at 17:32, Andrew Morton wrote: > I think what you want here is > > if (!cpu_possible(cpu) || !cpu_online(cpu)) > return -ENXIO;
It works, but it's not really correct. cpu_possible() is correct, but cpu_online() might no longer be true by the time do_cpu_read() calls do_cpu_id().
One way would be to do lock_cpu_hotplug() in cpuid_open() and introduce a cpuid_close() which would do unlock_cpu_hotplug(). Another would be to drop the check here, and fail the actual read. A final way is to do no checks, in which case it becomes a noop if the cpu is offline.
> --- 25/arch/i386/kernel/cpuid.c~cpuid-msr-range-checking-fix 2004-05-20 00:30:21.812166544 -0700 > +++ 25-akpm/arch/i386/kernel/cpuid.c 2004-05-20 00:31:16.607836336 -0700 > @@ -133,10 +133,12 @@ static ssize_t cpuid_read(struct file *f > static int cpuid_open(struct inode *inode, struct file *file) > { > int cpu = iminor(file->f_dentry->d_inode); > - struct cpuinfo_x86 *c = &(cpu_data)[cpu]; > + struct cpuinfo_x86 *c; > > - if (!cpu_online(cpu)) > + if (!cpu_possible(cpu) || !cpu_online(cpu)) > return -ENXIO; /* No such CPU */ > + > + c = &(cpu_data)[cpu]; > if (c->cpuid_level < 0) > return -EIO; /* CPUID not supported */ > > diff -puN arch/i386/kernel/msr.c~cpuid-msr-range-checking-fix arch/i386/kernel/msr.c > --- 25/arch/i386/kernel/msr.c~cpuid-msr-range-checking-fix 2004-05-20 00:30:21.836162896 -0700 > +++ 25-akpm/arch/i386/kernel/msr.c 2004-05-20 00:31:56.952702984 -0700 > @@ -239,10 +239,12 @@ static ssize_t msr_write(struct file * f > static int msr_open(struct inode *inode, struct file *file) > { > int cpu = iminor(file->f_dentry->d_inode); > - struct cpuinfo_x86 *c = &(cpu_data)[cpu]; > - > - if (!cpu_online(cpu)) > - return -ENXIO; /* No such CPU */ > + struct cpuinfo_x86 *c; > + > + if (!cpu_possible(cpu) || !cpu_online(cpu)) > + return -ENXIO; /* No such CPU */ > + > + c = &(cpu_data)[cpu]; > if ( !cpu_has(c, X86_FEATURE_MSR) ) > return -EIO; /* MSR not supported */ > > > _ -- Anyone who quotes me in their signature is an idiot -- Rusty Russell
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