From d6c304055b3cecd4ca865769ac7cea97a320727b Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 7 Oct 2009 21:43:22 +0200 Subject: [PATCH] x86, msr: Remove the bkl from msr_open() Remove the big kernel lock from msr_open() as it doesn't protect anything there. The only racy event that can happen here is a concurrent cpu shutdown. So let's look at what could be racy during/after the above event: - The cpu_online() check is racy, but the bkl doesn't help about that anyway it disables preemption but we may be chcking another cpu than the current one. Also the cpu can still become offlined between open and read calls. - The cpu_data(cpu) returns a safe pointer too. It won't be released on cpu offlining. But some fields can be changed from arch/x86/kernel/smpboot.c:remove_siblinginfo() : - phys_proc_id - cpu_core_id Those are not read from msr_open(). What we are checking is the x86_capability that is left untouched on offlining. So this removal looks safe. Signed-off-by: Frederic Weisbecker Cc: John Kacur Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Sven-Thorsten Dietrich LKML-Reference: <1254944602-7382-1-git-send-email-fweisbec@gmail.com> Signed-off-by: H. Peter Anvin --- arch/x86/kernel/msr.c | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-) diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c index 7dd950094178..c00610963238 100644 --- a/arch/x86/kernel/msr.c +++ b/arch/x86/kernel/msr.c @@ -174,21 +174,17 @@ static int msr_open(struct inode *inode, struct file *file) { unsigned int cpu = iminor(file->f_path.dentry->d_inode); struct cpuinfo_x86 *c = &cpu_data(cpu); - int ret = 0; - lock_kernel(); cpu = iminor(file->f_path.dentry->d_inode); - if (cpu >= nr_cpu_ids || !cpu_online(cpu)) { - ret = -ENXIO; /* No such CPU */ - goto out; - } + if (cpu >= nr_cpu_ids || !cpu_online(cpu)) + return -ENXIO; /* No such CPU */ + c = &cpu_data(cpu); if (!cpu_has(c, X86_FEATURE_MSR)) - ret = -EIO; /* MSR not supported */ -out: - unlock_kernel(); - return ret; + return -EIO; /* MSR not supported */ + + return 0; } /*