From f528e7ba28492e363a64c80c414ded4cadf48f89 Mon Sep 17 00:00:00 2001 From: Tim Hockin Date: Sat, 21 Jul 2007 17:10:35 +0200 Subject: [PATCH] x86_64: O_EXCL on /dev/mcelog Background: /dev/mcelog is a clear-on-read interface. It is currently possible for multiple users to open and read() the device. Users are protected from each other during any one read, but not across reads. Description: This patch adds support for O_EXCL to /dev/mcelog. If a user opens the device with O_EXCL, no other user may open the device (EBUSY). Likewise, any user that tries to open the device with O_EXCL while another user has the device will fail (EBUSY). Result: Applications can get exclusive access to /dev/mcelog. Applications that do not care will be unchanged. Alternatives: A simpler choice would be to only allow one open() at all, regardless of O_EXCL. Testing: I wrote an application that opens /dev/mcelog with O_EXCL and observed that any other app that tried to open /dev/mcelog would fail until the exclusive app had closed the device. Caveats: None. Signed-off-by: Tim Hockin Signed-off-by: Andrew Morton Signed-off-by: Andi Kleen Signed-off-by: Linus Torvalds --- arch/x86_64/kernel/mce.c | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) diff --git a/arch/x86_64/kernel/mce.c b/arch/x86_64/kernel/mce.c index f3fb8174559..77fee481be4 100644 --- a/arch/x86_64/kernel/mce.c +++ b/arch/x86_64/kernel/mce.c @@ -465,6 +465,40 @@ void __cpuinit mcheck_init(struct cpuinfo_x86 *c) * Character device to read and clear the MCE log. */ +static DEFINE_SPINLOCK(mce_state_lock); +static int open_count; /* #times opened */ +static int open_exclu; /* already open exclusive? */ + +static int mce_open(struct inode *inode, struct file *file) +{ + spin_lock(&mce_state_lock); + + if (open_exclu || (open_count && (file->f_flags & O_EXCL))) { + spin_unlock(&mce_state_lock); + return -EBUSY; + } + + if (file->f_flags & O_EXCL) + open_exclu = 1; + open_count++; + + spin_unlock(&mce_state_lock); + + return 0; +} + +static int mce_release(struct inode *inode, struct file *file) +{ + spin_lock(&mce_state_lock); + + open_count--; + open_exclu = 0; + + spin_unlock(&mce_state_lock); + + return 0; +} + static void collect_tscs(void *data) { unsigned long *cpu_tsc = (unsigned long *)data; @@ -555,6 +589,8 @@ static int mce_ioctl(struct inode *i, struct file *f,unsigned int cmd, unsigned } static const struct file_operations mce_chrdev_ops = { + .open = mce_open, + .release = mce_release, .read = mce_read, .ioctl = mce_ioctl, }; -- 2.41.0