On Fri, May 04, 2012 at 02:46:06AM -0400, Kirill A. Shutemov wrote:
> On Thu, May 03, 2012 at 10:41:22PM -0700, Guenter Roeck wrote:
> > On Thu, May 03, 2012 at 07:18:56AM -0400, Kirill A. Shutemov wrote:
> > > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> > >
> > > Let's rework code to allow arbitrary number of cores on a CPU, not
> > > limited by hardcoded array size.
> > >
> > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > > ---
> > > v2:
> > > - fix NULL pointer dereference. Thanks to R, Durgadoss;
> > > - use mutex instead of spinlock for list locking.
> > > ---
> > > drivers/hwmon/coretemp.c | 178 +++++++++++++++++++++++++++++++++-------------
> > > 1 files changed, 129 insertions(+), 49 deletions(-)
> > >
> > > diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
> > > index 54a70fe..1c66131 100644
> > > --- a/drivers/hwmon/coretemp.c
> > > +++ b/drivers/hwmon/coretemp.c
> > > @@ -36,6 +36,8 @@
> > > #include <linux/cpu.h>
> > > #include <linux/pci.h>
> > > #include <linux/smp.h>
> > > +#include <linux/list.h>
> > > +#include <linux/kref.h>
> > > #include <linux/moduleparam.h>
> > > #include <asm/msr.h>
> > > #include <asm/processor.h>
> > > @@ -52,11 +54,9 @@ module_param_named(tjmax, force_tjmax, int, 0444);
> > > MODULE_PARM_DESC(tjmax, "TjMax value in degrees Celsius");
> > >
> > > #define BASE_SYSFS_ATTR_NO 2 /* Sysfs Base attr no for coretemp */
> > > -#define NUM_REAL_CORES 16 /* Number of Real cores per cpu */
> > > #define CORETEMP_NAME_LENGTH 17 /* String Length of attrs */
> > > #define MAX_CORE_ATTRS 4 /* Maximum no of basic attrs */
> > > #define TOTAL_ATTRS (MAX_CORE_ATTRS + 1)
> > > -#define MAX_CORE_DATA (NUM_REAL_CORES + BASE_SYSFS_ATTR_NO)
> > >
> > > #define TO_PHYS_ID(cpu) (cpu_data(cpu).phys_proc_id)
> > > #define TO_CORE_ID(cpu) (cpu_data(cpu).cpu_core_id)
> > > @@ -82,6 +82,9 @@ MODULE_PARM_DESC(tjmax, "TjMax value in degrees Celsius");
> > > * @valid: If this is 1, the current temperature is valid.
> > > */
> > > struct temp_data {
> > > + struct list_head list;
> > > + struct kref refcount;
> >
> > Hi,
> >
> > the kref is not needed. The attribute access functions don't
> > need to be protected since the attributes for a core are deleted
> > before the core data itself is deleted. So it is not neccessary
> > to hold a lock while accessing/using temp_data in the attribute
> > access functions. All you need is to hold a mutex while you are
> > manipulating or walking the list.
>
> Without kref, what prevents following situation:
>
> CPU-A CPU-B
> tdata = get_temp_data();
> coretemp_remove_core() {
> device_remove_file();
> kfree(tdata);
> }
> <tdata dereference>
>
The remove function requires a semaphore which is held by the access function,
so device_remove_file() will only proceed after CPU-A is done with the sysfs access.
Guenter
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