[PATCHv7 08/16] pps: make idr lock a mutex and protect idr_pre_get

Alexander Gordeev
2010-12-20T11:55:11Z

Now pps_idr_lock is never used in interrupt context so we can replace
spin_lock_irq/spin_unlock_irq with plain spin_lock/spin_unlock. But
there is also a potential race condition when someone can steal an id
which was allocated by idr_pre_get before it is used. So convert spin
lock to mutex and protect the whole id generation process.

Signed-off-by: Alexander Gordeev <lasaine@lvk.cs.msu.su>
---
drivers/pps/pps.c | 19 +++++++++++--------
1 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
index 79b4455..9e15cf1 100644
--- a/drivers/pps/pps.c
+++ b/drivers/pps/pps.c
@@ -27,6 +27,7 @@
#include <linux/sched.h>
#include <linux/uaccess.h>
#include <linux/idr.h>
+#include <linux/mutex.h>
#include <linux/cdev.h>
#include <linux/poll.h>
#include <linux/pps_kernel.h>
@@ -39,7 +40,7 @@
static dev_t pps_devt;
static struct class *pps_class;

-static DEFINE_SPINLOCK(pps_idr_lock);
+static DEFINE_MUTEX(pps_idr_lock);
static DEFINE_IDR(pps_idr);

/*
@@ -239,9 +240,9 @@ static void pps_device_destruct(struct device *dev)

/* release id here to protect others from using it while it's
* still in use */
- spin_lock_irq(&pps_idr_lock);
+ mutex_lock(&pps_idr_lock);
idr_remove(&pps_idr, pps->id);
- spin_unlock_irq(&pps_idr_lock);
+ mutex_unlock(&pps_idr_lock);

kfree(dev);
kfree(pps);
@@ -252,17 +253,19 @@ int pps_register_cdev(struct pps_device *pps)
int err;
dev_t devt;

+ mutex_lock(&pps_idr_lock);
/* Get new ID for the new PPS source */
- if (idr_pre_get(&pps_idr, GFP_KERNEL) == 0)
+ if (idr_pre_get(&pps_idr, GFP_KERNEL) == 0) {
+ mutex_unlock(&pps_idr_lock);
return -ENOMEM;
+ }

/* Now really allocate the PPS source.
* After idr_get_new() calling the new source will be freely available
* into the kernel.
*/
- spin_lock_irq(&pps_idr_lock);
err = idr_get_new(&pps_idr, pps, &pps->id);
- spin_unlock_irq(&pps_idr_lock);
+ mutex_unlock(&pps_idr_lock);

if (err < 0)
return err;
@@ -302,9 +305,9 @@ del_cdev:
cdev_del(&pps->cdev);

free_idr:
- spin_lock_irq(&pps_idr_lock);
+ mutex_lock(&pps_idr_lock);
idr_remove(&pps_idr, pps->id);
- spin_unlock_irq(&pps_idr_lock);
+ mutex_unlock(&pps_idr_lock);

return err;
}
--
1.7.2.3