Messages in this thread Patch in this message | | | Subject | Re: [PATCH v12 15/17] counter: Implement events_queue_size sysfs attribute | From | Jarkko Nikula <> | Date | Tue, 6 Jul 2021 14:40:13 +0300 |
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Hi
On 7/5/21 11:19 AM, William Breathitt Gray wrote: > The events_queue_size sysfs attribute provides a way for users to > dynamically configure the Counter events queue size for the Counter > character device interface. The size is in number of struct > counter_event data structures. The number of elements will be rounded-up > to a power of 2 due to a requirement of the kfifo_alloc function called > during reallocation of the queue. > ... > diff --git a/drivers/counter/counter-chrdev.c b/drivers/counter/counter-chrdev.c > index 92805b1f65b8..13644c87d02a 100644 > --- a/drivers/counter/counter-chrdev.c > +++ b/drivers/counter/counter-chrdev.c > @@ -323,6 +323,9 @@ static int counter_chrdev_open(struct inode *inode, struct file *filp) > typeof(*counter), > chrdev); > > + if (!mutex_trylock(&counter->chrdev_lock)) > + return -EBUSY; > + > get_device(&counter->dev); > filp->private_data = counter; > > @@ -339,6 +342,7 @@ static int counter_chrdev_release(struct inode *inode, struct file *filp) > return err; > > put_device(&counter->dev); > + mutex_unlock(&counter->chrdev_lock); > > return 0; > }
I got two separate mutex warnings from counter_chrdev_open() by doing blind "cat /dev/counter0". First one due mutex being uninitialized:
[ 441.057342] DEBUG_LOCKS_WARN_ON(lock->magic != lock) [ 441.057355] WARNING: CPU: 2 PID: 366 at kernel/locking/mutex.c:1416 mutex_trylock+0xf2/0x130 ... [ 441.217331] Call Trace: [ 441.220062] counter_chrdev_open+0x21/0x60 [counter] ...
which I fixed trivially by (please be free to use it)
--- a/drivers/counter/counter-chrdev.c +++ b/drivers/counter/counter-chrdev.c @@ -364,6 +364,7 @@ int counter_chrdev_add(struct counter_device *const counter) spin_lock_init(&counter->events_list_lock); init_waitqueue_head(&counter->events_wait); mutex_init(&counter->events_lock); + mutex_init(&counter->chrdev_lock);
/* Initialize character device */ cdev_init(&counter->chrdev, &counter_fops); and after that
[ 16.564403] ================================================ [ 16.570725] WARNING: lock held when returning to user space! [ 16.577044] 5.13.0-next-20210706+ #4 Not tainted [ 16.582198] ------------------------------------------------ [ 16.588507] cat/331 is leaving the kernel with locks still held! [ 16.595214] 1 lock held by cat/331: [ 16.599103] #0: ffff888102bb3630 (&counter->chrdev_lock){+.+.}-{3:3}, at: counter_chrdev_open+0x21/0x60 [counter] Jarkko
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