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Merge pull request #149 from linD026/master

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Fix potential concurrent problems in chardev2.c
This commit is contained in:
Jim Huang 2022-04-17 02:52:15 +08:00 committed by GitHub
commit 565a599342
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1 changed files with 10 additions and 9 deletions
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19
examples/chardev2.c
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@ -37,10 +37,6 @@ static int device_open(struct inode *inode, struct file *file)
{
pr_info("device_open(%p)\n", file);
/* We don't want to talk to two processes at the same time. */
if (atomic_cmpxchg(&already_open, CDEV_NOT_USED, CDEV_EXCLUSIVE_OPEN))
return -EBUSY;
try_module_get(THIS_MODULE);
return SUCCESS;
}
@ -49,9 +45,6 @@ static int device_release(struct inode *inode, struct file *file)
{
pr_info("device_release(%p,%p)\n", inode, file);
/* We're now ready for our next caller */
atomic_set(&already_open, CDEV_NOT_USED);
module_put(THIS_MODULE);
return SUCCESS;
}
@ -129,6 +122,11 @@ device_ioctl(struct file *file, /* ditto */
unsigned long ioctl_param)
{
int i;
long ret = SUCCESS;
/* We don't want to talk to two processes at the same time. */
if (atomic_cmpxchg(&already_open, CDEV_NOT_USED, CDEV_EXCLUSIVE_OPEN))
return -EBUSY;
/* Switch according to the ioctl called */
switch (ioctl_num) {
@ -166,11 +164,14 @@ device_ioctl(struct file *file, /* ditto */
/* This ioctl is both input (ioctl_param) and output (the return
* value of this function).
*/
return (long)message[ioctl_param];
ret = (long)message[ioctl_param];
break;
}
return SUCCESS;
/* We're now ready for our next caller */
atomic_set(&already_open, CDEV_NOT_USED);
return ret;
}
/* Module Declarations */