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Message-Id: <200806221955.42597.david-b@pacbell.net>
Date: Sun, 22 Jun 2008 19:55:42 -0700
From: David Brownell <david-b@...bell.net>
To: lkml <linux-kernel@...r.kernel.org>
Cc: rtc-linux@...glegroups.com, Alan Cox <alan@...rguk.ukuu.org.uk>,
Jonathan Corbet <corbet@....net>
Subject: [PATCH] rtc: remove BKL for ioctl()
Remove implicit use of BKL in ioctl() from the RTC framework.
Instead, the rtc->ops_lock is used. That's the same lock that already
protects the RTC operations when they're issued through the exported
rtc_*() calls in drivers/rtc/interface.c ... making this a bugfix, not
just a cleanup, since both ioctl calls and set_alarm() need to update
IRQ enable flags and that implies a common lock (which RTC drivers as
a rule do not provide on their own).
A new comment at the declaration of "struct rtc_class_ops" summarizes
current locking rules. It's not clear to me that the exceptions listed
there should exist ... if not, those are pre-existing problems which can
be fixed in a patch that doesn't relate to BKL removal.
Signed-off-by: David Brownell <dbrownell@...rs.sourceforge.net>
---
presumably better than the quickie from Alan Cox
http://marc.info/?l=linux-kernel&m=121149082228913&w=2
drivers/rtc/rtc-dev.c | 58 ++++++++++++++++++++++++++++++++------------------
include/linux/rtc.h | 17 ++++++++++++++
2 files changed, 55 insertions(+), 20 deletions(-)
--- a/drivers/rtc/rtc-dev.c 2008-06-21 20:56:14.000000000 -0700
+++ b/drivers/rtc/rtc-dev.c 2008-06-21 21:46:14.000000000 -0700
@@ -203,7 +203,7 @@ static unsigned int rtc_dev_poll(struct
return (data != 0) ? (POLLIN | POLLRDNORM) : 0;
}
-static int rtc_dev_ioctl(struct inode *inode, struct file *file,
+static long rtc_dev_ioctl(struct file *file,
unsigned int cmd, unsigned long arg)
{
int err = 0;
@@ -213,6 +213,10 @@ static int rtc_dev_ioctl(struct inode *i
struct rtc_wkalrm alarm;
void __user *uarg = (void __user *) arg;
+ err = mutex_lock_interruptible(&rtc->ops_lock);
+ if (err)
+ return -EBUSY;
+
/* check that the calling task has appropriate permissions
* for certain ioctls. doing this check here is useful
* to avoid duplicate code in each driver.
@@ -221,26 +225,31 @@ static int rtc_dev_ioctl(struct inode *i
case RTC_EPOCH_SET:
case RTC_SET_TIME:
if (!capable(CAP_SYS_TIME))
- return -EACCES;
+ err = -EACCES;
break;
case RTC_IRQP_SET:
if (arg > rtc->max_user_freq && !capable(CAP_SYS_RESOURCE))
- return -EACCES;
+ err = -EACCES;
break;
case RTC_PIE_ON:
if (rtc->irq_freq > rtc->max_user_freq &&
!capable(CAP_SYS_RESOURCE))
- return -EACCES;
+ err = -EACCES;
break;
}
+ if (err)
+ goto done;
+
/* try the driver's ioctl interface */
if (ops->ioctl) {
err = ops->ioctl(rtc->dev.parent, cmd, arg);
- if (err != -ENOIOCTLCMD)
+ if (err != -ENOIOCTLCMD) {
+ mutex_unlock(&rtc->ops_lock);
return err;
+ }
}
/* if the driver does not provide the ioctl interface
@@ -259,15 +268,19 @@ static int rtc_dev_ioctl(struct inode *i
switch (cmd) {
case RTC_ALM_READ:
+ mutex_unlock(&rtc->ops_lock);
+
err = rtc_read_alarm(rtc, &alarm);
if (err < 0)
return err;
if (copy_to_user(uarg, &alarm.time, sizeof(tm)))
- return -EFAULT;
- break;
+ err = -EFAULT;
+ return err;
case RTC_ALM_SET:
+ mutex_unlock(&rtc->ops_lock);
+
if (copy_from_user(&alarm.time, uarg, sizeof(tm)))
return -EFAULT;
@@ -315,24 +328,26 @@ static int rtc_dev_ioctl(struct inode *i
}
}
- err = rtc_set_alarm(rtc, &alarm);
- break;
+ return rtc_set_alarm(rtc, &alarm);
case RTC_RD_TIME:
+ mutex_unlock(&rtc->ops_lock);
+
err = rtc_read_time(rtc, &tm);
if (err < 0)
return err;
if (copy_to_user(uarg, &tm, sizeof(tm)))
- return -EFAULT;
- break;
+ err = -EFAULT;
+ return err;
case RTC_SET_TIME:
+ mutex_unlock(&rtc->ops_lock);
+
if (copy_from_user(&tm, uarg, sizeof(tm)))
return -EFAULT;
- err = rtc_set_time(rtc, &tm);
- break;
+ return rtc_set_time(rtc, &tm);
case RTC_PIE_ON:
err = rtc_irq_set_state(rtc, NULL, 1);
@@ -370,34 +385,37 @@ static int rtc_dev_ioctl(struct inode *i
break;
#endif
case RTC_WKALM_SET:
+ mutex_unlock(&rtc->ops_lock);
if (copy_from_user(&alarm, uarg, sizeof(alarm)))
return -EFAULT;
- err = rtc_set_alarm(rtc, &alarm);
- break;
+ return rtc_set_alarm(rtc, &alarm);
case RTC_WKALM_RD:
+ mutex_unlock(&rtc->ops_lock);
err = rtc_read_alarm(rtc, &alarm);
if (err < 0)
return err;
if (copy_to_user(uarg, &alarm, sizeof(alarm)))
- return -EFAULT;
- break;
+ err = -EFAULT;
+ return err;
#ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
case RTC_UIE_OFF:
clear_uie(rtc);
- return 0;
+ break;
case RTC_UIE_ON:
- return set_uie(rtc);
+ err = set_uie(rtc);
#endif
default:
err = -ENOTTY;
break;
}
+done:
+ mutex_unlock(&rtc->ops_lock);
return err;
}
@@ -426,7 +444,7 @@ static const struct file_operations rtc_
.llseek = no_llseek,
.read = rtc_dev_read,
.poll = rtc_dev_poll,
- .ioctl = rtc_dev_ioctl,
+ .unlocked_ioctl = rtc_dev_ioctl,
.open = rtc_dev_open,
.release = rtc_dev_release,
.fasync = rtc_dev_fasync,
--- a/include/linux/rtc.h 2008-06-21 21:15:30.000000000 -0700
+++ b/include/linux/rtc.h 2008-06-21 21:42:59.000000000 -0700
@@ -115,6 +115,23 @@ extern void rtc_time_to_tm(unsigned long
extern struct class *rtc_class;
+/*
+ * For these RTC methods the device parameter is the physical device
+ * on whatever bus holds the hardware (I2C, Platform, SPI, etc), which
+ * was passed to rtc_device_register(). Its driver_data normally holds
+ * device state, including the rtc_device pointer for the RTC.
+ *
+ * Most of these methods are called with rtc_device.ops_lock held,
+ * through the rtc_*(struct rtc_device *, ...) calls.
+ *
+ * The (current) exceptions are mostly filesystem hooks:
+ * - the proc() hook for procfs
+ * - non-ioctl() chardev hooks: open(), release(), read_callback()
+ * - periodic irq calls: irq_set_state(), irq_set_freq()
+ *
+ * REVISIT those periodic irq calls *do* have ops_lock when they're
+ * issued through ioctl() ...
+ */
struct rtc_class_ops {
int (*open)(struct device *);
void (*release)(struct device *);
--
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