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snapshot: Use pm_mutex for mutual exclusion

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We can avoid taking the BKL in snapshot_ioctl() if pm_mutex is used to prevent
the ioctls from being executed concurrently.

In addition, although it is only possible to open /dev/snapshot once, the task
which has done that may spawn a child that will inherit the open descriptor,
so in theory they can call snapshot_write(), snapshot_read() and
snapshot_release() concurrently.  pm_mutex can also be used for mutual
exclusion in such cases.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Len Brown <len.brown@intel.com>
This commit is contained in:
Rafael J. Wysocki 2008-06-11 22:09:45 +02:00 committed by Andi Kleen
parent 52d11025db
commit 25f2f3daad
1 changed files with 42 additions and 26 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

68
kernel/power/user.c
View File

@ -70,16 +70,22 @@ static int snapshot_open(struct inode *inode, struct file *filp)
struct snapshot_data *data;
int error;
if (!atomic_add_unless(&snapshot_device_available, -1, 0))
return -EBUSY;
mutex_lock(&pm_mutex);
if (!atomic_add_unless(&snapshot_device_available, -1, 0)) {
error = -EBUSY;
goto Unlock;
}
if ((filp->f_flags & O_ACCMODE) == O_RDWR) {
atomic_inc(&snapshot_device_available);
return -ENOSYS;
error = -ENOSYS;
goto Unlock;
}
if(create_basic_memory_bitmaps()) {
atomic_inc(&snapshot_device_available);
return -ENOMEM;
error = -ENOMEM;
goto Unlock;
}
nonseekable_open(inode, filp);
data = &snapshot_state;
@ -99,33 +105,36 @@ static int snapshot_open(struct inode *inode, struct file *filp)
if (error)
pm_notifier_call_chain(PM_POST_HIBERNATION);
}
if (error) {
if (error)
atomic_inc(&snapshot_device_available);
return error;
}
data->frozen = 0;
data->ready = 0;
data->platform_support = 0;
return 0;
Unlock:
mutex_unlock(&pm_mutex);
return error;
}
static int snapshot_release(struct inode *inode, struct file *filp)
{
struct snapshot_data *data;
mutex_lock(&pm_mutex);
swsusp_free();
free_basic_memory_bitmaps();
data = filp->private_data;
free_all_swap_pages(data->swap);
if (data->frozen) {
mutex_lock(&pm_mutex);
if (data->frozen)
thaw_processes();
mutex_unlock(&pm_mutex);
}
pm_notifier_call_chain(data->mode == O_WRONLY ?
PM_POST_HIBERNATION : PM_POST_RESTORE);
atomic_inc(&snapshot_device_available);
mutex_unlock(&pm_mutex);
return 0;
}
@ -135,9 +144,13 @@ static ssize_t snapshot_read(struct file *filp, char __user *buf,
struct snapshot_data *data;
ssize_t res;
mutex_lock(&pm_mutex);
data = filp->private_data;
if (!data->ready)
return -ENODATA;
if (!data->ready) {
res = -ENODATA;
goto Unlock;
}
res = snapshot_read_next(&data->handle, count);
if (res > 0) {
if (copy_to_user(buf, data_of(data->handle), res))
@ -145,6 +158,10 @@ static ssize_t snapshot_read(struct file *filp, char __user *buf,
else
*offp = data->handle.offset;
}
Unlock:
mutex_unlock(&pm_mutex);
return res;
}
@ -154,6 +171,8 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf,
struct snapshot_data *data;
ssize_t res;
mutex_lock(&pm_mutex);
data = filp->private_data;
res = snapshot_write_next(&data->handle, count);
if (res > 0) {
@ -162,6 +181,9 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf,
else
*offp = data->handle.offset;
}
mutex_unlock(&pm_mutex);
return res;
}
@ -180,16 +202,16 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
data = filp->private_data;
if (!mutex_trylock(&pm_mutex))
return -EBUSY;
lock_kernel();
data = filp->private_data;
switch (cmd) {
case SNAPSHOT_FREEZE:
if (data->frozen)
break;
mutex_lock(&pm_mutex);
printk("Syncing filesystems ... ");
sys_sync();
printk("done.\n");
@ -197,7 +219,6 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
error = freeze_processes();
if (error)
thaw_processes();
mutex_unlock(&pm_mutex);
if (!error)
data->frozen = 1;
break;
@ -205,9 +226,7 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
case SNAPSHOT_UNFREEZE:
if (!data->frozen || data->ready)
break;
mutex_lock(&pm_mutex);
thaw_processes();
mutex_unlock(&pm_mutex);
data->frozen = 0;
break;
@ -310,16 +329,11 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
error = -EPERM;
break;
}
if (!mutex_trylock(&pm_mutex)) {
error = -EBUSY;
break;
}
/*
* Tasks are frozen and the notifiers have been called with
* PM_HIBERNATION_PREPARE
*/
error = suspend_devices_and_enter(PM_SUSPEND_MEM);
mutex_unlock(&pm_mutex);
break;
case SNAPSHOT_PLATFORM_SUPPORT:
@ -392,7 +406,9 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
error = -ENOTTY;
}
unlock_kernel();
mutex_unlock(&pm_mutex);
return error;
}