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Date: Wed, 4 Jun 2008 00:20:05 +0200
From: Pavel Machek <pavel@...e.cz>
To: "Rafael J. Wysocki" <rjw@...k.pl>
Cc: Alan Cox <alan@...rguk.ukuu.org.uk>, linux-kernel@...r.kernel.org,
akpm@...l.org, pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [RFC][PATCH] snapshot: Use pm_mutex for mutual exclusion
Hi!
> Appended is what I think we can do.
Looks ok to me. ACK.
Pavel
> ---
> 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@...k.pl>
> ---
> kernel/power/user.c | 68 ++++++++++++++++++++++++++++++++--------------------
> 1 file changed, 42 insertions(+), 26 deletions(-)
>
> Index: linux-2.6/kernel/power/user.c
> ===================================================================
> --- linux-2.6.orig/kernel/power/user.c
> +++ linux-2.6/kernel/power/user.c
> @@ -70,16 +70,22 @@ static int snapshot_open(struct inode *i
> 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 *i
> 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
> 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
> else
> *offp = data->handle.offset;
> }
> +
> + Unlock:
> + mutex_unlock(&pm_mutex);
> +
> return res;
> }
>
> @@ -154,6 +171,8 @@ static ssize_t snapshot_write(struct fil
> 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 fil
> else
> *offp = data->handle.offset;
> }
> +
> + mutex_unlock(&pm_mutex);
> +
> return res;
> }
>
> @@ -180,16 +202,16 @@ static long snapshot_ioctl(struct file *
> 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 *
> 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 *
> 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 *
> 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 *
> error = -ENOTTY;
>
> }
> - unlock_kernel();
> +
> + mutex_unlock(&pm_mutex);
> +
> return error;
> }
>
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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