Re: [PATCH v2 4/4] PM: hibernate: don't set PF_FREEZER_SKIP flag when manipulating /dev/snapshot
From: Rafael J. Wysocki
Date: Fri Jul 15 2022 - 13:47:20 EST
On Sun, Jul 10, 2022 at 4:26 AM Tetsuo Handa
<penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
>
> Since khungtaskd skips threads with PF_FREEZER_SKIP flag set, currently
> we can't report unbounded uninterruptible sleep when something went wrong
> while manipulating /dev/snapshot interface.
>
> Let's change snapshot_{open,read,write}() to use mutex_lock_killable()
> and change snapshot_release() to use mutex_lock(), so that khungtaskd can
> report unbounded uninterruptible sleep, by not setting PF_FREEZER_SKIP
> flag.
>
> Since /dev/snapshot is exclusive due to hibernate_acquire(), we could
> choose mutex_trylock() for snapshot_{open,read,write}() as with
> snapshot_ioctl(). But until we confirm that this patch does not
> break something, let's stay mutex_lock_killable().
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> Cc: Len Brown <len.brown@xxxxxxxxx>
> Cc: Pavel Machek <pavel@xxxxxx>
> ---
> This patch is only compile tested. Need to review if somewhere depends
> on PF_FREEZER_SKIP flag being set.
Yes, it does. The process operating the snapshot device cannot be
frozen, which is why it sets PF_FREEZER_SKIP in the first place.
>
> kernel/power/user.c | 19 +++++++++++--------
> 1 file changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/power/user.c b/kernel/power/user.c
> index 32dd5a855e8c..9936efa07022 100644
> --- a/kernel/power/user.c
> +++ b/kernel/power/user.c
> @@ -68,7 +68,8 @@ static int snapshot_open(struct inode *inode, struct file *filp)
> break;
> }
>
> - lock_system_sleep();
> + if (mutex_lock_killable(&system_transition_mutex))
> + return -EINTR;
>
> if (!hibernate_acquire()) {
> error = -EBUSY;
> @@ -102,7 +103,7 @@ static int snapshot_open(struct inode *inode, struct file *filp)
> data->dev = 0;
>
> Unlock:
> - unlock_system_sleep();
> + mutex_unlock(&system_transition_mutex);
>
> return error;
> }
> @@ -111,7 +112,7 @@ static int snapshot_release(struct inode *inode, struct file *filp)
> {
> struct snapshot_data *data;
>
> - lock_system_sleep();
> + mutex_lock(&system_transition_mutex);
>
> swsusp_free();
> data = filp->private_data;
> @@ -128,7 +129,7 @@ static int snapshot_release(struct inode *inode, struct file *filp)
> PM_POST_HIBERNATION : PM_POST_RESTORE);
> hibernate_release();
>
> - unlock_system_sleep();
> + mutex_unlock(&system_transition_mutex);
>
> return 0;
> }
> @@ -140,7 +141,8 @@ static ssize_t snapshot_read(struct file *filp, char __user *buf,
> ssize_t res;
> loff_t pg_offp = *offp & ~PAGE_MASK;
>
> - lock_system_sleep();
> + if (mutex_lock_killable(&system_transition_mutex))
> + return -EINTR;
>
> data = filp->private_data;
> if (!data->ready) {
> @@ -161,7 +163,7 @@ static ssize_t snapshot_read(struct file *filp, char __user *buf,
> *offp += res;
>
> Unlock:
> - unlock_system_sleep();
> + mutex_unlock(&system_transition_mutex);
>
> return res;
> }
> @@ -173,7 +175,8 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf,
> ssize_t res;
> loff_t pg_offp = *offp & ~PAGE_MASK;
>
> - lock_system_sleep();
> + if (mutex_lock_killable(&system_transition_mutex))
> + return -EINTR;
>
> data = filp->private_data;
>
> @@ -195,7 +198,7 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf,
> if (res > 0)
> *offp += res;
> unlock:
> - unlock_system_sleep();
> + mutex_unlock(&system_transition_mutex);
>
> return res;
> }
> --
> 2.18.4
>