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SubjectRe: [PATCH v2 3/4] PM: hibernate: allow wait_for_device_probe() to timeout when resuming from hibernation
On Tue, Jul 12, 2022 at 3:52 AM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> On 2022/07/12 3:14, Rafael J. Wysocki wrote:
> > On Mon, Jul 11, 2022 at 1:21 PM Tetsuo Handa
> > <penguin-kernel@i-love.sakura.ne.jp> wrote:
> >>
> >> On 2022/07/11 17:12, Greg KH wrote:
> >>> creating a
> >>> locking loop like this should be resolved first,
> >>
> >> Rafael and Arjan, can we agree with removing wait_for_device_probe() from snapshot_open() ?
> >
> > No, we can't.
>
> Then, can we defer wait_for_device_probe() till first write()/ioctl()
> which is called without locks?

Yes, wait_for_device_probe() can be deferred to right before the first
actual access.

> kernel/power/user.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/power/user.c b/kernel/power/user.c
> index a00a728ddfc1..92aecb989c76 100644
> --- a/kernel/power/user.c
> +++ b/kernel/power/user.c
> @@ -26,6 +26,7 @@
>
> #include "power.h"
>
> +static bool need_wait;
>
> static struct snapshot_data {
> struct snapshot_handle handle;
> @@ -78,7 +79,7 @@ static int snapshot_open(struct inode *inode, struct file *filp)
> * Resuming. We may need to wait for the image device to
> * appear.
> */
> - wait_for_device_probe();
> + need_wait = true;
>
> data->swap = -1;
> data->mode = O_WRONLY;
> @@ -168,6 +169,11 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf,
> ssize_t res;
> loff_t pg_offp = *offp & ~PAGE_MASK;
>
> + if (need_wait) {
> + wait_for_device_probe();
> + need_wait = false;
> + }
> +
> lock_system_sleep();
>
> data = filp->private_data;
> @@ -244,6 +250,11 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
> loff_t size;
> sector_t offset;
>
> + if (need_wait) {
> + wait_for_device_probe();
> + need_wait = false;
> + }
> +
> if (_IOC_TYPE(cmd) != SNAPSHOT_IOC_MAGIC)
> return -ENOTTY;
> if (_IOC_NR(cmd) > SNAPSHOT_IOC_MAXNR)
> --
> 2.18.4

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