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Message-ID: <7ad25274-fa10-c5f1-44f4-fe7786169fa1@I-love.SAKURA.ne.jp>
Date: Tue, 12 Jul 2022 10:52:22 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
Arjan van de Ven <arjan@...ux.intel.com>
Cc: Greg KH <gregkh@...uxfoundation.org>,
"Rafael J. Wysocki" <rjw@...k.pl>,
Oliver Neukum <oneukum@...e.com>,
Wedson Almeida Filho <wedsonaf@...gle.com>,
Len Brown <len.brown@...el.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Linux PM <linux-pm@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] PM: hibernate: allow wait_for_device_probe() to
timeout when resuming from hibernation
On 2022/07/12 3:14, Rafael J. Wysocki wrote:
> On Mon, Jul 11, 2022 at 1:21 PM Tetsuo Handa
> <penguin-kernel@...ove.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?
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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