Re: [linux-pm] PM: cannot hibernate -- BUG at kernel/workqueue.c:3659

[Rafael J. Wysocki]

On Friday, January 27, 2012, Srivatsa S. Bhat wrote:
> On 01/26/2012 05:21 AM, Rafael J. Wysocki wrote:
> 
> > Jiri has already said that the patch works.
> > 
> > I think we could avoid the issue entirely by introducing thaw_kernel_threads
> > and making SNAPSHOT_FREE call it.  No other changes should be necessary.
> > 
> > IOW, Jiri, does the patch below help?
> > 
> > [BTW, the freeze_tasks()'s kerneldoc seems to be outdated.  Tejun?]
> > 
> > ---
> 
> 
> Rafael, thanks for the clarification in the other mail.
> 
> Acked-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
> 
> I think we need to get this into 3.2-stable as well, as Jiri mentioned.

Yes, we do.

Below it goes again with the missing comment in user.c and a changelog.

Please let me know if there's anything wrong with it, otherwise I'm going
to push it to Linus in a couple of days.

Thanks,
Rafael

---
From: Rafael J. Wysocki <rjw@xxxxxxx>
Subject: PM / Hibernate: Fix s2disk regression related to freezing workqueues

Commit 2aede851ddf08666f68ffc17be446420e9d2a056

  PM / Hibernate: Freeze kernel threads after preallocating memory

introduced a mechanism by which kernel threads were frozen after
the preallocation of hibernate image memory to avoid problems with
frozen kernel threads not responding to memory freeing requests.
However, it overlooked the s2disk code path in which the
SNAPSHOT_CREATE_IMAGE ioctl was run directly after SNAPSHOT_FREE,
which caused freeze_workqueues_begin() to BUG(), because it saw
that worqueues had been already frozen.

Although in principle this issue might be addressed by removing
the relevant BUG_ON() from freeze_workqueues_begin(), that would
reintroduce the very problem that commit 2aede851ddf08666f68ffc17be4
attempted to avoid into that particular code path.  For this reason,
to fix the issue at hand, introduce thaw_kernel_threads() and make
the SNAPSHOT_FREE ioctl execute it.

Special thanks to Srivatsa S. Bhat for detailed analysis of the
problem.

Reported-and-tested-by: Jiri Slaby <jslaby@xxxxxxx>
Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
Acked-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---
 include/linux/freezer.h |    2 ++
 kernel/power/process.c  |   19 +++++++++++++++++++
 kernel/power/user.c     |    9 +++++++++
 3 files changed, 30 insertions(+)

Index: linux/include/linux/freezer.h
===================================================================
--- linux.orig/include/linux/freezer.h
+++ linux/include/linux/freezer.h
@@ -39,6 +39,7 @@ extern bool __refrigerator(bool check_kt
 extern int freeze_processes(void);
 extern int freeze_kernel_threads(void);
 extern void thaw_processes(void);
+extern void thaw_kernel_threads(void);
 
 static inline bool try_to_freeze(void)
 {
@@ -174,6 +175,7 @@ static inline bool __refrigerator(bool c
 static inline int freeze_processes(void) { return -ENOSYS; }
 static inline int freeze_kernel_threads(void) { return -ENOSYS; }
 static inline void thaw_processes(void) {}
+static inline void thaw_kernel_threads(void) {}
 
 static inline bool try_to_freeze(void) { return false; }
 
Index: linux/kernel/power/process.c
===================================================================
--- linux.orig/kernel/power/process.c
+++ linux/kernel/power/process.c
@@ -188,3 +188,22 @@ void thaw_processes(void)
 	printk("done.\n");
 }
 
+void thaw_kernel_threads(void)
+{
+	struct task_struct *g, *p;
+
+	pm_nosig_freezing = false;
+	printk("Restarting kernel threads ... ");
+
+	thaw_workqueues();
+
+	read_lock(&tasklist_lock);
+	do_each_thread(g, p) {
+		if (p->flags & (PF_KTHREAD | PF_WQ_WORKER))
+			__thaw_task(p);
+	} while_each_thread(g, p);
+	read_unlock(&tasklist_lock);
+
+	schedule();
+	printk("done.\n");
+}
Index: linux/kernel/power/user.c
===================================================================
--- linux.orig/kernel/power/user.c
+++ linux/kernel/power/user.c
@@ -274,6 +274,15 @@ static long snapshot_ioctl(struct file *
 		swsusp_free();
 		memset(&data->handle, 0, sizeof(struct snapshot_handle));
 		data->ready = 0;
+		/*
+		 * It is necessary to thaw kernel threads here, because
+		 * SNAPSHOT_CREATE_IMAGE may be invoked directly after
+		 * SNAPSHOT_FREE.  In that case, if kernel threads were not
+		 * thawed, the preallocation of memory carried out by
+		 * hibernation_snapshot() might run into problems (i.e. it
+		 * might fail or even deadlock).
+		 */
+		thaw_kernel_threads();
 		break;
 
 	case SNAPSHOT_PREF_IMAGE_SIZE:
--
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