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@suse.cz>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: stable@kernel.org

3 files changed, 30 insertions, 0 deletions

diff --git a/include/linux/freezer.h b/include/linux/freezer.h
index 0ab54e16a91f..d09af4b67cf1 100644
--- a/include/linux/freezer.h
+++ b/include/linux/freezer.h
@@ -39,6 +39,7 @@ extern bool __refrigerator(bool check_kthr_stop);
 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 check_kthr_stop) { return false; }
 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; }
 
diff --git a/kernel/power/process.c b/kernel/power/process.c
index 77274c9ba2f1..eeca00311f39 100644
--- a/kernel/power/process.c
+++ b/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");
+}
diff --git a/kernel/power/user.c b/kernel/power/user.c
index 6b1ab7a88522..e5a21a857302 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -274,6 +274,15 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
                 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: