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    SubjectRe: [linux-pm] PM: cannot hibernate -- BUG at kernel/workqueue.c:3659
    On 01/28/2012 04:14 AM, Rafael J. Wysocki wrote:

    >> Rafael, thanks for the clarification in the other mail.
    >>
    >> Acked-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    >>
    >> 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@sisk.pl>
    > 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@suse.cz>
    > Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
    > Acked-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>


    Cc: stable@vger.kernel.org ?

    Other than that, the patch is perfect!

    Regards,
    Srivatsa S. Bhat

    > ---
    > 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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