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Date: Sun, 29 Jan 2012 21:58:05 +0530
From: "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To: "Rafael J. Wysocki" <rjw@...k.pl>
CC: Linux PM list <linux-pm@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>, Jan Kara <jack@...e.cz>,
linux-fsdevel@...r.kernel.org, Dave Chinner <david@...morbit.com>,
Nigel Cunningham <nigel@...onice.net>,
Pavel Machek <pavel@....cz>, Martin@...htvoll.de
Subject: Re: [RFC][PATCH] PM / Sleep: Freeze filesystems during system suspend/hibernation
On 01/28/2012 07:15 PM, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@...k.pl>
>
> Freeze all filesystems during system suspend and (kernel-driven)
> hibernation by calling freeze_supers() for all superblocks and thaw
> them during the subsequent resume with the help of thaw_supers().
>
> This makes filesystems stay in a consistent state in case something
> goes wrong between system suspend (or hibernation) and the subsequent
> resume (e.g. journal replays won't be necessary in those cases). In
> particular, this should help to solve a long-standing issue that, in
> some cases, during resume from hibernation the boot loader causes the
> journal to be replied for the filesystem containing the kernel image
> and/or initrd causing it to become inconsistent with the information
> stored in the hibernation image.
>
> The user-space-driven hibernation (s2disk) is not covered by this
> change, because the freezing of filesystems prevents s2disk from
> accessing device special files it needs to do its job.
>
> This change is based on earlier work by Nigel Cunningham.
>
> Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> ---
> fs/super.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 3 +
> kernel/power/hibernate.c | 11 +++++--
> kernel/power/power.h | 23 --------------
> kernel/power/suspend.c | 42 +++++++++++++++++++++++++++
> 5 files changed, 128 insertions(+), 24 deletions(-)
>
...
> Index: linux/kernel/power/suspend.c
> ===================================================================
> --- linux.orig/kernel/power/suspend.c
> +++ linux/kernel/power/suspend.c
> @@ -29,6 +29,48 @@
>
> #include "power.h"
>
> +#ifdef CONFIG_SUSPEND_FREEZER
> +
> +static inline int suspend_freeze_processes(void)
> +{
> + int error;
> +
> + error = freeze_processes();
> + if (error)
> + return error;
> +
> + error = freeze_supers();
> + if (error) {
> + thaw_processes();
> + return error;
> + }
> +
> + error = freeze_kernel_threads();
> + if (error)
> + thaw_supers();
> +
If freezing of kernel threads fails, freeze_kernel_threads() calls
thaw_processes(), which means, even userspace processes get thawed.
So, there would be a time-window in which userspace is thawed but the
filesystems are still frozen. That is not very desirable right?
If that is right, then modifying freeze_kernel_threads() to call
thaw_kernel_threads() instead of thaw_processes() would fix it
(and of course, we would need to explicitly call thaw_processes
above).
BTW, after your patch posted at https://lkml.org/lkml/2012/1/27/501,
I very much wanted to write a patch to convert the semantics of
freeze/thaw to something like:
freeze_processes() calls thaw_processes on error.
//Both touch only userspace processes.
freeze_kernel_threads() calls thaw_kernel_threads() on error.
//Both touch only kernel threads.
Of course, such a patch would need to do a lot of fixing up at several
places, but IMHO, it would really help make the overall code more logical
and easier to understand.
I can write it up and post it soon, but then you'll have to rebase
your patch (this one) on top of that. What do you say?
Regards,
Srivatsa S. Bhat
> + return error;
> +}
> +
> +static inline void suspend_thaw_processes(void)
> +{
> + thaw_supers();
> + thaw_processes();
> +}
> +
> +#else /* !CONFIG_SUSPEND_FREEZER */
> +
> +static inline int suspend_freeze_processes(void)
> +{
> + return 0;
> +}
> +
> +static inline void suspend_thaw_processes(void)
> +{
> +}
> +
> +#endif /* !CONFIG_SUSPEND_FREEZER */
> +
> const char *const pm_states[PM_SUSPEND_MAX] = {
> [PM_SUSPEND_STANDBY] = "standby",
> [PM_SUSPEND_MEM] = "mem",
> Index: linux/kernel/power/hibernate.c
> ===================================================================
> --- linux.orig/kernel/power/hibernate.c
> +++ linux/kernel/power/hibernate.c
> @@ -626,12 +626,17 @@ int hibernate(void)
> if (error)
> goto Finish;
>
> - error = hibernation_snapshot(hibernation_mode == HIBERNATION_PLATFORM);
> + error = freeze_supers();
> if (error)
> goto Thaw;
> +
> + error = hibernation_snapshot(hibernation_mode == HIBERNATION_PLATFORM);
> + if (error)
> + goto Thaw_fs;
> +
> if (freezer_test_done) {
> freezer_test_done = false;
> - goto Thaw;
> + goto Thaw_fs;
> }
>
> if (in_suspend) {
> @@ -655,6 +660,8 @@ int hibernate(void)
> pr_debug("PM: Image restored successfully.\n");
> }
>
> + Thaw_fs:
> + thaw_supers();
> Thaw:
> thaw_processes();
> Finish:
>
--
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