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Message-ID: <20250328-ambulant-elektrisch-8127624ea520@brauner>
Date: Fri, 28 Mar 2025 13:01:14 +0100
From: Christian Brauner <brauner@...nel.org>
To: James Bottomley <James.Bottomley@...senpartnership.com>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
mcgrof@...nel.org, jack@...e.cz, hch@...radead.org, david@...morbit.com,
rafael@...nel.org, djwong@...nel.org, pavel@...nel.org, peterz@...radead.org,
mingo@...hat.com, will@...nel.org, boqun.feng@...il.com
Subject: Re: [RFC PATCH 4/4] vfs: add filesystem freeze/thaw callbacks for
power management
On Thu, Mar 27, 2025 at 10:06:13AM -0400, James Bottomley wrote:
> Introduce a freeze function, which iterates superblocks in reverse
> order freezing filesystems. The indicator a filesystem is freezable
> is either possessing a s_bdev or a freeze_super method. So this can
> be used in efivarfs, whether the freeze is for hibernate is also
> passed in via the new FREEZE_FOR_HIBERNATE flag.
>
> Thawing is done opposite to freezing (so superblock traversal in
> regular order) and the whole thing is plumbed into power management.
> The original ksys_sync() is preserved so the whole freezing step is
> optional (if it fails we're no worse off than we are today) so it
> doesn't inhibit suspend/hibernate if there's a failure.
>
> Signed-off-by: James Bottomley <James.Bottomley@...senPartnership.com>
> ---
> fs/super.c | 61 ++++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 5 ++++
> kernel/power/hibernate.c | 12 ++++++++
> kernel/power/suspend.c | 4 +++
> 4 files changed, 82 insertions(+)
>
> diff --git a/fs/super.c b/fs/super.c
> index 76785509d906..b4b0986414b0 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -1461,6 +1461,67 @@ static struct super_block *get_bdev_super(struct block_device *bdev)
> return sb;
> }
>
> +/*
> + * Kernel freezing and thawing is only done in the power management
> + * subsystem and is thus single threaded (so we don't have to worry
> + * here about multiple calls to filesystems_freeze/thaw().
> + */
> +
> +static int freeze_flags;
> +
> +static void filesystems_freeze_callback(struct super_block *sb)
> +{
> + /* errors don't fail suspend so ignore them */
> + if (sb->s_op->freeze_super)
> + sb->s_op->freeze_super(sb, FREEZE_MAY_NEST
> + | FREEZE_HOLDER_KERNEL
> + | freeze_flags);
> + else if (sb->s_bdev)
> + freeze_super(sb, FREEZE_MAY_NEST | FREEZE_HOLDER_KERNEL
> + | freeze_flags);
> + else {
> + pr_info("Ignoring filesystem %s\n", sb->s_type->name);
> + return;
> + }
> +
> + pr_info("frozen %s, now syncing block ...", sb->s_type->name);
> + sync_blockdev(sb->s_bdev);
Unnecessary, either the filesystem is responsible for this if it
provides its own ->freeze_super() or freeze_super() does it in
sync_filesystem.
> + pr_info("done.");
> +}
> +
> +/**
> + * filesystems_freeze - freeze callback for power management
> + *
> + * Freeze all active filesystems (in reverse superblock order)
> + */
> +void filesystems_freeze(bool for_hibernate)
> +{
> + freeze_flags = for_hibernate ? FREEZE_FOR_HIBERNATE : 0;
> + __iterate_supers_rev(filesystems_freeze_callback);
> +}
> +
> +static void filesystems_thaw_callback(struct super_block *sb)
> +{
> + if (sb->s_op->thaw_super)
> + sb->s_op->thaw_super(sb, FREEZE_MAY_NEST
> + | FREEZE_HOLDER_KERNEL
> + | freeze_flags);
> + else if (sb->s_bdev)
> + thaw_super(sb, FREEZE_MAY_NEST | FREEZE_HOLDER_KERNEL
> + | freeze_flags);
> +}
> +
> +/**
> + * filesystems_thaw - thaw callback for power management
> + *
> + * Thaw all active filesystems (in forward superblock order)
> + */
> +void filesystems_thaw(bool for_hibernate)
> +{
> + freeze_flags = for_hibernate ? FREEZE_FOR_HIBERNATE : 0;
> + __iterate_supers(filesystems_thaw_callback);
> +}
> +
> /**
> * fs_bdev_freeze - freeze owning filesystem of block device
> * @bdev: block device
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index cbbb704eff74..de154e9379ec 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2272,6 +2272,7 @@ extern loff_t vfs_dedupe_file_range_one(struct file *src_file, loff_t src_pos,
> * @FREEZE_HOLDER_KERNEL: kernel wants to freeze or thaw filesystem
> * @FREEZE_HOLDER_USERSPACE: userspace wants to freeze or thaw filesystem
> * @FREEZE_MAY_NEST: whether nesting freeze and thaw requests is allowed
> + * @FREEZE_FOR_HIBERNATE: set if freeze is from power management hibernate
> *
> * Indicate who the owner of the freeze or thaw request is and whether
> * the freeze needs to be exclusive or can nest.
> @@ -2285,6 +2286,7 @@ enum freeze_holder {
> FREEZE_HOLDER_KERNEL = (1U << 0),
> FREEZE_HOLDER_USERSPACE = (1U << 1),
> FREEZE_MAY_NEST = (1U << 2),
> + FREEZE_FOR_HIBERNATE = (1U << 3),
> };
>
> struct super_operations {
> @@ -3919,4 +3921,7 @@ static inline bool vfs_empty_path(int dfd, const char __user *path)
>
> int generic_atomic_write_valid(struct kiocb *iocb, struct iov_iter *iter);
>
> +void filesystems_freeze(bool for_hibernate);
> +void filesystems_thaw(bool for_hibernate);
> +
> #endif /* _LINUX_FS_H */
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index 10a01af63a80..fc2106e6685a 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -778,7 +778,12 @@ int hibernate(void)
>
> ksys_sync_helper();
>
> + pr_info("about to freeze filesystems\n");
> + filesystems_freeze(true);
> + pr_info("filesystem freeze done\n");
> +
> error = freeze_processes();
> + pr_info("process freeze done\n");
> if (error)
> goto Exit;
>
> @@ -788,7 +793,9 @@ int hibernate(void)
> if (error)
> goto Thaw;
>
> + pr_info("About to create snapshot\n");
> error = hibernation_snapshot(hibernation_mode == HIBERNATION_PLATFORM);
> + pr_info("snapshot done\n");
> if (error || freezer_test_done)
> goto Free_bitmaps;
>
> @@ -842,6 +849,8 @@ int hibernate(void)
> }
> thaw_processes();
>
> + filesystems_thaw(true);
> +
> /* Don't bother checking whether freezer_test_done is true */
> freezer_test_done = false;
> Exit:
> @@ -939,6 +948,8 @@ int hibernate_quiet_exec(int (*func)(void *data), void *data)
>
> thaw_processes();
>
> + filesystems_thaw(true);
> +
> exit:
> pm_notifier_call_chain(PM_POST_HIBERNATION);
>
> @@ -1041,6 +1052,7 @@ static int software_resume(void)
>
> error = load_image_and_restore();
> thaw_processes();
> + filesystems_thaw(true);
> Finish:
> pm_notifier_call_chain(PM_POST_RESTORE);
> Restore:
> diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
> index 09f8397bae15..34cc5b0c408c 100644
> --- a/kernel/power/suspend.c
> +++ b/kernel/power/suspend.c
> @@ -544,6 +544,7 @@ int suspend_devices_and_enter(suspend_state_t state)
> static void suspend_finish(void)
> {
> suspend_thaw_processes();
> + filesystems_thaw(false);
> pm_notifier_call_chain(PM_POST_SUSPEND);
> pm_restore_console();
> }
> @@ -581,6 +582,7 @@ static int enter_state(suspend_state_t state)
> trace_suspend_resume(TPS("sync_filesystems"), 0, true);
> ksys_sync_helper();
> trace_suspend_resume(TPS("sync_filesystems"), 0, false);
> + filesystems_freeze(false);
> }
>
> pm_pr_dbg("Preparing system for sleep (%s)\n", mem_sleep_labels[state]);
> @@ -603,6 +605,8 @@ static int enter_state(suspend_state_t state)
> pm_pr_dbg("Finishing wakeup.\n");
> suspend_finish();
> Unlock:
> + if (sync_on_suspend_enabled)
> + filesystems_thaw(false);
> mutex_unlock(&system_transition_mutex);
> return error;
> }
> --
> 2.43.0
>
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