linux-kernel - Re: [PATCH v2 2/4] fs: allow all writers to be frozen

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <qqxbrigfucdh34lknahdre5cuovvzpqmmmn3cg7flpofj5jfbv@ly5t2sicegnj>
Date: Thu, 3 Apr 2025 16:59:59 +0200
From: Jan Kara <jack@...e.cz>
To: Christian Brauner <brauner@...nel.org>
Cc: linux-fsdevel@...r.kernel.org, jack@...e.cz, 
	Ard Biesheuvel <ardb@...nel.org>, linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org, 
	James Bottomley <James.Bottomley@...senpartnership.com>, mcgrof@...nel.org, 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: [PATCH v2 2/4] fs: allow all writers to be frozen

On Wed 02-04-25 16:07:32, Christian Brauner wrote:
> During freeze/thaw we need to be able to freeze all writers during
> suspend/hibernate. Otherwise tasks such as systemd-journald that mmap a
> file and write to it will not be frozen after we've already frozen the
> filesystem.
> 
> This has some risk of not being able to freeze processes in case a
> process has acquired SB_FREEZE_PAGEFAULT under mmap_sem or
> SB_FREEZE_INTERNAL under some other filesytem specific lock. If the
> filesystem is frozen, a task can block on the frozen filesystem with
> e.g., mmap_sem held. If some other task then blocks on grabbing that
> mmap_sem, hibernation ill fail because it is unable to hibernate a task
> holding mmap_sem. This could be fixed by making a range of filesystem
> related locks use freezable sleeping. That's impractical and not
> warranted just for suspend/hibernate. Assume that this is an infrequent
> problem and we've given userspace a way to skip filesystem freezing
> through a sysfs file.
> 
> Signed-off-by: Christian Brauner <brauner@...nel.org>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

BTW, I agree about the need to silence lockdep somehow.

								Honza

> ---
>  include/linux/fs.h | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index b379a46b5576..1edcba3cd68e 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1781,8 +1781,7 @@ static inline void __sb_end_write(struct super_block *sb, int level)
>  
>  static inline void __sb_start_write(struct super_block *sb, int level)
>  {
> -	percpu_down_read_freezable(sb->s_writers.rw_sem + level - 1,
> -				   level == SB_FREEZE_WRITE);
> +	percpu_down_read_freezable(sb->s_writers.rw_sem + level - 1, true);
>  }
>  
>  static inline bool __sb_start_write_trylock(struct super_block *sb, int level)
> 
> -- 
> 2.47.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR