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linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, gost.dev@samsung.com Date: Wed, 26 Mar 2025 07:53:10 -0400 In-Reply-To: <20250326112220.1988619-4-mcgrof@kernel.org> References: <20250326112220.1988619-1-mcgrof@kernel.org> <20250326112220.1988619-4-mcgrof@kernel.org> Autocrypt: addr=James.Bottomley@HansenPartnership.com; prefer-encrypt=mutual; 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 8mT2Eh9SkH+YVOmaKsajgZgrBxA7fWmGoxXswEVxJIFj3vW7yNc0C5HaUdYa5iGOMs4kg2ht4s7yy7NRQuh7BifWjo6BQ6k4S1H+6axZucxhSV1L6zN9d+lr3Xo/vy1unzA== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2025-03-26 at 04:22 -0700, Luis Chamberlain wrote: > Add support to automatically handle freezing and thawing filesystems > during the kernel's suspend/resume cycle. >=20 > This is needed so that we properly really stop IO in flight without > races after userspace has been frozen. Without this we rely on > kthread freezing and its semantics are loose and error prone. > For instance, even though a kthread may use try_to_freeze() and end > up being frozen we have no way of being sure that everything that > has been spawned asynchronously from it (such as timers) have also > been stopped as well. >=20 > A long term advantage of also adding filesystem freeze / thawing > supporting during suspend / hibernation is that long term we may > be able to eventually drop the kernel's thread freezing completely > as it was originally added to stop disk IO in flight as we hibernate > or suspend. >=20 > This does not remove the superfluous freezer calls on all > filesystems. > Each filesystem must remove all the kthread freezer stuff and peg > the fs_type flags as supporting auto-freezing with the FS_AUTOFREEZE > flag. >=20 > Subsequent patches remove the kthread freezer usage from each > filesystem, one at a time to make all this work bisectable. > Once all filesystems remove the usage of the kthread freezer we > can remove the FS_AUTOFREEZE flag. >=20 > Reviewed-by: Jan Kara > Signed-off-by: Luis Chamberlain > --- > =C2=A0fs/super.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 | 50 > ++++++++++++++++++++++++++++++++++++++++++ > =C2=A0include/linux/fs.h=C2=A0=C2=A0=C2=A0=C2=A0 | 14 ++++++++++++ > =C2=A0kernel/power/process.c | 15 ++++++++++++- > =C2=A03 files changed, 78 insertions(+), 1 deletion(-) >=20 > diff --git a/fs/super.c b/fs/super.c > index 9995546cf159..7428f0b2251c 100644 > --- a/fs/super.c > +++ b/fs/super.c > @@ -2279,3 +2279,53 @@ int sb_init_dio_done_wq(struct super_block > *sb) > =C2=A0 return 0; > =C2=A0} > =C2=A0EXPORT_SYMBOL_GPL(sb_init_dio_done_wq); > + > +#ifdef CONFIG_PM_SLEEP > +static bool super_should_freeze(struct super_block *sb) > +{ > + if (!(sb->s_type->fs_flags & FS_AUTOFREEZE)) > + return false; > + /* > + * We don't freeze virtual filesystems, we skip those > filesystems with > + * no backing device. > + */ > + if (sb->s_bdi =3D=3D &noop_backing_dev_info) > + return false; This logic won't work for me because efivarfs is a pseudofilesystem and will have a noop bdi (or simply a null s_bdev, which is easier to check for). I was thinking of allowing freeze/thaw to continue for a s_bdev =3D=3D NULL filesystem if it provided a freeze or thaw callback, which will cover efivarfs. > + > + return true; > +} > + > +int fs_suspend_freeze_sb(struct super_block *sb, void *priv) > +{ > + int error =3D 0; > + > + if (!super_should_freeze(sb)) > + goto out; > + > + pr_info("%s (%s): freezing\n", sb->s_type->name, sb->s_id); > + > + error =3D freeze_super(sb, false); This is actually not wholly correct now. If the fs provides a sb- >freeze() method, you should use that instead of freeze_super() ... see how fs_bdev_freeze() is doing it. Additionally, the first thing freeze_super() does is take the superblock lock exclusively. Since you've already taken it exclusively in your iterate super, how does this not deadlock? You also need to handle the hibernate deadlock I ran into where a process (and some of the systemd processes are very fast at doing this) touches the filesystem and gets blocked on uninterruptible wait before the remainder of freeze_processes() runs. Once a task is uninterruptible hibernate fails. I came up with a simplistic solution: https://lore.kernel.org/linux-fsdevel/1af829aa7a65eb5ebc0614a00f7019615ed0f= 62b.camel@HansenPartnership.com/ But there should probably be a freezable percpu_rwsem that sb_write_started() can use to get these semantics rather than making every use of percpu_rwsem freezable. Regards, James