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peterz@infradead.org, mingo@redhat.com, will@kernel.org, boqun.feng@gmail.com Date: Fri, 28 Mar 2025 10:21:03 -0400 In-Reply-To: References: <20250327140613.25178-1-James.Bottomley@HansenPartnership.com> <20250327140613.25178-5-James.Bottomley@HansenPartnership.com> 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-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2025-03-27 at 19:20 +0100, Jan Kara wrote: > On Thu 27-03-25 10:06:13, James Bottomley wrote: > > Introduce a freeze function, which iterates superblocks in reverse > > order freezing filesystems.=C2=A0 The indicator a filesystem is > > freezable is either possessing a s_bdev or a freeze_super method.=C2=A0 > > So this can be used in efivarfs, whether the freeze is for > > hibernate is also passed in via the new FREEZE_FOR_HIBERNATE flag. > >=20 > > 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. > >=20 > > Signed-off-by: James Bottomley > > >=20 > OK, I've seen you are setting the new FREEZE_FOR_HIBERNATE flag but I > didn't find anything using that flag. What do you plan to use it for? > Does you efivars usecase need it? I find passing down this detail > about the caller down to all filesystems a bit awkward. Isn't it > possible to extract the information "hibernate is ongoing" from PM > subsystem? That's right. I'm happy to post my patch below, but it depends on Al accepting the simple_next_child() proposal, so it doesn't apply to any tree. > > +/* > > + * 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; >=20 > Frankly, the global variable to propagate flags is pretty ugly... If > we really have to propagate some context into the iterator callback, > rather do it explicitly like iterate_supers() does it. Christian said the same thing. I can do it, but if you look in the power management subsystem, it relies on single threading and has a lot of global variables like this, so I thought of this as a simplification. > > +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 > > + =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 | FREEZE_HOLDER_KERNEL > > + =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 | freeze_flags); > > + else if (sb->s_bdev) > > + freeze_super(sb, FREEZE_MAY_NEST | > > FREEZE_HOLDER_KERNEL > > + =C2=A0=C2=A0=C2=A0=C2=A0 | freeze_flags); >=20 > Style nit - braces around above blocks would be IMHO appropriate. >=20 > > + 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); > > + pr_info("done."); > > +} >=20 > Generally this callback is not safe because it can race with > filesystem unmount and calling ->freeze_super() after the > filesystem's ->put_super() was called may have all sorts of > interesting effects (freeze_super() itself will just bail with a > warning, which is better but not great either). >=20 > The cleanest way I see how to make the iteration safe is to grab > active sb reference (like grab_super() does it) for the duration of > freeze_super() calls. Another possibility would be to grab sb- > >s_umount rwsem exclusively as Luis does it in his series but that > requires a bit of locking surgery and ->freeze_super() handlers make > this particularly nasty these days so I think active sb reference is > going to be nicer these days. Before getting into the how of this, could you just confirm my understanding of what the various locks do: https://lore.kernel.org/cd5c3d8aab9c5fb37fa018cb3302ecf7d2bdb140.camel@Hans= enPartnership.com Is correct? Regards, James