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Message-ID: <20240902132246.zorbw3filqh73dms@quack3>
Date: Mon, 2 Sep 2024 15:22:46 +0200
From: Jan Kara <jack@...e.cz>
To: Jeff Layton <jlayton@...nel.org>
Cc: Chuck Lever <chuck.lever@...cle.com>, Neil Brown <neilb@...e.de>,
Olga Kornievskaia <kolga@...app.com>, Dai Ngo <Dai.Ngo@...cle.com>,
Tom Talpey <tom@...pey.com>, Trond Myklebust <trondmy@...nel.org>,
Anna Schumaker <anna@...nel.org>,
Olga Kornievskaia <okorniev@...hat.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
Jonathan Corbet <corbet@....net>, Tom Haynes <loghyr@...il.com>,
linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 11/13] fs: handle delegated timestamps in
setattr_copy_mgtime
On Thu 29-08-24 09:26:49, Jeff Layton wrote:
> When updating the ctime on an inode for a SETATTR with a multigrain
> filesystem, we usually want to take the latest time we can get for the
> ctime. The exception to this rule is when there is a nfsd write
> delegation and the server is proxying timestamps from the client.
>
> When nfsd gets a CB_GETATTR response, we want to update the timestamp
> value in the inode to the values that the client is tracking. The client
> doesn't send a ctime value (since that's always determined by the
> exported filesystem), but it can send a mtime value. In the case where
> it does, then we may need to update the ctime to a value commensurate
> with that instead of the current time.
>
> If ATTR_DELEG is set, then use ia_ctime value instead of setting the
> timestamp to the current time.
>
> With the addition of delegated timestamps we can also receive a request
> to update only the atime, but we may not need to set the ctime. Trust
> the ATTR_CTIME flag in the update and only update the ctime when it's
> set.
>
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
Looks good to me. Feel free to add:
Reviewed-by: Jan Kara <jack@...e.cz>
Honza
> ---
> fs/attr.c | 28 +++++++++++++--------
> fs/inode.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 2 ++
> 3 files changed, 94 insertions(+), 10 deletions(-)
>
> diff --git a/fs/attr.c b/fs/attr.c
> index 3bcbc45708a3..392eb62aa609 100644
> --- a/fs/attr.c
> +++ b/fs/attr.c
> @@ -286,16 +286,20 @@ static void setattr_copy_mgtime(struct inode *inode, const struct iattr *attr)
> unsigned int ia_valid = attr->ia_valid;
> struct timespec64 now;
>
> - /*
> - * If the ctime isn't being updated then nothing else should be
> - * either.
> - */
> - if (!(ia_valid & ATTR_CTIME)) {
> - WARN_ON_ONCE(ia_valid & (ATTR_ATIME|ATTR_MTIME));
> - return;
> + if (ia_valid & ATTR_CTIME) {
> + /*
> + * In the case of an update for a write delegation, we must respect
> + * the value in ia_ctime and not use the current time.
> + */
> + if (ia_valid & ATTR_DELEG)
> + now = inode_set_ctime_deleg(inode, attr->ia_ctime);
> + else
> + now = inode_set_ctime_current(inode);
> + } else {
> + /* If ATTR_CTIME isn't set, then ATTR_MTIME shouldn't be either. */
> + WARN_ON_ONCE(ia_valid & ATTR_MTIME);
> }
>
> - now = inode_set_ctime_current(inode);
> if (ia_valid & ATTR_ATIME_SET)
> inode_set_atime_to_ts(inode, attr->ia_atime);
> else if (ia_valid & ATTR_ATIME)
> @@ -354,8 +358,12 @@ void setattr_copy(struct mnt_idmap *idmap, struct inode *inode,
> inode_set_atime_to_ts(inode, attr->ia_atime);
> if (ia_valid & ATTR_MTIME)
> inode_set_mtime_to_ts(inode, attr->ia_mtime);
> - if (ia_valid & ATTR_CTIME)
> - inode_set_ctime_to_ts(inode, attr->ia_ctime);
> + if (ia_valid & ATTR_CTIME) {
> + if (ia_valid & ATTR_DELEG)
> + inode_set_ctime_deleg(inode, attr->ia_ctime);
> + else
> + inode_set_ctime_to_ts(inode, attr->ia_ctime);
> + }
> }
> EXPORT_SYMBOL(setattr_copy);
>
> diff --git a/fs/inode.c b/fs/inode.c
> index 01f7df1973bd..f0fbfd470d8e 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -2835,6 +2835,80 @@ struct timespec64 inode_set_ctime_current(struct inode *inode)
> }
> EXPORT_SYMBOL(inode_set_ctime_current);
>
> +/**
> + * inode_set_ctime_deleg - try to update the ctime on a delegated inode
> + * @inode: inode to update
> + * @update: timespec64 to set the ctime
> + *
> + * Attempt to atomically update the ctime on behalf of a delegation holder.
> + *
> + * The nfs server can call back the holder of a delegation to get updated
> + * inode attributes, including the mtime. When updating the mtime we may
> + * need to update the ctime to a value at least equal to that.
> + *
> + * This can race with concurrent updates to the inode, in which
> + * case we just don't do the update.
> + *
> + * Note that this works even when multigrain timestamps are not enabled,
> + * so use it in either case.
> + */
> +struct timespec64 inode_set_ctime_deleg(struct inode *inode, struct timespec64 update)
> +{
> + ktime_t now, floor = atomic64_read(&ctime_floor);
> + struct timespec64 now_ts, cur_ts;
> + u32 cur, old;
> +
> + /* pairs with try_cmpxchg below */
> + cur = smp_load_acquire(&inode->i_ctime_nsec);
> + cur_ts.tv_nsec = cur & ~I_CTIME_QUERIED;
> + cur_ts.tv_sec = inode->i_ctime_sec;
> +
> + /* If the update is older than the existing value, skip it. */
> + if (timespec64_compare(&update, &cur_ts) <= 0)
> + return cur_ts;
> +
> + now = coarse_ctime(floor);
> + now_ts = ktime_to_timespec64(now);
> +
> + /* Clamp the update to "now" if it's in the future */
> + if (timespec64_compare(&update, &now_ts) > 0)
> + update = now_ts;
> +
> + update = timestamp_truncate(update, inode);
> +
> + /* No need to update if the values are already the same */
> + if (timespec64_equal(&update, &cur_ts))
> + return cur_ts;
> +
> + /*
> + * Try to swap the nsec value into place. If it fails, that means
> + * we raced with an update due to a write or similar activity. That
> + * stamp takes precedence, so just skip the update.
> + */
> +retry:
> + old = cur;
> + if (try_cmpxchg(&inode->i_ctime_nsec, &cur, update.tv_nsec)) {
> + inode->i_ctime_sec = update.tv_sec;
> + mgtime_counter_inc(mg_ctime_swaps);
> + return update;
> + }
> +
> + /*
> + * Was the change due to someone marking the old ctime QUERIED?
> + * If so then retry the swap. This can only happen once since
> + * the only way to clear I_CTIME_QUERIED is to stamp the inode
> + * with a new ctime.
> + */
> + if (!(old & I_CTIME_QUERIED) && (cur == (old | I_CTIME_QUERIED)))
> + goto retry;
> +
> + /* Otherwise, it was a new timestamp. */
> + cur_ts.tv_sec = inode->i_ctime_sec;
> + cur_ts.tv_nsec = cur & ~I_CTIME_QUERIED;
> + return cur_ts;
> +}
> +EXPORT_SYMBOL(inode_set_ctime_deleg);
> +
> /**
> * in_group_or_capable - check whether caller is CAP_FSETID privileged
> * @idmap: idmap of the mount @inode was found from
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index eff688e75f2f..ea7ed437d2b1 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1544,6 +1544,8 @@ static inline bool fsuidgid_has_mapping(struct super_block *sb,
>
> struct timespec64 current_time(struct inode *inode);
> struct timespec64 inode_set_ctime_current(struct inode *inode);
> +struct timespec64 inode_set_ctime_deleg(struct inode *inode,
> + struct timespec64 update);
>
> static inline time64_t inode_get_atime_sec(const struct inode *inode)
> {
>
> --
> 2.46.0
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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