| Message ID | 20240715-mgtime-v6-1-48e5d34bd2ba@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | fs: multigrain timestamp redux | expand |
On Mon 15-07-24 08:48:52, Jeff Layton wrote: > The VFS has always used coarse-grained timestamps when updating the > ctime and mtime after a change. This has the benefit of allowing > filesystems to optimize away a lot metadata updates, down to around 1 > per jiffy, even when a file is under heavy writes. > > Unfortunately, this has always been an issue when we're exporting via > NFSv3, which relies on timestamps to validate caches. A lot of changes > can happen in a jiffy, so timestamps aren't sufficient to help the > client decide when to invalidate the cache. Even with NFSv4, a lot of > exported filesystems don't properly support a change attribute and are > subject to the same problems with timestamp granularity. Other > applications have similar issues with timestamps (e.g backup > applications). > > If we were to always use fine-grained timestamps, that would improve the > situation, but that becomes rather expensive, as the underlying > filesystem would have to log a lot more metadata updates. > > What we need is a way to only use fine-grained timestamps when they are > being actively queried. Use the (unused) top bit in inode->i_ctime_nsec > as a flag that indicates whether the current timestamps have been > queried via stat() or the like. When it's set, we allow the kernel to > use a fine-grained timestamp iff it's necessary to make the ctime show > a different value. > > This solves the problem of being able to distinguish the timestamp > between updates, but introduces a new problem: it's now possible for a > file being changed to get a fine-grained timestamp. A file that is > altered just a bit later can then get a coarse-grained one that appears > older than the earlier fine-grained time. This violates timestamp > ordering guarantees. > > To remedy this, keep a global monotonic atomic64_t value that acts as a > timestamp floor. When we go to stamp a file, we first get the latter of > the current floor value and the current coarse-grained time. If the > inode ctime hasn't been queried then we just attempt to stamp it with > that value. > > If it has been queried, then first see whether the current coarse time > is later than the existing ctime. If it is, then we accept that value. > If it isn't, then we get a fine-grained time and try to swap that into > the global floor. Whether that succeeds or fails, we take the resulting > floor time, convert it to realtime and try to swap that into the ctime. > > We take the result of the ctime swap whether it succeeds or fails, since > either is just as valid. > > Filesystems can opt into this by setting the FS_MGTIME fstype flag. > Others should be unaffected (other than being subject to the same floor > value as multigrain filesystems). > > Reviewed-by: Darrick J. Wong <djwong@kernel.org> > Reviewed-by: Josef Bacik <josef@toxicpanda.com> > Signed-off-by: Jeff Layton <jlayton@kernel.org> Phew! Quite subtle in the end but it looks good to me. Feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > fs/inode.c | 176 +++++++++++++++++++++++++++++++++++++++++++++-------- > fs/stat.c | 36 ++++++++++- > include/linux/fs.h | 34 ++++++++--- > 3 files changed, 209 insertions(+), 37 deletions(-) > > diff --git a/fs/inode.c b/fs/inode.c > index f356fe2ec2b6..417acbeabef3 100644 > --- a/fs/inode.c > +++ b/fs/inode.c > @@ -60,6 +60,13 @@ static unsigned int i_hash_shift __ro_after_init; > static struct hlist_head *inode_hashtable __ro_after_init; > static __cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_hash_lock); > > +/* > + * This represents the latest fine-grained time that we have handed out as a > + * timestamp on the system. Tracked as a monotonic value, and converted to the > + * realtime clock on an as-needed basis. > + */ > +static __cacheline_aligned_in_smp atomic64_t ctime_floor; > + > /* > * Empty aops. Can be used for the cases where the user does not > * define any of the address_space operations. > @@ -2127,19 +2134,72 @@ int file_remove_privs(struct file *file) > } > EXPORT_SYMBOL(file_remove_privs); > > +/** > + * coarse_ctime - return the current coarse-grained time > + * @floor: current (monotonic) ctime_floor value > + * > + * Get the coarse-grained time, and then determine whether to > + * return it or the current floor value. Returns the later of the > + * floor and coarse grained timestamps, converted to realtime > + * clock value. > + */ > +static ktime_t coarse_ctime(ktime_t floor) > +{ > + ktime_t coarse = ktime_get_coarse(); > + > + /* If coarse time is already newer, return that */ > + if (!ktime_after(floor, coarse)) > + return ktime_get_coarse_real(); > + return ktime_mono_to_real(floor); > +} > + > +/** > + * current_time - Return FS time (possibly fine-grained) > + * @inode: inode. > + * > + * Return the current time truncated to the time granularity supported by > + * the fs, as suitable for a ctime/mtime change. If the ctime is flagged > + * as having been QUERIED, get a fine-grained timestamp. > + */ > +struct timespec64 current_time(struct inode *inode) > +{ > + ktime_t floor = atomic64_read(&ctime_floor); > + ktime_t now = coarse_ctime(floor); > + struct timespec64 now_ts = ktime_to_timespec64(now); > + u32 cns; > + > + if (!is_mgtime(inode)) > + goto out; > + > + /* If nothing has queried it, then coarse time is fine */ > + cns = smp_load_acquire(&inode->i_ctime_nsec); > + if (cns & I_CTIME_QUERIED) { > + /* > + * If there is no apparent change, then > + * get a fine-grained timestamp. > + */ > + if (now_ts.tv_nsec == (cns & ~I_CTIME_QUERIED)) > + ktime_get_real_ts64(&now_ts); > + } > +out: > + return timestamp_truncate(now_ts, inode); > +} > +EXPORT_SYMBOL(current_time); > + > static int inode_needs_update_time(struct inode *inode) > { > + struct timespec64 now, ts; > int sync_it = 0; > - struct timespec64 now = current_time(inode); > - struct timespec64 ts; > > /* First try to exhaust all avenues to not sync */ > if (IS_NOCMTIME(inode)) > return 0; > > + now = current_time(inode); > + > ts = inode_get_mtime(inode); > if (!timespec64_equal(&ts, &now)) > - sync_it = S_MTIME; > + sync_it |= S_MTIME; > > ts = inode_get_ctime(inode); > if (!timespec64_equal(&ts, &now)) > @@ -2507,6 +2567,15 @@ void inode_nohighmem(struct inode *inode) > } > EXPORT_SYMBOL(inode_nohighmem); > > +struct timespec64 inode_set_ctime_to_ts(struct inode *inode, struct timespec64 ts) > +{ > + set_normalized_timespec64(&ts, ts.tv_sec, ts.tv_nsec); > + inode->i_ctime_sec = ts.tv_sec; > + inode->i_ctime_nsec = ts.tv_nsec; > + return ts; > +} > +EXPORT_SYMBOL(inode_set_ctime_to_ts); > + > /** > * timestamp_truncate - Truncate timespec to a granularity > * @t: Timespec > @@ -2538,38 +2607,91 @@ struct timespec64 timestamp_truncate(struct timespec64 t, struct inode *inode) > } > EXPORT_SYMBOL(timestamp_truncate); > > -/** > - * current_time - Return FS time > - * @inode: inode. > - * > - * Return the current time truncated to the time granularity supported by > - * the fs. > - * > - * Note that inode and inode->sb cannot be NULL. > - * Otherwise, the function warns and returns time without truncation. > - */ > -struct timespec64 current_time(struct inode *inode) > -{ > - struct timespec64 now; > - > - ktime_get_coarse_real_ts64(&now); > - return timestamp_truncate(now, inode); > -} > -EXPORT_SYMBOL(current_time); > - > /** > * inode_set_ctime_current - set the ctime to current_time > * @inode: inode > * > - * Set the inode->i_ctime to the current value for the inode. Returns > - * the current value that was assigned to i_ctime. > + * Set the inode's ctime to the current value for the inode. Returns the > + * current value that was assigned. If this is not a multigrain inode, then we > + * just set it to whatever the coarse_ctime is. > + * > + * If it is multigrain, then we first see if the coarse-grained timestamp is > + * distinct from what we have. If so, then we'll just use that. If we have to > + * get a fine-grained timestamp, then do so, and try to swap it into the floor. > + * We accept the new floor value regardless of the outcome of the cmpxchg. > + * After that, we try to swap the new value into i_ctime_nsec. Again, we take > + * the resulting ctime, regardless of the outcome of the swap. > */ > struct timespec64 inode_set_ctime_current(struct inode *inode) > { > - struct timespec64 now = current_time(inode); > + ktime_t now, floor = atomic64_read(&ctime_floor); > + struct timespec64 now_ts; > + u32 cns, cur; > + > + now = coarse_ctime(floor); > + > + /* Just return that if this is not a multigrain fs */ > + if (!is_mgtime(inode)) { > + now_ts = timestamp_truncate(ktime_to_timespec64(now), inode); > + inode_set_ctime_to_ts(inode, now_ts); > + goto out; > + } > + > + /* > + * We only need a fine-grained time if someone has queried it, > + * and the current coarse grained time isn't later than what's > + * already there. > + */ > + cns = smp_load_acquire(&inode->i_ctime_nsec); > + if (cns & I_CTIME_QUERIED) { > + ktime_t ctime = ktime_set(inode->i_ctime_sec, cns & ~I_CTIME_QUERIED); > + > + if (!ktime_after(now, ctime)) { > + ktime_t old, fine; > + > + /* Get a fine-grained time */ > + fine = ktime_get(); > > - inode_set_ctime_to_ts(inode, now); > - return now; > + /* > + * If the cmpxchg works, we take the new floor value. If > + * not, then that means that someone else changed it after we > + * fetched it but before we got here. That value is just > + * as good, so keep it. > + */ > + old = floor; > + if (!atomic64_try_cmpxchg(&ctime_floor, &old, fine)) > + fine = old; > + now = ktime_mono_to_real(fine); > + } > + } > + now_ts = timestamp_truncate(ktime_to_timespec64(now), inode); > + cur = cns; > + > + /* No need to cmpxchg if it's exactly the same */ > + if (cns == now_ts.tv_nsec && inode->i_ctime_sec == now_ts.tv_sec) > + goto out; > +retry: > + /* Try to swap the nsec value into place. */ > + if (try_cmpxchg(&inode->i_ctime_nsec, &cur, now_ts.tv_nsec)) { > + /* If swap occurred, then we're (mostly) done */ > + inode->i_ctime_sec = now_ts.tv_sec; > + } else { > + /* > + * 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 (!(cns & I_CTIME_QUERIED) && (cns | I_CTIME_QUERIED) == cur) { > + cns = cur; > + goto retry; > + } > + /* Otherwise, keep the existing ctime */ > + now_ts.tv_sec = inode->i_ctime_sec; > + now_ts.tv_nsec = cur & ~I_CTIME_QUERIED; > + } > +out: > + return now_ts; > } > EXPORT_SYMBOL(inode_set_ctime_current); > > diff --git a/fs/stat.c b/fs/stat.c > index 6f65b3456cad..df7fdd3afed9 100644 > --- a/fs/stat.c > +++ b/fs/stat.c > @@ -26,6 +26,32 @@ > #include "internal.h" > #include "mount.h" > > +/** > + * fill_mg_cmtime - Fill in the mtime and ctime and flag ctime as QUERIED > + * @stat: where to store the resulting values > + * @request_mask: STATX_* values requested > + * @inode: inode from which to grab the c/mtime > + * > + * Given @inode, grab the ctime and mtime out if it and store the result > + * in @stat. When fetching the value, flag it as queried so the next write > + * will ensure a distinct timestamp. > + */ > +void fill_mg_cmtime(struct kstat *stat, u32 request_mask, struct inode *inode) > +{ > + atomic_t *pcn = (atomic_t *)&inode->i_ctime_nsec; > + > + /* If neither time was requested, then don't report them */ > + if (!(request_mask & (STATX_CTIME|STATX_MTIME))) { > + stat->result_mask &= ~(STATX_CTIME|STATX_MTIME); > + return; > + } > + > + stat->mtime = inode_get_mtime(inode); > + stat->ctime.tv_sec = inode->i_ctime_sec; > + stat->ctime.tv_nsec = ((u32)atomic_fetch_or(I_CTIME_QUERIED, pcn)) & ~I_CTIME_QUERIED; > +} > +EXPORT_SYMBOL(fill_mg_cmtime); > + > /** > * generic_fillattr - Fill in the basic attributes from the inode struct > * @idmap: idmap of the mount the inode was found from > @@ -58,8 +84,14 @@ void generic_fillattr(struct mnt_idmap *idmap, u32 request_mask, > stat->rdev = inode->i_rdev; > stat->size = i_size_read(inode); > stat->atime = inode_get_atime(inode); > - stat->mtime = inode_get_mtime(inode); > - stat->ctime = inode_get_ctime(inode); > + > + if (is_mgtime(inode)) { > + fill_mg_cmtime(stat, request_mask, inode); > + } else { > + stat->ctime = inode_get_ctime(inode); > + stat->mtime = inode_get_mtime(inode); > + } > + > stat->blksize = i_blocksize(inode); > stat->blocks = inode->i_blocks; > > diff --git a/include/linux/fs.h b/include/linux/fs.h > index dc9f9c4b2572..f873f6c58669 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -1608,6 +1608,17 @@ static inline struct timespec64 inode_set_mtime(struct inode *inode, > return inode_set_mtime_to_ts(inode, ts); > } > > +/* > + * Multigrain timestamps > + * > + * Conditionally use fine-grained ctime and mtime timestamps when there > + * are users actively observing them via getattr. The primary use-case > + * for this is NFS clients that use the ctime to distinguish between > + * different states of the file, and that are often fooled by multiple > + * operations that occur in the same coarse-grained timer tick. > + */ > +#define I_CTIME_QUERIED ((u32)BIT(31)) > + > static inline time64_t inode_get_ctime_sec(const struct inode *inode) > { > return inode->i_ctime_sec; > @@ -1615,7 +1626,7 @@ static inline time64_t inode_get_ctime_sec(const struct inode *inode) > > static inline long inode_get_ctime_nsec(const struct inode *inode) > { > - return inode->i_ctime_nsec; > + return inode->i_ctime_nsec & ~I_CTIME_QUERIED; > } > > static inline struct timespec64 inode_get_ctime(const struct inode *inode) > @@ -1626,13 +1637,7 @@ static inline struct timespec64 inode_get_ctime(const struct inode *inode) > return ts; > } > > -static inline struct timespec64 inode_set_ctime_to_ts(struct inode *inode, > - struct timespec64 ts) > -{ > - inode->i_ctime_sec = ts.tv_sec; > - inode->i_ctime_nsec = ts.tv_nsec; > - return ts; > -} > +struct timespec64 inode_set_ctime_to_ts(struct inode *inode, struct timespec64 ts); > > /** > * inode_set_ctime - set the ctime in the inode > @@ -2490,6 +2495,7 @@ struct file_system_type { > #define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */ > #define FS_DISALLOW_NOTIFY_PERM 16 /* Disable fanotify permission events */ > #define FS_ALLOW_IDMAP 32 /* FS has been updated to handle vfs idmappings. */ > +#define FS_MGTIME 64 /* FS uses multigrain timestamps */ > #define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */ > int (*init_fs_context)(struct fs_context *); > const struct fs_parameter_spec *parameters; > @@ -2513,6 +2519,17 @@ struct file_system_type { > > #define MODULE_ALIAS_FS(NAME) MODULE_ALIAS("fs-" NAME) > > +/** > + * is_mgtime: is this inode using multigrain timestamps > + * @inode: inode to test for multigrain timestamps > + * > + * Return true if the inode uses multigrain timestamps, false otherwise. > + */ > +static inline bool is_mgtime(const struct inode *inode) > +{ > + return inode->i_sb->s_type->fs_flags & FS_MGTIME; > +} > + > extern struct dentry *mount_bdev(struct file_system_type *fs_type, > int flags, const char *dev_name, void *data, > int (*fill_super)(struct super_block *, void *, int)); > @@ -3252,6 +3269,7 @@ extern void page_put_link(void *); > extern int page_symlink(struct inode *inode, const char *symname, int len); > extern const struct inode_operations page_symlink_inode_operations; > extern void kfree_link(void *); > +void fill_mg_cmtime(struct kstat *stat, u32 request_mask, struct inode *inode); > void generic_fillattr(struct mnt_idmap *, u32, struct inode *, struct kstat *); > void generic_fill_statx_attr(struct inode *inode, struct kstat *stat); > extern int vfs_getattr_nosec(const struct path *, struct kstat *, u32, unsigned int); > > -- > 2.45.2 >
diff --git a/fs/inode.c b/fs/inode.c index f356fe2ec2b6..417acbeabef3 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -60,6 +60,13 @@ static unsigned int i_hash_shift __ro_after_init; static struct hlist_head *inode_hashtable __ro_after_init; static __cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_hash_lock); +/* + * This represents the latest fine-grained time that we have handed out as a + * timestamp on the system. Tracked as a monotonic value, and converted to the + * realtime clock on an as-needed basis. + */ +static __cacheline_aligned_in_smp atomic64_t ctime_floor; + /* * Empty aops. Can be used for the cases where the user does not * define any of the address_space operations. @@ -2127,19 +2134,72 @@ int file_remove_privs(struct file *file) } EXPORT_SYMBOL(file_remove_privs); +/** + * coarse_ctime - return the current coarse-grained time + * @floor: current (monotonic) ctime_floor value + * + * Get the coarse-grained time, and then determine whether to + * return it or the current floor value. Returns the later of the + * floor and coarse grained timestamps, converted to realtime + * clock value. + */ +static ktime_t coarse_ctime(ktime_t floor) +{ + ktime_t coarse = ktime_get_coarse(); + + /* If coarse time is already newer, return that */ + if (!ktime_after(floor, coarse)) + return ktime_get_coarse_real(); + return ktime_mono_to_real(floor); +} + +/** + * current_time - Return FS time (possibly fine-grained) + * @inode: inode. + * + * Return the current time truncated to the time granularity supported by + * the fs, as suitable for a ctime/mtime change. If the ctime is flagged + * as having been QUERIED, get a fine-grained timestamp. + */ +struct timespec64 current_time(struct inode *inode) +{ + ktime_t floor = atomic64_read(&ctime_floor); + ktime_t now = coarse_ctime(floor); + struct timespec64 now_ts = ktime_to_timespec64(now); + u32 cns; + + if (!is_mgtime(inode)) + goto out; + + /* If nothing has queried it, then coarse time is fine */ + cns = smp_load_acquire(&inode->i_ctime_nsec); + if (cns & I_CTIME_QUERIED) { + /* + * If there is no apparent change, then + * get a fine-grained timestamp. + */ + if (now_ts.tv_nsec == (cns & ~I_CTIME_QUERIED)) + ktime_get_real_ts64(&now_ts); + } +out: + return timestamp_truncate(now_ts, inode); +} +EXPORT_SYMBOL(current_time); + static int inode_needs_update_time(struct inode *inode) { + struct timespec64 now, ts; int sync_it = 0; - struct timespec64 now = current_time(inode); - struct timespec64 ts; /* First try to exhaust all avenues to not sync */ if (IS_NOCMTIME(inode)) return 0; + now = current_time(inode); + ts = inode_get_mtime(inode); if (!timespec64_equal(&ts, &now)) - sync_it = S_MTIME; + sync_it |= S_MTIME; ts = inode_get_ctime(inode); if (!timespec64_equal(&ts, &now)) @@ -2507,6 +2567,15 @@ void inode_nohighmem(struct inode *inode) } EXPORT_SYMBOL(inode_nohighmem); +struct timespec64 inode_set_ctime_to_ts(struct inode *inode, struct timespec64 ts) +{ + set_normalized_timespec64(&ts, ts.tv_sec, ts.tv_nsec); + inode->i_ctime_sec = ts.tv_sec; + inode->i_ctime_nsec = ts.tv_nsec; + return ts; +} +EXPORT_SYMBOL(inode_set_ctime_to_ts); + /** * timestamp_truncate - Truncate timespec to a granularity * @t: Timespec @@ -2538,38 +2607,91 @@ struct timespec64 timestamp_truncate(struct timespec64 t, struct inode *inode) } EXPORT_SYMBOL(timestamp_truncate); -/** - * current_time - Return FS time - * @inode: inode. - * - * Return the current time truncated to the time granularity supported by - * the fs. - * - * Note that inode and inode->sb cannot be NULL. - * Otherwise, the function warns and returns time without truncation. - */ -struct timespec64 current_time(struct inode *inode) -{ - struct timespec64 now; - - ktime_get_coarse_real_ts64(&now); - return timestamp_truncate(now, inode); -} -EXPORT_SYMBOL(current_time); - /** * inode_set_ctime_current - set the ctime to current_time * @inode: inode * - * Set the inode->i_ctime to the current value for the inode. Returns - * the current value that was assigned to i_ctime. + * Set the inode's ctime to the current value for the inode. Returns the + * current value that was assigned. If this is not a multigrain inode, then we + * just set it to whatever the coarse_ctime is. + * + * If it is multigrain, then we first see if the coarse-grained timestamp is + * distinct from what we have. If so, then we'll just use that. If we have to + * get a fine-grained timestamp, then do so, and try to swap it into the floor. + * We accept the new floor value regardless of the outcome of the cmpxchg. + * After that, we try to swap the new value into i_ctime_nsec. Again, we take + * the resulting ctime, regardless of the outcome of the swap. */ struct timespec64 inode_set_ctime_current(struct inode *inode) { - struct timespec64 now = current_time(inode); + ktime_t now, floor = atomic64_read(&ctime_floor); + struct timespec64 now_ts; + u32 cns, cur; + + now = coarse_ctime(floor); + + /* Just return that if this is not a multigrain fs */ + if (!is_mgtime(inode)) { + now_ts = timestamp_truncate(ktime_to_timespec64(now), inode); + inode_set_ctime_to_ts(inode, now_ts); + goto out; + } + + /* + * We only need a fine-grained time if someone has queried it, + * and the current coarse grained time isn't later than what's + * already there. + */ + cns = smp_load_acquire(&inode->i_ctime_nsec); + if (cns & I_CTIME_QUERIED) { + ktime_t ctime = ktime_set(inode->i_ctime_sec, cns & ~I_CTIME_QUERIED); + + if (!ktime_after(now, ctime)) { + ktime_t old, fine; + + /* Get a fine-grained time */ + fine = ktime_get(); - inode_set_ctime_to_ts(inode, now); - return now; + /* + * If the cmpxchg works, we take the new floor value. If + * not, then that means that someone else changed it after we + * fetched it but before we got here. That value is just + * as good, so keep it. + */ + old = floor; + if (!atomic64_try_cmpxchg(&ctime_floor, &old, fine)) + fine = old; + now = ktime_mono_to_real(fine); + } + } + now_ts = timestamp_truncate(ktime_to_timespec64(now), inode); + cur = cns; + + /* No need to cmpxchg if it's exactly the same */ + if (cns == now_ts.tv_nsec && inode->i_ctime_sec == now_ts.tv_sec) + goto out; +retry: + /* Try to swap the nsec value into place. */ + if (try_cmpxchg(&inode->i_ctime_nsec, &cur, now_ts.tv_nsec)) { + /* If swap occurred, then we're (mostly) done */ + inode->i_ctime_sec = now_ts.tv_sec; + } else { + /* + * 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 (!(cns & I_CTIME_QUERIED) && (cns | I_CTIME_QUERIED) == cur) { + cns = cur; + goto retry; + } + /* Otherwise, keep the existing ctime */ + now_ts.tv_sec = inode->i_ctime_sec; + now_ts.tv_nsec = cur & ~I_CTIME_QUERIED; + } +out: + return now_ts; } EXPORT_SYMBOL(inode_set_ctime_current); diff --git a/fs/stat.c b/fs/stat.c index 6f65b3456cad..df7fdd3afed9 100644 --- a/fs/stat.c +++ b/fs/stat.c @@ -26,6 +26,32 @@ #include "internal.h" #include "mount.h" +/** + * fill_mg_cmtime - Fill in the mtime and ctime and flag ctime as QUERIED + * @stat: where to store the resulting values + * @request_mask: STATX_* values requested + * @inode: inode from which to grab the c/mtime + * + * Given @inode, grab the ctime and mtime out if it and store the result + * in @stat. When fetching the value, flag it as queried so the next write + * will ensure a distinct timestamp. + */ +void fill_mg_cmtime(struct kstat *stat, u32 request_mask, struct inode *inode) +{ + atomic_t *pcn = (atomic_t *)&inode->i_ctime_nsec; + + /* If neither time was requested, then don't report them */ + if (!(request_mask & (STATX_CTIME|STATX_MTIME))) { + stat->result_mask &= ~(STATX_CTIME|STATX_MTIME); + return; + } + + stat->mtime = inode_get_mtime(inode); + stat->ctime.tv_sec = inode->i_ctime_sec; + stat->ctime.tv_nsec = ((u32)atomic_fetch_or(I_CTIME_QUERIED, pcn)) & ~I_CTIME_QUERIED; +} +EXPORT_SYMBOL(fill_mg_cmtime); + /** * generic_fillattr - Fill in the basic attributes from the inode struct * @idmap: idmap of the mount the inode was found from @@ -58,8 +84,14 @@ void generic_fillattr(struct mnt_idmap *idmap, u32 request_mask, stat->rdev = inode->i_rdev; stat->size = i_size_read(inode); stat->atime = inode_get_atime(inode); - stat->mtime = inode_get_mtime(inode); - stat->ctime = inode_get_ctime(inode); + + if (is_mgtime(inode)) { + fill_mg_cmtime(stat, request_mask, inode); + } else { + stat->ctime = inode_get_ctime(inode); + stat->mtime = inode_get_mtime(inode); + } + stat->blksize = i_blocksize(inode); stat->blocks = inode->i_blocks; diff --git a/include/linux/fs.h b/include/linux/fs.h index dc9f9c4b2572..f873f6c58669 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1608,6 +1608,17 @@ static inline struct timespec64 inode_set_mtime(struct inode *inode, return inode_set_mtime_to_ts(inode, ts); } +/* + * Multigrain timestamps + * + * Conditionally use fine-grained ctime and mtime timestamps when there + * are users actively observing them via getattr. The primary use-case + * for this is NFS clients that use the ctime to distinguish between + * different states of the file, and that are often fooled by multiple + * operations that occur in the same coarse-grained timer tick. + */ +#define I_CTIME_QUERIED ((u32)BIT(31)) + static inline time64_t inode_get_ctime_sec(const struct inode *inode) { return inode->i_ctime_sec; @@ -1615,7 +1626,7 @@ static inline time64_t inode_get_ctime_sec(const struct inode *inode) static inline long inode_get_ctime_nsec(const struct inode *inode) { - return inode->i_ctime_nsec; + return inode->i_ctime_nsec & ~I_CTIME_QUERIED; } static inline struct timespec64 inode_get_ctime(const struct inode *inode) @@ -1626,13 +1637,7 @@ static inline struct timespec64 inode_get_ctime(const struct inode *inode) return ts; } -static inline struct timespec64 inode_set_ctime_to_ts(struct inode *inode, - struct timespec64 ts) -{ - inode->i_ctime_sec = ts.tv_sec; - inode->i_ctime_nsec = ts.tv_nsec; - return ts; -} +struct timespec64 inode_set_ctime_to_ts(struct inode *inode, struct timespec64 ts); /** * inode_set_ctime - set the ctime in the inode @@ -2490,6 +2495,7 @@ struct file_system_type { #define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */ #define FS_DISALLOW_NOTIFY_PERM 16 /* Disable fanotify permission events */ #define FS_ALLOW_IDMAP 32 /* FS has been updated to handle vfs idmappings. */ +#define FS_MGTIME 64 /* FS uses multigrain timestamps */ #define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */ int (*init_fs_context)(struct fs_context *); const struct fs_parameter_spec *parameters; @@ -2513,6 +2519,17 @@ struct file_system_type { #define MODULE_ALIAS_FS(NAME) MODULE_ALIAS("fs-" NAME) +/** + * is_mgtime: is this inode using multigrain timestamps + * @inode: inode to test for multigrain timestamps + * + * Return true if the inode uses multigrain timestamps, false otherwise. + */ +static inline bool is_mgtime(const struct inode *inode) +{ + return inode->i_sb->s_type->fs_flags & FS_MGTIME; +} + extern struct dentry *mount_bdev(struct file_system_type *fs_type, int flags, const char *dev_name, void *data, int (*fill_super)(struct super_block *, void *, int)); @@ -3252,6 +3269,7 @@ extern void page_put_link(void *); extern int page_symlink(struct inode *inode, const char *symname, int len); extern const struct inode_operations page_symlink_inode_operations; extern void kfree_link(void *); +void fill_mg_cmtime(struct kstat *stat, u32 request_mask, struct inode *inode); void generic_fillattr(struct mnt_idmap *, u32, struct inode *, struct kstat *); void generic_fill_statx_attr(struct inode *inode, struct kstat *stat); extern int vfs_getattr_nosec(const struct path *, struct kstat *, u32, unsigned int);