| Message ID | 55B5A0B0.7060604@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, 27 Jul 2015 11:08:32 +0800 Kinglong Mee <kinglongmee@gmail.com> wrote: > New helper legitimize_mntget for getting a mnt without setting > MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED, otherwise return NULL. > > v8, same as v6 > > Signed-off-by: Kinglong Mee <kinglongmee@gmail.com> > --- > fs/namespace.c | 19 +++++++++++++++++++ > include/linux/mount.h | 1 + > 2 files changed, 20 insertions(+) > > diff --git a/fs/namespace.c b/fs/namespace.c > index 2b8aa15..842cf57 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -1153,6 +1153,25 @@ struct vfsmount *mntget(struct vfsmount *mnt) > } > EXPORT_SYMBOL(mntget); > > +struct vfsmount *legitimize_mntget(struct vfsmount *vfsmnt) > +{ > + struct mount *mnt; > + > + if (vfsmnt == NULL) > + return NULL; > + > + read_seqlock_excl(&mount_lock); > + mnt = real_mount(vfsmnt); > + if (vfsmnt->mnt_flags & (MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED)) > + vfsmnt = NULL; > + else > + mnt_add_count(mnt, 1); > + read_sequnlock_excl(&mount_lock); > + > + return vfsmnt; > +} > +EXPORT_SYMBOL(legitimize_mntget); > + > struct vfsmount *mnt_clone_internal(struct path *path) > { > struct mount *p; > diff --git a/include/linux/mount.h b/include/linux/mount.h > index f822c3c..8ae9dc0 100644 > --- a/include/linux/mount.h > +++ b/include/linux/mount.h > @@ -79,6 +79,7 @@ extern void mnt_drop_write(struct vfsmount *mnt); > extern void mnt_drop_write_file(struct file *file); > extern void mntput(struct vfsmount *mnt); > extern struct vfsmount *mntget(struct vfsmount *mnt); > +extern struct vfsmount *legitimize_mntget(struct vfsmount *vfsmnt); > extern struct vfsmount *mnt_clone_internal(struct path *path); > extern int __mnt_is_readonly(struct vfsmount *mnt); > It is unfortunate that we seem to have to take the mount_lock global lock on every nfs request. I wonder if we can avoid that.... What if we did: seq = 0; retry: read_seqbegin_or_lock(&mount_lock, &seq); if (vfsmnt->mnt_flags & (MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED)) vfsmnt = NULL; else if (need_seqretry(&mount_lock, seq); goto retry; else { mnt_add_count(&mnt, 1); if (need_seqretry(&mount_lock, seq) || vfsmnt->mnt_flags & (MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED)) { mnt_add_count(&mnt, -1); goto retry; } } done_seqretry(&mount_lock, seq); Is there any risk from having a temporarily elevated mnt_count there? I can't see one, but there is clearly some complexity in managing that count. Thanks, NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 7/29/2015 10:06, NeilBrown wrote: > On Mon, 27 Jul 2015 11:08:32 +0800 Kinglong Mee <kinglongmee@gmail.com> > wrote: > >> New helper legitimize_mntget for getting a mnt without setting >> MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED, otherwise return NULL. >> >> v8, same as v6 >> >> Signed-off-by: Kinglong Mee <kinglongmee@gmail.com> >> --- >> fs/namespace.c | 19 +++++++++++++++++++ >> include/linux/mount.h | 1 + >> 2 files changed, 20 insertions(+) >> >> diff --git a/fs/namespace.c b/fs/namespace.c >> index 2b8aa15..842cf57 100644 >> --- a/fs/namespace.c >> +++ b/fs/namespace.c >> @@ -1153,6 +1153,25 @@ struct vfsmount *mntget(struct vfsmount *mnt) >> } >> EXPORT_SYMBOL(mntget); >> >> +struct vfsmount *legitimize_mntget(struct vfsmount *vfsmnt) >> +{ >> + struct mount *mnt; >> + >> + if (vfsmnt == NULL) >> + return NULL; >> + >> + read_seqlock_excl(&mount_lock); >> + mnt = real_mount(vfsmnt); >> + if (vfsmnt->mnt_flags & (MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED)) >> + vfsmnt = NULL; >> + else >> + mnt_add_count(mnt, 1); >> + read_sequnlock_excl(&mount_lock); >> + >> + return vfsmnt; >> +} >> +EXPORT_SYMBOL(legitimize_mntget); >> + >> struct vfsmount *mnt_clone_internal(struct path *path) >> { >> struct mount *p; >> diff --git a/include/linux/mount.h b/include/linux/mount.h >> index f822c3c..8ae9dc0 100644 >> --- a/include/linux/mount.h >> +++ b/include/linux/mount.h >> @@ -79,6 +79,7 @@ extern void mnt_drop_write(struct vfsmount *mnt); >> extern void mnt_drop_write_file(struct file *file); >> extern void mntput(struct vfsmount *mnt); >> extern struct vfsmount *mntget(struct vfsmount *mnt); >> +extern struct vfsmount *legitimize_mntget(struct vfsmount *vfsmnt); >> extern struct vfsmount *mnt_clone_internal(struct path *path); >> extern int __mnt_is_readonly(struct vfsmount *mnt); >> > > It is unfortunate that we seem to have to take the mount_lock global > lock on every nfs request. I wonder if we can avoid that.... > > What if we did: > > seq = 0; > retry: > read_seqbegin_or_lock(&mount_lock, &seq); > if (vfsmnt->mnt_flags & (MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED)) > vfsmnt = NULL; > else if (need_seqretry(&mount_lock, seq); > goto retry; > else { > mnt_add_count(&mnt, 1); > if (need_seqretry(&mount_lock, seq) || > vfsmnt->mnt_flags & (MNT_SYNC_UMOUNT | MNT_UMOUNT | > MNT_DOOMED)) { > mnt_add_count(&mnt, -1); > goto retry; > } > } > done_seqretry(&mount_lock, seq); I don't really understand the seqlock, I will have a check about it. > > > Is there any risk from having a temporarily elevated mnt_count there? > I can't see one, but there is clearly some complexity in managing that > count. Yes, it's more complex than the above patch. But, if it can avoid taking the mount_lock every nfs request, I'd like it. I will test it later. thanks, Kinglong Mee -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/namespace.c b/fs/namespace.c index 2b8aa15..842cf57 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1153,6 +1153,25 @@ struct vfsmount *mntget(struct vfsmount *mnt) } EXPORT_SYMBOL(mntget); +struct vfsmount *legitimize_mntget(struct vfsmount *vfsmnt) +{ + struct mount *mnt; + + if (vfsmnt == NULL) + return NULL; + + read_seqlock_excl(&mount_lock); + mnt = real_mount(vfsmnt); + if (vfsmnt->mnt_flags & (MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED)) + vfsmnt = NULL; + else + mnt_add_count(mnt, 1); + read_sequnlock_excl(&mount_lock); + + return vfsmnt; +} +EXPORT_SYMBOL(legitimize_mntget); + struct vfsmount *mnt_clone_internal(struct path *path) { struct mount *p; diff --git a/include/linux/mount.h b/include/linux/mount.h index f822c3c..8ae9dc0 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -79,6 +79,7 @@ extern void mnt_drop_write(struct vfsmount *mnt); extern void mnt_drop_write_file(struct file *file); extern void mntput(struct vfsmount *mnt); extern struct vfsmount *mntget(struct vfsmount *mnt); +extern struct vfsmount *legitimize_mntget(struct vfsmount *vfsmnt); extern struct vfsmount *mnt_clone_internal(struct path *path); extern int __mnt_is_readonly(struct vfsmount *mnt);
New helper legitimize_mntget for getting a mnt without setting MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED, otherwise return NULL. v8, same as v6 Signed-off-by: Kinglong Mee <kinglongmee@gmail.com> --- fs/namespace.c | 19 +++++++++++++++++++ include/linux/mount.h | 1 + 2 files changed, 20 insertions(+)