On Mon, Feb 10, 2020 at 07:36:08PM -0600, Eric W. Biederman wrote: > Alexey Gladkov <gladkov.alexey@xxxxxxxxx> writes: > > > This allows to flush dcache entries of a task on multiple procfs mounts > > per pid namespace. > > > > The RCU lock is used because the number of reads at the task exit time > > is much larger than the number of procfs mounts. > > A couple of quick comments. > > > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > > Cc: Andy Lutomirski <luto@xxxxxxxxxx> > > Signed-off-by: Djalal Harouni <tixxdz@xxxxxxxxx> > > Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > > Signed-off-by: Alexey Gladkov <gladkov.alexey@xxxxxxxxx> > > --- > > fs/proc/base.c | 20 +++++++++++++++----- > > fs/proc/root.c | 27 ++++++++++++++++++++++++++- > > include/linux/pid_namespace.h | 2 ++ > > include/linux/proc_fs.h | 2 ++ > > 4 files changed, 45 insertions(+), 6 deletions(-) > > > > diff --git a/fs/proc/base.c b/fs/proc/base.c > > index 4ccb280a3e79..24b7c620ded3 100644 > > --- a/fs/proc/base.c > > +++ b/fs/proc/base.c > > @@ -3133,7 +3133,7 @@ static const struct inode_operations proc_tgid_base_inode_operations = { > > .permission = proc_pid_permission, > > }; > > > > -static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid) > > +static void proc_flush_task_mnt_root(struct dentry *mnt_root, pid_t pid, pid_t tgid) > Perhaps just rename things like: > > +static void proc_flush_task_root(struct dentry *root, pid_t pid, pid_t tgid) > > { > > I don't think the mnt_ prefix conveys any information, and it certainly > makes everything longer and more cumbersome. > > > struct dentry *dentry, *leader, *dir; > > char buf[10 + 1]; > > @@ -3142,7 +3142,7 @@ static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid) > > name.name = buf; > > name.len = snprintf(buf, sizeof(buf), "%u", pid); > > /* no ->d_hash() rejects on procfs */ > > - dentry = d_hash_and_lookup(mnt->mnt_root, &name); > > + dentry = d_hash_and_lookup(mnt_root, &name); > > if (dentry) { > > d_invalidate(dentry); > > dput(dentry); > > @@ -3153,7 +3153,7 @@ static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid) > > > > name.name = buf; > > name.len = snprintf(buf, sizeof(buf), "%u", tgid); > > - leader = d_hash_and_lookup(mnt->mnt_root, &name); > > + leader = d_hash_and_lookup(mnt_root, &name); > > if (!leader) > > goto out; > > > > @@ -3208,14 +3208,24 @@ void proc_flush_task(struct task_struct *task) > > int i; > > struct pid *pid, *tgid; > > struct upid *upid; > > + struct dentry *mnt_root; > > + struct proc_fs_info *fs_info; > > > > pid = task_pid(task); > > tgid = task_tgid(task); > > > > for (i = 0; i <= pid->level; i++) { > > upid = &pid->numbers[i]; > > - proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr, > > - tgid->numbers[i].nr); > > + > > + rcu_read_lock(); > > + list_for_each_entry_rcu(fs_info, &upid->ns->proc_mounts, pidns_entry) { > > + mnt_root = fs_info->m_super->s_root; > > + proc_flush_task_mnt_root(mnt_root, upid->nr, tgid->numbers[i].nr); > > + } > > + rcu_read_unlock(); > > + > > + mnt_root = upid->ns->proc_mnt->mnt_root; > > + proc_flush_task_mnt_root(mnt_root, upid->nr, tgid->numbers[i].nr); > > I don't think this following of proc_mnt is needed. It certainly > shouldn't be. The loop through all of the super blocks should be > enough. Yes, thanks! > Once this change goes through. UML can be given it's own dedicated > proc_mnt for the initial pid namespace, and proc_mnt can be removed > entirely. After you deleted the old sysctl syscall we could probably do it. > Unless something has changed recently UML is the only other user of > pid_ns->proc_mnt. That proc_mnt really only exists to make the loop in > proc_flush_task easy to write. Now I think, is there any way to get rid of proc_mounts or even proc_flush_task somehow. > It also probably makes sense to take the rcu_read_lock() over > that entire for loop. Al Viro pointed out to me that I cannot use rcu locks here :( -- Rgrds, legion