[PATCH v2 3/4] proc: simplify proc_task_readdir/first_tid paths

Oleg Nesterov
2013-06-03T19:10:58Z

proc_task_readdir() does not really need "leader", first_tid()
has to revalidate it anyway. Just pass proc_pid(inode) to
first_tid() instead, it can do pid_task(PIDTYPE_PID) itself
and read ->group_leader only if necessary.

The patch also extracts the "inode is dead" code
from pid_delete_dentry(dentry) into the new trivial helper,
proc_inode_is_dead(inode), proc_task_readdir() uses it to return
-ENOENT if this dir was removed. This is a bit racy, but the race
is very inlikely and the getdents() after openndir() can see the
empty "." + ".." dir only once.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
fs/proc/base.c | 53 ++++++++++++++++++++++-------------------------------
1 files changed, 22 insertions(+), 31 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index bed1096..5e0e02f 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1652,13 +1652,18 @@ int pid_revalidate(struct dentry *dentry, unsigned int flags)
return 0;
}

+static inline bool proc_inode_is_dead(struct inode *inode)
+{
+ return !proc_pid(inode)->tasks[PIDTYPE_PID].first;
+}
+
int pid_delete_dentry(const struct dentry *dentry)
{
/* Is the task we represent dead?
* If so, then don't put the dentry on the lru list,
* kill it immediately.
*/
- return !proc_pid(dentry->d_inode)->tasks[PIDTYPE_PID].first;
+ return proc_inode_is_dead(dentry->d_inode);
}

const struct dentry_operations pid_dentry_operations =
@@ -3173,34 +3178,35 @@ out_no_task:
* In the case of a seek we start with the leader and walk nr
* threads past it.
*/
-static struct task_struct *first_tid(struct task_struct *leader,
- int tid, int nr, struct pid_namespace *ns)
+static struct task_struct *first_tid(struct pid *pid, int tid,
+ int nr, struct pid_namespace *ns)
{
- struct task_struct *pos;
+ struct task_struct *pos, *task;

rcu_read_lock();
- /* Attempt to start with the pid of a thread */
+ task = pid_task(pid, PIDTYPE_PID);
+ if (!task)
+ goto fail;
+
+ /* Attempt to start with the tid of a thread */
if (tid && (nr > 0)) {
pos = find_task_by_pid_ns(tid, ns);
- if (pos && (pos->group_leader == leader))
+ if (pos && same_thread_group(pos, task))
goto found;
}

/* If nr exceeds the number of threads there is nothing todo */
- if (nr && nr >= get_nr_threads(leader))
- goto fail;
- /* It could be unhashed before we take rcu lock */
- if (!pid_alive(leader))
+ if (nr && nr >= get_nr_threads(task))
goto fail;

/* If we haven't found our starting place yet start
* with the leader and walk nr threads forward.
*/
- pos = leader;
+ pos = task = task->group_leader;
do {
if (nr-- <= 0)
goto found;
- } while_each_thread(leader, pos);
+ } while_each_thread(task, pos);
fail:
pos = NULL;
goto out;
@@ -3247,26 +3253,13 @@ static int proc_task_readdir(struct file * filp, void * dirent, filldir_t filldi
{
struct dentry *dentry = filp->f_path.dentry;
struct inode *inode = dentry->d_inode;
- struct task_struct *leader = NULL;
struct task_struct *task;
- int retval = -ENOENT;
ino_t ino;
int tid;
struct pid_namespace *ns;

- task = get_proc_task(inode);
- if (!task)
- goto out_no_task;
- rcu_read_lock();
- if (pid_alive(task)) {
- leader = task->group_leader;
- get_task_struct(leader);
- }
- rcu_read_unlock();
- put_task_struct(task);
- if (!leader)
- goto out_no_task;
- retval = 0;
+ if (proc_inode_is_dead(inode))
+ return -ENOENT;

switch ((unsigned long)filp->f_pos) {
case 0:
@@ -3289,7 +3282,7 @@ static int proc_task_readdir(struct file * filp, void * dirent, filldir_t filldi
ns = filp->f_dentry->d_sb->s_fs_info;
tid = (int)filp->f_version;
filp->f_version = 0;
- for (task = first_tid(leader, tid, filp->f_pos - 2, ns);
+ for (task = first_tid(proc_pid(inode), tid, filp->f_pos - 2, ns);
task;
task = next_tid(task), filp->f_pos++) {
tid = task_pid_nr_ns(task, ns);
@@ -3302,9 +3295,7 @@ static int proc_task_readdir(struct file * filp, void * dirent, filldir_t filldi
}
}
out:
- put_task_struct(leader);
-out_no_task:
- return retval;
+ return 0;
}

static int proc_task_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
--
1.5.5.1