signal: Use PIDTYPE_TGID to clearly store where file signals will be sent

When f_setown is called a pid and a pid type are stored.  Replace the use
of PIDTYPE_PID with PIDTYPE_TGID as PIDTYPE_TGID goes to the entire thread
group.  Replace the use of PIDTYPE_MAX with PIDTYPE_PID as PIDTYPE_PID now
is only for a thread.

Update the users of __f_setown to use PIDTYPE_TGID instead of
PIDTYPE_PID.

For now the code continues to capture task_pid (when task_tgid would
really be appropriate), and iterate on PIDTYPE_PID (even when type ==
PIDTYPE_TGID) out of an abundance of caution to preserve existing
behavior.

Oleg Nesterov suggested using the test to ensure we use PIDTYPE_PID
for tgid lookup also be used to avoid taking the tasklist lock.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 32 insertions, 22 deletions

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 12273b6ea56d..1523588fd759 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -116,7 +116,7 @@ int f_setown(struct file *filp, unsigned long arg, int force)
         struct pid *pid = NULL;
         int who = arg, ret = 0;
 
-        type = PIDTYPE_PID;
+        type = PIDTYPE_TGID;
         if (who < 0) {
                 /* avoid overflow below */
                 if (who == INT_MIN)
@@ -143,7 +143,7 @@ EXPORT_SYMBOL(f_setown);
 
 void f_delown(struct file *filp)
 {
-        f_modown(filp, NULL, PIDTYPE_PID, 1);
+        f_modown(filp, NULL, PIDTYPE_TGID, 1);
 }
 
 pid_t f_getown(struct file *filp)
@@ -171,11 +171,11 @@ static int f_setown_ex(struct file *filp, unsigned long arg)
 
         switch (owner.type) {
         case F_OWNER_TID:
-                type = PIDTYPE_MAX;
+                type = PIDTYPE_PID;
                 break;
 
         case F_OWNER_PID:
-                type = PIDTYPE_PID;
+                type = PIDTYPE_TGID;
                 break;
 
         case F_OWNER_PGRP:
@@ -206,11 +206,11 @@ static int f_getown_ex(struct file *filp, unsigned long arg)
         read_lock(&filp->f_owner.lock);
         owner.pid = pid_vnr(filp->f_owner.pid);
         switch (filp->f_owner.pid_type) {
-        case PIDTYPE_MAX:
+        case PIDTYPE_PID:
                 owner.type = F_OWNER_TID;
                 break;
 
-        case PIDTYPE_PID:
+        case PIDTYPE_TGID:
                 owner.type = F_OWNER_PID;
                 break;
 
@@ -785,20 +785,25 @@ void send_sigio(struct fown_struct *fown, int fd, int band)
         read_lock(&fown->lock);
 
         type = fown->pid_type;
-        if (type == PIDTYPE_MAX) {
+        if (type == PIDTYPE_PID)
                 group = 0;
-                type = PIDTYPE_PID;
-        }
 
         pid = fown->pid;
         if (!pid)
                 goto out_unlock_fown;
-        
-        read_lock(&tasklist_lock);
-        do_each_pid_task(pid, type, p) {
+
+        if (type <= PIDTYPE_TGID) {
+                rcu_read_lock();
+                p = pid_task(pid, PIDTYPE_PID);
                 send_sigio_to_task(p, fown, fd, band, group);
-        } while_each_pid_task(pid, type, p);
-        read_unlock(&tasklist_lock);
+                rcu_read_unlock();
+        } else {
+                read_lock(&tasklist_lock);
+                do_each_pid_task(pid, type, p) {
+                        send_sigio_to_task(p, fown, fd, band, group);
+                } while_each_pid_task(pid, type, p);
+                read_unlock(&tasklist_lock);
+        }
  out_unlock_fown:
         read_unlock(&fown->lock);
 }
@@ -821,22 +826,27 @@ int send_sigurg(struct fown_struct *fown)
         read_lock(&fown->lock);
 
         type = fown->pid_type;
-        if (type == PIDTYPE_MAX) {
+        if (type == PIDTYPE_PID)
                 group = 0;
-                type = PIDTYPE_PID;
-        }
 
         pid = fown->pid;
         if (!pid)
                 goto out_unlock_fown;
 
         ret = 1;
-        
-        read_lock(&tasklist_lock);
-        do_each_pid_task(pid, type, p) {
+
+        if (type <= PIDTYPE_TGID) {
+                rcu_read_lock();
+                p = pid_task(pid, PIDTYPE_PID);
                 send_sigurg_to_task(p, fown, group);
-        } while_each_pid_task(pid, type, p);
-        read_unlock(&tasklist_lock);
+                rcu_read_unlock();
+        } else {
+                read_lock(&tasklist_lock);
+                do_each_pid_task(pid, type, p) {
+                        send_sigurg_to_task(p, fown, group);
+                } while_each_pid_task(pid, type, p);
+                read_unlock(&tasklist_lock);
+        }
  out_unlock_fown:
         read_unlock(&fown->lock);
         return ret;