From a872ff0cb2218dc9688b990c5ccda064dc40946b Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 26 Jun 2006 00:26:01 -0700 Subject: [PATCH] [PATCH] simplify/fix first_tid() first_tid: /* If nr exceeds the number of threads there is nothing todo */ if (nr) { if (nr >= get_nr_threads(leader)) goto done; } This is not reliable: sub-threads can exit after this check, so the 'for' loop below can overlap and proc_task_readdir() can return an already filldir'ed dirents. for (; pos && pid_alive(pos); pos = next_thread(pos)) { if (--nr > 0) continue; Off-by-one error, will return 'leader' when nr == 1. This patch tries to fix these problems and simplify the code. Signed-off-by: Oleg Nesterov Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/proc/base.c | 42 +++++++++++++++++++----------------------- 1 file changed, 19 insertions(+), 23 deletions(-) diff --git a/fs/proc/base.c b/fs/proc/base.c index 6092a6e2c5a9..5ee46d3a5cac 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2227,38 +2227,34 @@ int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir) static struct task_struct *first_tid(struct task_struct *leader, int tid, int nr) { - struct task_struct *pos = NULL; + struct task_struct *pos; rcu_read_lock(); /* Attempt to start with the pid of a thread */ if (tid && (nr > 0)) { pos = find_task_by_pid(tid); - if (pos && (pos->group_leader != leader)) - pos = NULL; - if (pos) - nr = 0; + if (pos && (pos->group_leader == leader)) + goto found; } /* If nr exceeds the number of threads there is nothing todo */ - if (nr) { - if (nr >= get_nr_threads(leader)) - goto done; - } - - /* If we haven't found our starting place yet start with the - * leader and walk nr threads forward. - */ - if (!pos && (nr >= 0)) - pos = leader; - - for (; pos && pid_alive(pos); pos = next_thread(pos)) { - if (--nr > 0) - continue; - get_task_struct(pos); - goto done; - } pos = NULL; -done: + if (nr && nr >= get_nr_threads(leader)) + goto out; + + /* If we haven't found our starting place yet start + * with the leader and walk nr threads forward. + */ + for (pos = leader; nr > 0; --nr) { + pos = next_thread(pos); + if (pos == leader) { + pos = NULL; + goto out; + } + } +found: + get_task_struct(pos); +out: rcu_read_unlock(); return pos; }