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linux-sg2042
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[PATCH] signal, procfs: some lock_task_sighand() users do not need rcu_read_lock() 

lock_task_sighand() make sure task->sighand is being protected,
so we do not need rcu_read_lock().
[ exec() will get task->sighand->siglock before change task->sighand! ]

But code using rcu_read_lock() _just_ to protect lock_task_sighand()
only appear in procfs. (and some code in procfs use lock_task_sighand()
without such redundant protection.)

Other subsystem may put lock_task_sighand() into rcu_read_lock()
critical region, but these rcu_read_lock() are used for protecting
"for_each_process()", "find_task_by_vpid()" etc. , not for protecting
lock_task_sighand().

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
[ok from Oleg]
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
This commit is contained in:
Lai Jiangshan 2008-10-05 00:51:15 +04:00 committed by Alexey Dobriyan
parent 53167a3ef2
commit a6bebbc87a
3 changed files with 1 additions and 12 deletions
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2
fs/proc/array.c
View File

@ -261,7 +261,6 @@ static inline void task_sig(struct seq_file *m, struct task_struct *p)
sigemptyset(&ignored);
sigemptyset(&caught);
rcu_read_lock();
if (lock_task_sighand(p, &flags)) {
pending = p->pending.signal;
shpending = p->signal->shared_pending.signal;
@ -272,7 +271,6 @@ static inline void task_sig(struct seq_file *m, struct task_struct *p)
qlim = p->signal->rlim[RLIMIT_SIGPENDING].rlim_cur;
unlock_task_sighand(p, &flags);
}
rcu_read_unlock();
seq_printf(m, "Threads:\t%d\n", num_threads);
seq_printf(m, "SigQ:\t%lu/%lu\n", qsize, qlim);

9
fs/proc/base.c
View File

@ -164,7 +164,6 @@ static struct fs_struct *get_fs_struct(struct task_struct *task)
static int get_nr_threads(struct task_struct *tsk)
{
/* Must be called with the rcu_read_lock held */
unsigned long flags;
int count = 0;
@ -471,14 +470,10 @@ static int proc_pid_limits(struct task_struct *task, char *buffer)
struct rlimit rlim[RLIM_NLIMITS];
rcu_read_lock();
if (!lock_task_sighand(task,&flags)) {
rcu_read_unlock();
if (!lock_task_sighand(task, &flags))
return 0;
}
memcpy(rlim, task->signal->rlim, sizeof(struct rlimit) * RLIM_NLIMITS);
unlock_task_sighand(task, &flags);
rcu_read_unlock();
/*
* print the file header
@ -3088,9 +3083,7 @@ static int proc_task_getattr(struct vfsmount *mnt, struct dentry *dentry, struct
generic_fillattr(inode, stat);
if (p) {
rcu_read_lock();
stat->nlink += get_nr_threads(p);
rcu_read_unlock();
put_task_struct(p);
}

2
kernel/sched_debug.c
View File

@ -333,12 +333,10 @@ void proc_sched_show_task(struct task_struct *p, struct seq_file *m)
unsigned long flags;
int num_threads = 1;
rcu_read_lock();
if (lock_task_sighand(p, &flags)) {
num_threads = atomic_read(&p->signal->count);
unlock_task_sighand(p, &flags);
}
rcu_read_unlock();
SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, p->pid, num_threads);
SEQ_printf(m,