The patch titled
signal, procfs: lock_task_sighand() do not need rcu_read_lock()
has been removed from the -mm tree. Its filename was
signal-procfs-lock_task_sighand-do-not-need-rcu_read_lock.patch
This patch was dropped because it was merged into mainline or a subsystem tree
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: signal, procfs: lock_task_sighand() do not need rcu_read_lock()
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/array.c | 2 --
fs/proc/base.c | 9 +--------
kernel/sched_debug.c | 2 --
3 files changed, 1 insertion(+), 12 deletions(-)
diff -puN fs/proc/array.c~signal-procfs-lock_task_sighand-do-not-need-rcu_read_lock fs/proc/array.c
--- a/fs/proc/array.c~signal-procfs-lock_task_sighand-do-not-need-rcu_read_lock
+++ a/fs/proc/array.c
@@ -261,7 +261,6 @@ static inline void task_sig(struct seq_f
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_f
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);
diff -puN fs/proc/base.c~signal-procfs-lock_task_sighand-do-not-need-rcu_read_lock fs/proc/base.c
--- a/fs/proc/base.c~signal-procfs-lock_task_sighand-do-not-need-rcu_read_lock
+++ a/fs/proc/base.c
@@ -164,7 +164,6 @@ static struct fs_struct *get_fs_struct(s
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_s
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 vfsm
generic_fillattr(inode, stat);
if (p) {
- rcu_read_lock();
stat->nlink += get_nr_threads(p);
- rcu_read_unlock();
put_task_struct(p);
}
diff -puN kernel/sched_debug.c~signal-procfs-lock_task_sighand-do-not-need-rcu_read_lock kernel/sched_debug.c
--- a/kernel/sched_debug.c~signal-procfs-lock_task_sighand-do-not-need-rcu_read_lock
+++ a/kernel/sched_debug.c
@@ -333,12 +333,10 @@ void proc_sched_show_task(struct task_st
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,
_
Patches currently in -mm which might be from laijs@xxxxxxxxxxxxxx are
origin.patch
cgroups-fix-probable-race-with-put_css_set-and-find_css_set.patch
cgroups-fix-probable-race-with-put_css_set-and-find_css_set-fix.patch
cgroups-fix-probable-race-with-put_css_set-and-find_css_set-cgroups-eliminate-race-in-css_set-refcounting.patch
cgroups-convert-tasks-file-to-use-a-seq_file-with-shared-pid-array.patch
devcgroup-remove-spin_lock.patch
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