kthread: Generalize pf_io_worker so it can point to struct kthread

The point of using set_child_tid to hold the kthread pointer was that
it already did what is necessary.  There are now restrictions on when
set_child_tid can be initialized and when set_child_tid can be used in
schedule_tail.  Which indicates that continuing to use set_child_tid
to hold the kthread pointer is a bad idea.

Instead of continuing to use the set_child_tid field of task_struct
generalize the pf_io_worker field of task_struct and use it to hold
the kthread pointer.

Rename pf_io_worker (which is a void * pointer) to worker_private so
it can be used to store kthreads struct kthread pointer.  Update the
kthread code to store the kthread pointer in the worker_private field.
Remove the places where set_child_tid had to be dealt with carefully
because kthreads also used it.

Link: https://lkml.kernel.org/r/CAHk-=wgtFAA9SbVYg0gR1tqPMC17-NYcs0GQkaYg1bGhh1uJQQ@mail.gmail.com
Link: https://lkml.kernel.org/r/87a6grvqy8.fsf_-_@email.froward.int.ebiederm.org
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/fs/io-wq.c b/fs/io-wq.c
index 88202de..e4fc738 100644 (file)
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -657,7 +657,7 @@ loop:
  */
 void io_wq_worker_running(struct task_struct *tsk)
 {
-       struct io_worker *worker = tsk->pf_io_worker;
+       struct io_worker *worker = tsk->worker_private;
 
        if (!worker)
                return;
@@ -675,7 +675,7 @@ void io_wq_worker_running(struct task_struct *tsk)
  */
 void io_wq_worker_sleeping(struct task_struct *tsk)
 {
-       struct io_worker *worker = tsk->pf_io_worker;
+       struct io_worker *worker = tsk->worker_private;
 
        if (!worker)
                return;
@@ -694,7 +694,7 @@ void io_wq_worker_sleeping(struct task_struct *tsk)
 static void io_init_new_worker(struct io_wqe *wqe, struct io_worker *worker,
                               struct task_struct *tsk)
 {
-       tsk->pf_io_worker = worker;
+       tsk->worker_private = worker;
        worker->task = tsk;
        set_cpus_allowed_ptr(tsk, wqe->cpu_mask);
        tsk->flags |= PF_NO_SETAFFINITY;

diff --git a/fs/io-wq.h b/fs/io-wq.h
index 41bf376..c7c2394 100644 (file)
--- a/fs/io-wq.h
+++ b/fs/io-wq.h
@@ -200,6 +200,6 @@ static inline void io_wq_worker_running(struct task_struct *tsk)
 static inline bool io_wq_current_is_worker(void)
 {
        return in_task() && (current->flags & PF_IO_WORKER) &&
-               current->pf_io_worker;
+               current->worker_private;
 }
 #endif

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 78c351e..52f2fdf 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -987,8 +987,8 @@ struct task_struct {
        /* CLONE_CHILD_CLEARTID: */
        int __user                      *clear_child_tid;
 
-       /* PF_IO_WORKER */
-       void                            *pf_io_worker;
+       /* PF_KTHREAD | PF_IO_WORKER */
+       void                            *worker_private;
 
        u64                             utime;
        u64                             stime;

diff --git a/kernel/fork.c b/kernel/fork.c
index 0816be1..6f0293c 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -950,7 +950,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
        tsk->splice_pipe = NULL;
        tsk->task_frag.page = NULL;
        tsk->wake_q.next = NULL;
-       tsk->pf_io_worker = NULL;
+       tsk->worker_private = NULL;
 
        account_kernel_stack(tsk, 1);
 
@@ -2032,12 +2032,6 @@ static __latent_entropy struct task_struct *copy_process(
                siginitsetinv(&p->blocked, sigmask(SIGKILL)|sigmask(SIGSTOP));
        }
 
-       /*
-        * This _must_ happen before we call free_task(), i.e. before we jump
-        * to any of the bad_fork_* labels. This is to avoid freeing
-        * p->set_child_tid which is (ab)used as a kthread's data pointer for
-        * kernel threads (PF_KTHREAD).
-        */
        p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? args->child_tid : NULL;
        /*
         * Clear TID on mm_release()?

diff --git a/kernel/kthread.c b/kernel/kthread.c
index c14707d..261a3c3 100644 (file)
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -72,7 +72,7 @@ enum KTHREAD_BITS {
 static inline struct kthread *to_kthread(struct task_struct *k)
 {
        WARN_ON(!(k->flags & PF_KTHREAD));
-       return (__force void *)k->set_child_tid;
+       return k->worker_private;
 }
 
 /*
@@ -80,7 +80,7 @@ static inline struct kthread *to_kthread(struct task_struct *k)
  *
  * Per construction; when:
  *
- *   (p->flags & PF_KTHREAD) && p->set_child_tid
+ *   (p->flags & PF_KTHREAD) && p->worker_private
  *
  * the task is both a kthread and struct kthread is persistent. However
  * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and
@@ -88,7 +88,7 @@ static inline struct kthread *to_kthread(struct task_struct *k)
  */
 static inline struct kthread *__to_kthread(struct task_struct *p)
 {
-       void *kthread = (__force void *)p->set_child_tid;
+       void *kthread = p->worker_private;
        if (kthread && !(p->flags & PF_KTHREAD))
                kthread = NULL;
        return kthread;
@@ -109,11 +109,7 @@ bool set_kthread_struct(struct task_struct *p)
        init_completion(&kthread->parked);
        p->vfork_done = &kthread->exited;
 
-       /*
-        * We abuse ->set_child_tid to avoid the new member and because it
-        * can't be wrongly copied by copy_process().
-        */
-       p->set_child_tid = (__force void __user *)kthread;
+       p->worker_private = kthread;
        return true;
 }
 
@@ -128,7 +124,7 @@ void free_kthread_struct(struct task_struct *k)
 #ifdef CONFIG_BLK_CGROUP
        WARN_ON_ONCE(kthread && kthread->blkcg_css);
 #endif
-       k->set_child_tid = (__force void __user *)NULL;
+       k->worker_private = NULL;
        kfree(kthread);
 }
 

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d8adbea..ee222b8 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4908,7 +4908,7 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev)
        finish_task_switch(prev);
        preempt_enable();
 
-       if (!(current->flags & PF_KTHREAD) && current->set_child_tid)
+       if (current->set_child_tid)
                put_user(task_pid_vnr(current), current->set_child_tid);
 
        calculate_sigpending();