[PATCH 3/7] kernel: stop masking signals in create_io_thread()

[Jens Axboe]

This is racy - move the blocking into when the task is created and
we're marking it as PF_IO_WORKER anyway. The IO threads are now
prepared to handle signals like SIGSTOP as well, so clear that from
the mask to allow proper stopping of IO threads.

Reported-by: Oleg Nesterov <o...@redhat.com>
Signed-off-by: Jens Axboe <ax...@kernel.dk>
---
 kernel/fork.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index d3171e8e88e5..ddaa15227071 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1940,8 +1940,14 @@ static __latent_entropy struct task_struct *copy_process(
        p = dup_task_struct(current, node);
        if (!p)
                goto fork_out;
-       if (args->io_thread)
+       if (args->io_thread) {
+               /*
+                * Mark us an IO worker, and block any signal that isn't
+                * fatal or STOP
+                */
                p->flags |= PF_IO_WORKER;
+               siginitsetinv(&p->blocked, sigmask(SIGKILL)|sigmask(SIGSTOP));
+       }
 
        /*
         * This _must_ happen before we call free_task(), i.e. before we jump
@@ -2430,14 +2436,8 @@ struct task_struct *create_io_thread(int (*fn)(void *), 
void *arg, int node)
                .stack_size     = (unsigned long)arg,
                .io_thread      = 1,
        };
-       struct task_struct *tsk;
 
-       tsk = copy_process(NULL, 0, node, &args);
-       if (!IS_ERR(tsk)) {
-               sigfillset(&tsk->blocked);
-               sigdelsetmask(&tsk->blocked, sigmask(SIGKILL));
-       }
-       return tsk;
+       return copy_process(NULL, 0, node, &args);
 }
 
 /*
-- 
2.31.0