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From:   Jens Axboe <axboe@kernel.dk>
To:     io-uring@vger.kernel.org
Cc:     torvalds@linux-foundation.org, ebiederm@xmission.com,
        metze@samba.org, oleg@redhat.com, linux-kernel@vger.kernel.org,
        Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 3/7] kernel: stop masking signals in create_io_thread()
Date:   Fri, 26 Mar 2021 09:51:17 -0600
Message-Id: <20210326155128.1057078-5-axboe@kernel.dk>
In-Reply-To: <20210326155128.1057078-1-axboe@kernel.dk>
References: <20210326155128.1057078-1-axboe@kernel.dk>
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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 <oleg@redhat.com>
Signed-off-by: Jens Axboe <axboe@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