Commit 37c54f9b authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Linus Torvalds
Browse files

kernel: set USER_DS in kthread_use_mm 



Some architectures like arm64 and s390 require USER_DS to be set for
kernel threads to access user address space, which is the whole purpose of
kthread_use_mm, but other like x86 don't.  That has lead to a huge mess
where some callers are fixed up once they are tested on said
architectures, while others linger around and yet other like io_uring try
to do "clever" optimizations for what usually is just a trivial asignment
to a member in the thread_struct for most architectures.

Make kthread_use_mm set USER_DS, and kthread_unuse_mm restore to the
previous value instead.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Tested-by: default avatarJens Axboe <axboe@kernel.dk>
Reviewed-by: default avatarJens Axboe <axboe@kernel.dk>
Acked-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: http://lkml.kernel.org/r/20200404094101.672954-7-hch@lst.de


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f5678e7f

drivers/usb/gadget/function/f_fs.c

+0 −4
Original line number Diff line number Diff line
@@ -824,13 +824,9 @@ static void ffs_user_copy_worker(struct work_struct *work) 
	bool kiocb_has_eventfd = io_data->kiocb->ki_flags & IOCB_EVENTFD;



	if (io_data->read && ret > 0) {

		mm_segment_t oldfs = get_fs();



		set_fs(USER_DS);

		kthread_use_mm(io_data->mm);

		ret = ffs_copy_to_iter(io_data->buf, ret, &io_data->data);

		kthread_unuse_mm(io_data->mm);

		set_fs(oldfs);

	}



	io_data->kiocb->ki_complete(io_data->kiocb, ret, ret);

drivers/vhost/vhost.c

+0 −3
Original line number Diff line number Diff line
@@ -329,9 +329,7 @@ static int vhost_worker(void *data) 
	struct vhost_dev *dev = data;

	struct vhost_work *work, *work_next;

	struct llist_node *node;

	mm_segment_t oldfs = get_fs();



	set_fs(USER_DS);

	kthread_use_mm(dev->mm);



	for (;;) {
@@ -361,7 +359,6 @@ static int vhost_worker(void *data) 
		}

	}

	kthread_unuse_mm(dev->mm);

	set_fs(oldfs);

	return 0;

}

fs/io-wq.c

+2 −6
Original line number Diff line number Diff line
@@ -169,7 +169,6 @@ static bool __io_worker_unuse(struct io_wqe *wqe, struct io_worker *worker) 
			dropped_lock = true;

		}

		__set_current_state(TASK_RUNNING);

		set_fs(KERNEL_DS);

		kthread_unuse_mm(worker->mm);

		mmput(worker->mm);

		worker->mm = NULL;
@@ -421,14 +420,11 @@ static void io_wq_switch_mm(struct io_worker *worker, struct io_wq_work *work) 
		mmput(worker->mm);

		worker->mm = NULL;

	}

	if (!work->mm) {

		set_fs(KERNEL_DS);

	if (!work->mm)

		return;

	}



	if (mmget_not_zero(work->mm)) {

		kthread_use_mm(work->mm);

		if (!worker->mm)

			set_fs(USER_DS);

		worker->mm = work->mm;

		/* hang on to this mm */

		work->mm = NULL;

fs/io_uring.c

+0 −4
Original line number Diff line number Diff line
@@ -5989,15 +5989,12 @@ static int io_sq_thread(void *data) 
{

	struct io_ring_ctx *ctx = data;

	const struct cred *old_cred;

	mm_segment_t old_fs;

	DEFINE_WAIT(wait);

	unsigned long timeout;

	int ret = 0;



	complete(&ctx->sq_thread_comp);



	old_fs = get_fs();

	set_fs(USER_DS);

	old_cred = override_creds(ctx->creds);



	timeout = jiffies + ctx->sq_thread_idle;
@@ -6102,7 +6099,6 @@ static int io_sq_thread(void *data) 
	if (current->task_works)

		task_work_run();



	set_fs(old_fs);

	io_sq_thread_drop_mm(ctx);

	revert_creds(old_cred);

kernel/kthread.c

+6 −0
Original line number Diff line number Diff line
@@ -52,6 +52,7 @@ struct kthread { 
	unsigned long flags;

	unsigned int cpu;

	void *data;

	mm_segment_t oldfs;

	struct completion parked;

	struct completion exited;

#ifdef CONFIG_BLK_CGROUP
@@ -1235,6 +1236,9 @@ void kthread_use_mm(struct mm_struct *mm) 


	if (active_mm != mm)

		mmdrop(active_mm);



	to_kthread(tsk)->oldfs = get_fs();

	set_fs(USER_DS);

}

EXPORT_SYMBOL_GPL(kthread_use_mm);
@@ -1249,6 +1253,8 @@ void kthread_unuse_mm(struct mm_struct *mm) 
	WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));

	WARN_ON_ONCE(!tsk->mm);



	set_fs(to_kthread(tsk)->oldfs);



	task_lock(tsk);

	sync_mm_rss(mm);

	tsk->mm = NULL;

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