Patch "nvmet: fix ns enable/disable possible hang" has been added to the 6.9-stable tree

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This is a note to let you know that I've just added the patch titled

    nvmet: fix ns enable/disable possible hang

to the 6.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     nvmet-fix-ns-enable-disable-possible-hang.patch
and it can be found in the queue-6.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit e8177c68e3f56c19670d170e9aacd1054402e315
Author: Sagi Grimberg <sagi@xxxxxxxxxxx>
Date:   Tue May 21 23:20:28 2024 +0300

    nvmet: fix ns enable/disable possible hang
    
    [ Upstream commit f97914e35fd98b2b18fb8a092e0a0799f73afdfe ]
    
    When disabling an nvmet namespace, there is a period where the
    subsys->lock is released, as the ns disable waits for backend IO to
    complete, and the ns percpu ref to be properly killed. The original
    intent was to avoid taking the subsystem lock for a prolong period as
    other processes may need to acquire it (for example new incoming
    connections).
    
    However, it opens up a window where another process may come in and
    enable the ns, (re)intiailizing the ns percpu_ref, causing the disable
    sequence to hang.
    
    Solve this by taking the global nvmet_config_sem over the entire configfs
    enable/disable sequence.
    
    Fixes: a07b4970f464 ("nvmet: add a generic NVMe target")
    Signed-off-by: Sagi Grimberg <sagi@xxxxxxxxxxx>
    Reviewed-by: Christoph Hellwig <hch@xxxxxx>
    Reviewed-by: Chaitanya Kulkarni <kch@xxxxxxxxxx>
    Signed-off-by: Keith Busch <kbusch@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/nvme/target/configfs.c b/drivers/nvme/target/configfs.c
index 7fda69395c1ef..dfdff6aba6953 100644
--- a/drivers/nvme/target/configfs.c
+++ b/drivers/nvme/target/configfs.c
@@ -676,10 +676,18 @@ static ssize_t nvmet_ns_enable_store(struct config_item *item,
 	if (kstrtobool(page, &enable))
 		return -EINVAL;
 
+	/*
+	 * take a global nvmet_config_sem because the disable routine has a
+	 * window where it releases the subsys-lock, giving a chance to
+	 * a parallel enable to concurrently execute causing the disable to
+	 * have a misaccounting of the ns percpu_ref.
+	 */
+	down_write(&nvmet_config_sem);
 	if (enable)
 		ret = nvmet_ns_enable(ns);
 	else
 		nvmet_ns_disable(ns);
+	up_write(&nvmet_config_sem);
 
 	return ret ? ret : count;
 }




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