[ndctl PATCH 3/3] libndctl: check for active system-ram before disabling daxctl devices

From: Vishal Verma <vishal.l.verma@intel.com>
To: <linux-nvdimm@lists.01.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
	Chunye Xu <chunye.xu@intel.com>
Subject: [ndctl PATCH 3/3] libndctl: check for active system-ram before disabling daxctl devices
Date: Tue, 30 Mar 2021 21:12:29 -0600	[thread overview]
Message-ID: <20210331031229.384068-4-vishal.l.verma@intel.com> (raw)
In-Reply-To: <20210331031229.384068-1-vishal.l.verma@intel.com>

Teach ndctl_namespace_disable_safe() to look at the state of a
daxctl_dev with respect to whether it is active in 'system-ram' mode
before disabling it. This is similar to checking whether a filesystem is
actively mounted on a namespace before disabling it.

Without this, libndctl would happily disable a devdax namespace while the
device was active in system-ram mode. If the namespace was subsequently
also destroyed, this would leave the memory without any sort of a
'handle' to perform any subsequent operation on it, and the system would
have to be rebooted to get out of this situation.

Reported-by: Chunye Xu <chunye.xu@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
 ndctl/lib/libndctl.c   | 25 ++++++++++++++++++++++++-
 test/daxctl-devices.sh | 16 ++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/ndctl/lib/libndctl.c b/ndctl/lib/libndctl.c
index 2f6d806..2eda56c 100644
--- a/ndctl/lib/libndctl.c
+++ b/ndctl/lib/libndctl.c
@@ -4593,21 +4593,40 @@ NDCTL_EXPORT int ndctl_namespace_disable_invalidate(struct ndctl_namespace *ndns
 	return ndctl_namespace_disable(ndns);
 }
 
+static int ndctl_dax_has_active_memory(struct ndctl_dax *dax)
+{
+	struct daxctl_region *dax_region;
+	struct daxctl_dev *dax_dev;
+
+	dax_region = ndctl_dax_get_daxctl_region(dax);
+	if (!dax_region)
+		return 0;
+
+	daxctl_dev_foreach(dax_region, dax_dev)
+		if (daxctl_dev_has_online_memory(dax_dev))
+			return 1;
+
+	return 0;
+}
+
 NDCTL_EXPORT int ndctl_namespace_disable_safe(struct ndctl_namespace *ndns)
 {
 	const char *devname = ndctl_namespace_get_devname(ndns);
 	struct ndctl_ctx *ctx = ndctl_namespace_get_ctx(ndns);
 	struct ndctl_pfn *pfn = ndctl_namespace_get_pfn(ndns);
 	struct ndctl_btt *btt = ndctl_namespace_get_btt(ndns);
+	struct ndctl_dax *dax = ndctl_namespace_get_dax(ndns);
 	const char *bdev = NULL;
+	int fd, active = 0;
 	char path[50];
-	int fd;
 	unsigned long long size = ndctl_namespace_get_size(ndns);
 
 	if (pfn && ndctl_pfn_is_enabled(pfn))
 		bdev = ndctl_pfn_get_block_device(pfn);
 	else if (btt && ndctl_btt_is_enabled(btt))
 		bdev = ndctl_btt_get_block_device(btt);
+	else if (dax && ndctl_dax_is_enabled(dax))
+		active = ndctl_dax_has_active_memory(dax);
 	else if (ndctl_namespace_is_enabled(ndns))
 		bdev = ndctl_namespace_get_block_device(ndns);
 
@@ -4632,6 +4651,10 @@ NDCTL_EXPORT int ndctl_namespace_disable_safe(struct ndctl_namespace *ndns)
 					devname, bdev, strerror(errno));
 			return -errno;
 		}
+	} else if (active) {
+		dbg(ctx, "%s: active as system-ram, refusing to disable\n",
+				devname);
+		return -EBUSY;
 	} else {
 		if (size == 0)
 			/* No disable necessary due to no capacity allocated */
diff --git a/test/daxctl-devices.sh b/test/daxctl-devices.sh
index eed5906..56c9691 100755
--- a/test/daxctl-devices.sh
+++ b/test/daxctl-devices.sh
@@ -105,6 +105,22 @@ daxctl_test()
 	"$DAXCTL" reconfigure-device -f -m devdax "$daxdev"
 	[[ $(daxctl_get_mode "$daxdev") == "devdax" ]]
 
+	# fail 'ndctl-disable-namespace' while the devdax namespace is active
+	# as system-ram. If this test fails, a reboot will be required to
+	# recover from the resulting state.
+	test -n "$testdev"
+	"$DAXCTL" reconfigure-device -m system-ram "$daxdev"
+	[[ $(daxctl_get_mode "$daxdev") == "system-ram" ]]
+	if ! "$NDCTL" disable-namespace "$testdev"; then
+		echo "disable-namespace failed as expected"
+	else
+		echo "disable-namespace succeded, expected failure"
+		echo "reboot required to recover from this state"
+		return 1
+	fi
+	"$DAXCTL" reconfigure-device -f -m devdax "$daxdev"
+	[[ $(daxctl_get_mode "$daxdev") == "devdax" ]]
+
 	# this tests for reconfiguration failure if an online-policy is set
 	set_online_policy
 	: "This command is expected to fail:"
-- 
2.30.2
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