ndctl/scrub: Reread scrub-engine status at start

BZ: 

Brew: 

commit 4e646fa490ba4b782afa188dd8818b94c419924e

Author: Dan Williams <dan.j.williams@intel.com>

Date:   Wed May 26 16:33:10 2021 -0700

    ndctl/scrub: Reread scrub-engine status at start

    Given that the kernel has exponential backoff to cover the lack of

    interrupts for scrub completion status there is a reasonable likelihood

    that 'ndctl start-scrub' is issued while the hardware/platform scrub-state

    is idle, but the kernel engine poll timer has not fired.

    Trigger at least one poll cycle for the kernel to re-read the scrub-state

    before reporting that ARS is busy.

    Link: https://lore.kernel.org/r/162207199057.3715490.2469820075085914776.stgit@dwillia2-desk3.amr.corp.intel.com

    Reported-by: Krzysztof Rusocki <krzysztof.rusocki@intel.com>

    Signed-off-by: Dan Williams <dan.j.williams@intel.com>

    Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>

diff --git a/ndctl/lib/libndctl.c b/ndctl/lib/libndctl.c

index e5641fe..536e142 100644

--- a/ndctl/lib/libndctl.c

+++ b/ndctl/lib/libndctl.c

@@ -1354,8 +1354,18 @@ static int __ndctl_bus_get_scrub_state(struct ndctl_bus *bus,

 NDCTL_EXPORT int ndctl_bus_start_scrub(struct ndctl_bus *bus)

 {

 	struct ndctl_ctx *ctx = ndctl_bus_get_ctx(bus);

+	int rc;

+

+	rc = sysfs_write_attr(ctx, bus->scrub_path, "1\n");

-	return sysfs_write_attr(ctx, bus->scrub_path, "1\n");

+	/*

+	 * Try at least 1 poll cycle before reporting busy in case this

+	 * request hits the kernel's exponential backoff while the

+	 * hardware/platform scrub state is idle.

+	 */

+	if (rc == -EBUSY && ndctl_bus_poll_scrub_completion(bus, 1, 1) == 0)

+		return sysfs_write_attr(ctx, bus->scrub_path, "1\n");

+	return rc;

 }

 NDCTL_EXPORT int ndctl_bus_get_scrub_state(struct ndctl_bus *bus)