pds_core: yield the CPU while waiting for the adminq to drain

pdsc_adminq_wait_and_dec_once_unused() busy-waits for adminq_refcnt to
drop to one:

	while (!refcount_dec_if_one(&pdsc->adminq_refcnt))
		cpu_relax();

The refcount is held by pdsc_adminq_post() for the duration of an
in-flight command, which can wait up to devcmd_timeout seconds
(PDS_CORE_DEVCMD_TIMEOUT is 5) for the hardware to complete. cpu_relax()
is not a reschedule point, so on a non-preemptible kernel this loop can
spin on the CPU for several seconds, starving other tasks on that core.

Add cond_resched() to the loop so the waiter yields to other runnable
tasks while it polls, keeping cpu_relax() as the busy-wait hint between
checks.

Fixes: 7e82a8745b95 ("pds_core: Prevent race issues involving the adminq")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260629200358.2626129-1-nikhil.rao%40amd.com?part=2
Signed-off-by: Nikhil P. Rao <nikhil.rao@amd.com>
Reviewed-by: Eric Joyner <eric.joyner@amd.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Link: https://patch.msgid.link/20260714201456.1776153-1-nikhil.rao@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ethernet/amd/pds_core/core.c b/drivers/net/ethernet/amd/pds_core/core.c
index e39b2c9beb2093c1e03ba723112831835c379cb7..04ec2569c61c0861d87cc9e3d61f1478e0ba5e27 100644 (file)
--- a/drivers/net/ethernet/amd/pds_core/core.c
+++ b/drivers/net/ethernet/amd/pds_core/core.c
@@ -539,6 +539,7 @@ static void pdsc_adminq_wait_and_dec_once_unused(struct pdsc *pdsc)
                dev_dbg_ratelimited(pdsc->dev, "%s: adminq in use\n",
                                    __func__);
                cpu_relax();
+               cond_resched();
        }
 }