[PATCH net] net: ibm: emac: mal: fix potential system hang in mal_remove()

[PATCH net] net: ibm: emac: mal: fix potential system hang in mal_remove()

[Rosen Penev]

napi_disable() is not idempotent and calling it on an already-disabled
or unenabled NAPI context will cause the kernel to spin indefinitely
waiting for the NAPI_STATE_SCHED bit to clear.

In mal_remove(), napi_disable() is called unconditionally. If no MACs were
registered, NAPI was never enabled. Also, if they were registered but
subsequently unregistered, NAPI was already disabled in
mal_unregister_commac(). In either case, calling napi_disable() causes
the kernel to hang upon module removal.

Fix this by only calling napi_disable() in mal_remove() if the commac list
is not empty (which implies NAPI is enabled).

Fixes: 59e90b2d2250 ("ibm_emac: Convert to use napi_struct independent of struct net_device")
Assisted-by: antigravity:gemini-3.5-flash
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 drivers/net/ethernet/ibm/emac/mal.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/ibm/emac/mal.c b/drivers/net/ethernet/ibm/emac/mal.c
index 83dd7f99d8d5..74526002d52b 100644
--- a/drivers/net/ethernet/ibm/emac/mal.c
+++ b/drivers/net/ethernet/ibm/emac/mal.c
@@ -712,13 +712,13 @@ static void mal_remove(struct platform_device *ofdev)
 	MAL_DBG(mal, "remove" NL);

 	/* Synchronize with scheduled polling */
-	napi_disable(&mal->napi);
-
-	if (!list_empty(&mal->list))
+	if (!list_empty(&mal->list)) {
+		napi_disable(&mal->napi);
 		/* This is *very* bad */
 		WARN(1, KERN_EMERG
 		       "mal%d: commac list is not empty on remove!\n",
 		       mal->index);
+	}

 	mal_reset(mal);

--
2.54.0