[PATCH net-next v6 01/12] net/rds: ib: don't enable interrupts in rds_ib_conn_free()

[Allison Henderson <achender@kernel.org>]

rds_ib_conn_free() unlinks the connection from its device or nodev
list under spin_lock_irq()/spin_unlock_irq().  It is not only called
from the rmmod path, though: __rds_conn_create() calls
trans->conn_free() to undo a lost creation race while it still holds
rds_conn_lock, taken with spin_lock_irqsave().  The unconditional
spin_unlock_irq() then re-enables interrupts with rds_conn_lock held
and leaves them enabled when the caller's spin_unlock_irqrestore()
runs, defeating the irqsave the caller relied on.

Use the irqsave/irqrestore pair, as rds_tcp_conn_free() and
rds_loop_conn_free() already do.

Fixes: 745cbccac3fe ("RDS: Rewrite connection cleanup, fixing oops on rmmod")
Assisted-by: Claude-Code:claude-fable-5
Signed-off-by: Allison Henderson <achender@kernel.org>
---
 net/rds/ib_cm.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/rds/ib_cm.c b/net/rds/ib_cm.c
index 6e3110a04ae6..53147793d44b 100644
--- a/net/rds/ib_cm.c
+++ b/net/rds/ib_cm.c
@@ -1271,6 +1271,7 @@ void rds_ib_conn_free(void *arg)
 {
 	struct rds_ib_connection *ic = arg;
 	spinlock_t	*lock_ptr;
+	unsigned long flags;
 
 	rdsdebug("ic %p\n", ic);
 
@@ -1278,12 +1279,16 @@ void rds_ib_conn_free(void *arg)
 	 * Conn is either on a dev's list or on the nodev list.
 	 * A race with shutdown() or connect() would cause problems
 	 * (since rds_ibdev would change) but that should never happen.
+	 *
+	 * Callers may hold rds_conn_lock with interrupts disabled
+	 * (__rds_conn_create() undoing a lost creation race), so do not
+	 * re-enable interrupts unconditionally here.
 	 */
 	lock_ptr = ic->rds_ibdev ? &ic->rds_ibdev->spinlock : &ib_nodev_conns_lock;
 
-	spin_lock_irq(lock_ptr);
+	spin_lock_irqsave(lock_ptr, flags);
 	list_del(&ic->ib_node);
-	spin_unlock_irq(lock_ptr);
+	spin_unlock_irqrestore(lock_ptr, flags);
 
 	rds_ib_recv_free_caches(ic);
 
-- 
2.25.1