[PATCH net 1/3] net/rds: don't use unpin_user_pages_dirty_lock() from atomic context

[Allison Henderson <achender@kernel.org>]

From: Gerd Rausch <gerd.rausch@oracle.com>

rds_rdma_free_op() and rds_atomic_free_op() are reached from the IB
send completion path via

  rds_ib_tasklet_fn_send()
    rds_ib_send_cqe_handler()
      rds_message_put()
        rds_message_purge()
          rds_rdma_free_op() / rds_atomic_free_op()

which runs in tasklet (softirq) context.  Both functions unpin the
user pages of the op with unpin_user_pages_dirty_lock(), which uses
set_page_dirty_lock() and thus may call lock_page() and sleep.
Sleeping in softirq context is not allowed and can deadlock or crash.

Dirty the pages with set_page_dirty() and release them with
unpin_user_page() instead, the same way this code handled the pages
before the conversion to the pin_user_pages API.

This mirrors Oracle UEK commit "net/rds: Avoid
unpin_user_pages_dirty_lock() in tasklets".

Fixes: 0d4597c8c5ab ("net/rds: Track user mapped pages through special API")
Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
[achender: port to net-next; omit UEK's WARN_ON_ONCE(!page->mapping &&
 irqs_disabled()) debug check; update commit message]
Assisted-by: Claude-Code:claude-fable-5
Signed-off-by: Allison Henderson <achender@kernel.org>
---
 net/rds/rdma.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/net/rds/rdma.c b/net/rds/rdma.c
index 61fb6e45281bf..201cbe38fa893 100644
--- a/net/rds/rdma.c
+++ b/net/rds/rdma.c
@@ -495,9 +495,13 @@ void rds_rdma_free_op(struct rm_rdma_op *ro)
 
 			/* Mark page dirty if it was possibly modified, which
 			 * is the case for a RDMA_READ which copies from remote
-			 * to local memory
+			 * to local memory.  This can be called from the IB
+			 * send completion tasklet, so the sleeping _lock
+			 * variant must not be used here.
 			 */
-			unpin_user_pages_dirty_lock(&page, 1, !ro->op_write);
+			if (!ro->op_write)
+				set_page_dirty(page);
+			unpin_user_page(page);
 		}
 	}
 
@@ -513,8 +517,12 @@ void rds_atomic_free_op(struct rm_atomic_op *ao)
 
 	/* Mark page dirty if it was possibly modified, which
 	 * is the case for a RDMA_READ which copies from remote
-	 * to local memory */
-	unpin_user_pages_dirty_lock(&page, 1, true);
+	 * to local memory.  This can be called from the IB send
+	 * completion tasklet, so the sleeping _lock variant must
+	 * not be used here.
+	 */
+	set_page_dirty(page);
+	unpin_user_page(page);
 
 	kfree(ao->op_notifier);
 	ao->op_notifier = NULL;
-- 
2.25.1