linux-kernel - [PATCH] habanalabs: prevent CPU soft lockup on Palladium

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Message-Id: <20190401174430.15553-1-oded.gabbay@gmail.com>
Date:   Mon,  1 Apr 2019 20:44:30 +0300
From:   Oded Gabbay <oded.gabbay@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     gregkh@...uxfoundation.org
Subject: [PATCH] habanalabs: prevent CPU soft lockup on Palladium

Unmapping ptes in the device MMU on Palladium can take a long time, which
can cause a kernel BUG of CPU soft lockup.

This patch minimize the chances for this bug by sleeping a little between
unmapping ptes.

Signed-off-by: Oded Gabbay <oded.gabbay@...il.com>
---
 drivers/misc/habanalabs/memory.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/habanalabs/memory.c b/drivers/misc/habanalabs/memory.c
index 39788b1cf8d0..e9e163545584 100644
--- a/drivers/misc/habanalabs/memory.c
+++ b/drivers/misc/habanalabs/memory.c
@@ -1046,10 +1046,17 @@ static int unmap_device_va(struct hl_ctx *ctx, u64 vaddr)
 
 	mutex_lock(&ctx->mmu_lock);
 
-	for (i = 0 ; i < phys_pg_pack->npages ; i++, next_vaddr += page_size)
+	for (i = 0 ; i < phys_pg_pack->npages ; i++, next_vaddr += page_size) {
 		if (hl_mmu_unmap(ctx, next_vaddr, page_size))
 			dev_warn_ratelimited(hdev->dev,
-				"unmap failed for vaddr: 0x%llx\n", next_vaddr);
+			"unmap failed for vaddr: 0x%llx\n", next_vaddr);
+
+		/* unmapping on Palladium can be really long, so avoid a CPU
+		 * soft lockup bug by sleeping a little between unmapping pages
+		 */
+		if (hdev->pldm)
+			usleep_range(500, 1000);
+	}
 
 	hdev->asic_funcs->mmu_invalidate_cache(hdev, true);
 
-- 
2.17.1