linux-kernel - [PATCH] staging: ion: WARN when the handle kmap

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Date:	Thu, 22 May 2014 17:51:21 -0700
From:	Mitchel Humpherys <mitchelh@...eaurora.org>
To:	linux-mm@...ck.org, Colin Cross <ccross@...roid.com>,
	John Stultz <john.stultz@...aro.org>
Cc:	Android Kernel Team <kernel-team@...roid.com>,
	linux-kernel@...r.kernel.org,
	Mitchel Humpherys <mitchelh@...eaurora.org>
Subject: [PATCH] staging: ion: WARN when the handle kmap_cnt is going to wrap around

There are certain client bugs (double unmap, for example) that can cause
the handle->kmap_cnt (an unsigned int) to wrap around from zero. This
causes problems when the handle is destroyed because we have:

        while (handle->kmap_cnt)
                ion_handle_kmap_put(handle);

which takes a long time to complete when kmap_cnt starts at ~0 and can
result in a watchdog timeout.

WARN and bail when kmap_cnt is about to wrap around from zero.

Signed-off-by: Mitchel Humpherys <mitchelh@...eaurora.org>
---
 drivers/staging/android/ion/ion.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index 3d5bf14722..f55f61a4cc 100644
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -626,6 +626,10 @@ static void ion_handle_kmap_put(struct ion_handle *handle)
 {
 	struct ion_buffer *buffer = handle->buffer;
 
+	if (!handle->kmap_cnt) {
+		WARN(1, "%s: Double unmap detected! bailing...\n", __func__);
+		return;
+	}
 	handle->kmap_cnt--;
 	if (!handle->kmap_cnt)
 		ion_buffer_kmap_put(buffer);
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
hosted by The Linux Foundation

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