Subject: [PATCH -next] ashmem: Fix ashmem_shrink deadlock.

From: Robert Love <[email-masked]>
Date: Wed, 1 May 2013 09:56:13 -0400

Don't acquire ashmem_mutex in ashmem_shrink if we've somehow recursed into the
shrinker code from within ashmem. Just bail out, avoiding a deadlock. This is
fine, as ashmem cache pruning is advisory anyhow.

Signed-off-by: Robert Love <[email-masked]>
---
 drivers/staging/android/ashmem.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index e681bdd..82c6768 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -363,7 +363,11 @@ static int ashmem_shrink(struct shrinker *s, struct shrink_control *sc)
 	if (!sc->nr_to_scan)
 		return lru_count;
 
-	mutex_lock(&ashmem_mutex);
+	/* avoid recursing into this code from within ashmem itself */
+	if (!mutex_trylock(&ashmem_mutex)) {
+		return -1;
+	}
+
 	list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) {
 		loff_t start = range->pgstart * PAGE_SIZE;
 		loff_t end = (range->pgend + 1) * PAGE_SIZE;
-- 
1.8.2.1