linux-kernel - [PATCH] staging: android: ashmem: remove usage of list iterator after the loop body

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Date:   Thu, 31 Mar 2022 23:39:34 +0200
From:   Jakob Koschel <jakobkoschel@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <brauner@...nel.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        linux-kernel@...r.kernel.org, linux-staging@...ts.linux.dev,
        Mike Rapoport <rppt@...nel.org>,
        "Brian Johannesmeyer" <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>, Jakob Koschel <jakobkoschel@...il.com>
Subject: [PATCH] staging: android: ashmem: remove usage of list iterator after the loop body

In preparation to limit the scope of a list iterator to the list
traversal loop, use a dedicated pointer to point to the found element
[1].

Before, the code implicitly used the head when no element was found
when using &pos->list. Since the new variable is only set if an
element was found, the head needs to be used explicitly if the
variable is NULL.

Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
Signed-off-by: Jakob Koschel <jakobkoschel@...il.com>
---
 drivers/staging/android/ashmem.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index ddbde3f8430e..a1e245827cf6 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -703,30 +703,33 @@ static int ashmem_pin(struct ashmem_area *asma, size_t pgstart, size_t pgend,
 static int ashmem_unpin(struct ashmem_area *asma, size_t pgstart, size_t pgend,
 			struct ashmem_range **new_range)
 {
-	struct ashmem_range *range, *next;
+	struct ashmem_range *range = NULL, *iter, *next;
 	unsigned int purged = ASHMEM_NOT_PURGED;
 
 restart:
-	list_for_each_entry_safe(range, next, &asma->unpinned_list, unpinned) {
+	list_for_each_entry_safe(iter, next, &asma->unpinned_list, unpinned) {
 		/* short circuit: this is our insertion point */
-		if (range_before_page(range, pgstart))
+		if (range_before_page(iter, pgstart)) {
+			range = iter;
 			break;
+		}
 
 		/*
 		 * The user can ask us to unpin pages that are already entirely
 		 * or partially pinned. We handle those two cases here.
 		 */
-		if (page_range_subsumed_by_range(range, pgstart, pgend))
+		if (page_range_subsumed_by_range(iter, pgstart, pgend))
 			return 0;
-		if (page_range_in_range(range, pgstart, pgend)) {
-			pgstart = min(range->pgstart, pgstart);
-			pgend = max(range->pgend, pgend);
-			purged |= range->purged;
-			range_del(range);
+		if (page_range_in_range(iter, pgstart, pgend)) {
+			pgstart = min(iter->pgstart, pgstart);
+			pgend = max(iter->pgend, pgend);
+			purged |= iter->purged;
+			range_del(iter);
 			goto restart;
 		}
 	}
 
+	range = list_prepare_entry(range, &asma->unpinned_list, unpinned);
 	range_alloc(asma, range, purged, pgstart, pgend, new_range);
 	return 0;
 }

base-commit: f82da161ea75dc4db21b2499e4b1facd36dab275
-- 
2.25.1