linux-kernel - [PATCH 3.2 128/149] Revert "zram: use zram->lock to protect zram_free

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Date:	Mon, 21 Oct 2013 09:46:28 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org
Subject: [PATCH 3.2 128/149] Revert "zram: use zram->lock to protect
 zram_free_page() in swap free notify path"

3.2.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Hutchings <ben@...adent.org.uk>

This reverts commit 9e443904906ca2b5b3ae71f34ac4a4fa6905623e, which
was commit 57ab048532c0d975538cebd4456491b5c34248f4 upstream.

Taking the semaphore here leads to sleeping in atomic context.  This
was fixed in mainline commit a0c516cbfc74 ("zram: don't grab mutex in
zram_slot_free_noity") but that is too difficult to backport.

Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -709,9 +709,7 @@ static void zram_slot_free_notify(struct
 	struct zram *zram;
 
 	zram = bdev->bd_disk->private_data;
-	down_write(&zram->lock);
 	zram_free_page(zram, index);
-	up_write(&zram->lock);
 	zram_stat64_inc(zram, &zram->stats.notify_free);
 }
 
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -107,9 +107,8 @@ struct zram {
 	void *compress_buffer;
 	struct table *table;
 	spinlock_t stat64_lock;	/* protect 64-bit stats */
-	struct rw_semaphore lock; /* protect compression buffers, table,
-				   * 32bit stat counters against concurrent
-				   * notifications, reads and writes */
+	struct rw_semaphore lock; /* protect compression buffers and table
+				   * against concurrent read and writes */
 	struct request_queue *queue;
 	struct gendisk *disk;
 	int init_done;

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