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[PATCH 3/3] dio: add a mempool for the unaligned block structures

To: linux-fsdevel@xxxxxxxxxxxxxxx
Subject: [PATCH 3/3] dio: add a mempool for the unaligned block structures
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 3 Aug 2010 17:23:24 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1280820204-1418-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1280820204-1418-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

We need the zero block tracking structure allocation to succeed.
Silently failing and potentially allowing data corruption is not an
option. Add a mempool to ensure this allocation will always succeed.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
 fs/direct-io.c |   14 +++++++++++---
 1 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 368abec..dfc5d9a 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -161,12 +161,22 @@ struct dio_zero_block_head {
 static struct dio_zero_block_head dio_zero_blocks[DIO_ZERO_BLOCK_NR];
 #define to_dio_zero_head(zb)   (&dio_zero_blocks[zb % DIO_ZERO_BLOCK_NR])
 
+/* a small mempool just to guarantee progress. */
+#define DIO_ZERO_BLOCK_ENTRIES 2
+static mempool_t *dio_zero_block_pool;
+
 
 static int __init
 dio_init_zero_block(void)
 {
        int i;
 
+       dio_zero_block_pool = mempool_create_kmalloc_pool(
+                                       DIO_ZERO_BLOCK_ENTRIES,
+                                       sizeof(struct dio_zero_block));
+       if (!dio_zero_block_pool)
+               panic("dio: can't create zero block pool");
+
        for (i = 0; i < DIO_ZERO_BLOCK_NR; i++) {
                spin_lock_init(&dio_zero_blocks[i].lock);
                INIT_LIST_HEAD(&dio_zero_blocks[i].list);
@@ -184,9 +194,7 @@ dio_start_zero_block(struct dio *dio, sector_t zero_block)
        struct dio_zero_block_head *zbh = to_dio_zero_head(zero_block);
        struct dio_zero_block *zb;
 
-       zb = kmalloc(sizeof(*zb), GFP_NOIO);
-       if (!zb)
-               return;
+       zb = mempool_alloc(dio_zero_block_pool, GFP_NOIO);
        INIT_LIST_HEAD(&zb->dio_list);
        init_waitqueue_head(&zb->wq);
        zb->zero_block = zero_block;
-- 
1.7.1

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