[Cluster-devel] [PATCH] gfs2: Add check for mempool_alloc

[Cluster-devel] [PATCH] gfs2: Add check for mempool_alloc

[Jiasheng Jiang]

As the potential failure of mempool_alloc(),
it could return NULL pointer.
Therefore, it should be better to check it
in order to avoid the dereference of the NULL
pointer.

Fixes: e8c92ed76900 ("GFS2: Clean up log write code path")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
---
 fs/gfs2/log.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index f0ee3ff6f9a8..10dd09e9b0e4 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -837,6 +837,9 @@ void gfs2_write_log_header(struct gfs2_sbd *sdp, struct gfs2_jdesc *jd,
 		return;
 
 	page = mempool_alloc(gfs2_page_pool, GFP_NOIO);
+	if (!page)
+		return;
+
 	lh = page_address(page);
 	clear_page(lh);
 
-- 
2.25.1

[Cluster-devel] [PATCH] gfs2: Add check for mempool_alloc

[Christoph Hellwig]

On Fri, Mar 11, 2022 at 04:36:16PM +0800, Jiasheng Jiang wrote:
> As the potential failure of mempool_alloc(),
> it could return NULL pointer.
> Therefore, it should be better to check it
> in order to avoid the dereference of the NULL
> pointer.
> 
> Fixes: e8c92ed76900 ("GFS2: Clean up log write code path")
> Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>

Please explain how it could fail to start with.

[Cluster-devel] [PATCH] gfs2: Add check for mempool_alloc

[Jiasheng Jiang]

On Wed, 30 Mar 2022 11:56:41 +0800 Christoph Hellwig wrote:
>> As the potential failure of mempool_alloc(),
>> it could return NULL pointer.
>> Therefore, it should be better to check it
>> in order to avoid the dereference of the NULL
>> pointer.
>> 
>> Fixes: e8c92ed76900 ("GFS2: Clean up log write code path")
>> Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
> 
> Please explain how it could fail to start with.

I think that for safety, the cost of redundant and harmless
check is acceptable.
Also, checking after allocation is a good program pattern.
Therefore, it should be better to check it although it is
hard to fail.

Thanks,
Jiang

[Cluster-devel] [PATCH] gfs2: Add check for mempool_alloc

[Christoph Hellwig]

On Fri, Apr 01, 2022 at 11:37:55AM +0800, Jiasheng Jiang wrote:
> >> Fixes: e8c92ed76900 ("GFS2: Clean up log write code path")
> >> Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
> > 
> > Please explain how it could fail to start with.
> 
> I think that for safety, the cost of redundant and harmless
> check is acceptable.
> Also, checking after allocation is a good program pattern.
> Therefore, it should be better to check it although it is
> hard to fail.

Please take a look at the implemetation and documentation of
mempool_alloc again.  Thewhole point of that function is that it will
not fail for allocations that can sleep.