Re: [PATCH v2] mm/shmem.c: check the return value of mpol_to_str()

[Chen Gang <gang.chen@asianux.com>]

On 09/13/2013 02:19 AM, KOSAKI Motohiro wrote:
>> BTW: in my opinion, within mpol_to_str(), the VM_BUG_ON() need be
>> replaced by returning -EINVAL.
> 
> Nope. mpol_to_str() is not carefully designed since it was born. It
> doesn't have a way to get proper buffer size. That said, the function
> assume all caller know proper buffer size. So, just adding EINVAL
> doesn't solve anything. we need to add a way to get proper buffer length
> at least if we take your way. However it is overengineering because
> current all caller doesn't need it.
> 


That sounds reasonable.

Hmm... but I still believe there must be a fixing way to satisfy us all.

Please check the patch below whether can satisfy us all, thanks.


-------------------------------patch begin-----------------------------

mm/shmem.c: use VM_BUG_ON() for mpol_to_str() when it fails.

  mpol_to_str() is an extern function which may return a failure. But in
  our case, it should not,

  If it really return a failure, that means current kernel is continuing
  blindly (e.g. some kernel structures are corrupted), should be stopped
  as soon as possible.

Signed-off-by: Chen Gang <gang.chen@asianux.com>
---
 mm/shmem.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 8612a95..3f81120 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -890,7 +890,7 @@ static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
 	if (!mpol || mpol->mode == MPOL_DEFAULT)
 		return;		/* show nothing */
 
-	mpol_to_str(buffer, sizeof(buffer), mpol);
+	VM_BUG_ON(mpol_to_str(buffer, sizeof(buffer), mpol) < 0);
 
 	seq_printf(seq, ",mpol=%s", buffer);
 }
-- 
1.7.7.6

-------------------------------patch end-------------------------------


Thanks.
-- 
Chen Gang

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