[PATCH] fs, dlm: Don't leak, don't do pointless NULL checks and use kzalloc

[PATCH] fs, dlm: Don't leak, don't do pointless NULL checks and use kzalloc

[Jesper Juhl]

In fs/dlm/lock.c in the dlm_scan_waiters() function there are 3 small
issues:

1) first time through the loop we allocate memory for 'warned', if we
then (in the loop) don't take the "if (!warned)" path and loop again,
the second time through the loop we'll allocate memory again and store
it to 'warned' without freeing the previous allocation - this leaks
memory.
Fix this by kfree'ing 'warned' just before the in-loop allocation. The
first time through the loop this will result in a pointless
kfree(NULL), but that's a small price to pay for avoiding a mem leak
IMHO.

2) There's no need to test the return value of the allocation and do a
memset if is succeedes. Just use kzalloc() to obtain zeroed memory.

3) Since kfree() handles NULL pointers gracefully, the test of
'warned' against NULL before the kfree() after the loop is completely
pointless. Remove it.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
---
 fs/dlm/lock.c |    9 +++------
 1 files changed, 3 insertions(+), 6 deletions(-)

  compile tested only.

diff --git a/fs/dlm/lock.c b/fs/dlm/lock.c
index f71d0b5..a18ecff 100644
--- a/fs/dlm/lock.c
+++ b/fs/dlm/lock.c
@@ -849,9 +849,8 @@ void dlm_scan_waiters(struct dlm_ls *ls)
 
 		if (!num_nodes) {
 			num_nodes = ls->ls_num_nodes;
-			warned = kmalloc(GFP_KERNEL, num_nodes * sizeof(int));
-			if (warned)
-				memset(warned, 0, num_nodes * sizeof(int));
+			kfree(warned);
+			warned = kzalloc(GFP_KERNEL, num_nodes * sizeof(int));
 		}
 		if (!warned)
 			continue;
@@ -863,9 +862,7 @@ void dlm_scan_waiters(struct dlm_ls *ls)
 			  dlm_config.ci_waitwarn_us, lkb->lkb_wait_nodeid);
 	}
 	mutex_unlock(&ls->ls_waiters_mutex);
-
-	if (warned)
-		kfree(warned);
+	kfree(warned);
 
 	if (debug_expired)
 		log_debug(ls, "scan_waiters %u warn %u over %d us max %lld us",
-- 
1.7.6

-- 
Jesper Juhl <jj@chaosbits.net>       http://www.chaosbits.net/
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Re: [PATCH] fs, dlm: Don't leak, don't do pointless NULL checks and use kzalloc

[David Teigland]

On Wed, Jun 29, 2011 at 11:09:27PM +0200, Jesper Juhl wrote:
> In fs/dlm/lock.c in the dlm_scan_waiters() function there are 3 small
> issues:
> 
> 1) first time through the loop we allocate memory for 'warned', if we
> then (in the loop) don't take the "if (!warned)" path and loop again,
> the second time through the loop we'll allocate memory again and store
> it to 'warned' without freeing the previous allocation - this leaks
> memory.

I don't think so; num_nodes won't be set to zero.

> 2) There's no need to test the return value of the allocation and do a
> memset if is succeedes. Just use kzalloc() to obtain zeroed memory.

fine

> 3) Since kfree() handles NULL pointers gracefully, the test of
> 'warned' against NULL before the kfree() after the loop is completely
> pointless. Remove it.

fine

ack if you want to push those two out yourself.
Dave

Re: [PATCH] fs, dlm: Don't leak, don't do pointless NULL checks and use kzalloc

[Jesper Juhl]

On Wed, 29 Jun 2011, David Teigland wrote:

> On Wed, Jun 29, 2011 at 11:09:27PM +0200, Jesper Juhl wrote:
> > In fs/dlm/lock.c in the dlm_scan_waiters() function there are 3 small
> > issues:
> > 
> > 1) first time through the loop we allocate memory for 'warned', if we
> > then (in the loop) don't take the "if (!warned)" path and loop again,
> > the second time through the loop we'll allocate memory again and store
> > it to 'warned' without freeing the previous allocation - this leaks
> > memory.
> 
> I don't think so; num_nodes won't be set to zero.
> 

Hmm. How so?  Maybe I'm missing something obvious, but;
num_nodes is initialized to zero at the beginning of the function, which 
means that we'll definately do the first allocation in the loop.
We then set num_nodes equal to ls->ls_num_nodes - what guarantees that 
this will not be zero so we won't do a second allocation (and leak) the 
second time through the loop?

> > 2) There's no need to test the return value of the allocation and do a
> > memset if is succeedes. Just use kzalloc() to obtain zeroed memory.
> 
> fine
> 
> > 3) Since kfree() handles NULL pointers gracefully, the test of
> > 'warned' against NULL before the kfree() after the loop is completely
> > pointless. Remove it.
> 
> fine
> 
> ack if you want to push those two out yourself.
> Dave

Ok. I can resend a patch (tomorrow) with just those two changes and will 
add your Acked-by:

-- 
Jesper Juhl <jj@chaosbits.net>       http://www.chaosbits.net/
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Re: [PATCH] fs, dlm: Don't leak, don't do pointless NULL checks and use kzalloc

[David Teigland]

On Wed, Jun 29, 2011 at 11:51:00PM +0200, Jesper Juhl wrote:
> > I don't think so; num_nodes won't be set to zero.
> 
> Hmm. How so?  Maybe I'm missing something obvious, but;
> num_nodes is initialized to zero at the beginning of the function, which 
> means that we'll definately do the first allocation in the loop.

Zero is meant to mean "first time through the loop".

> We then set num_nodes equal to ls->ls_num_nodes - what guarantees that 
> this will not be zero so we won't do a second allocation (and leak) the 
> second time through the loop?

That's just the nature of a lockspace, I guess -- it doesn't make sense or
exist without nodes in it.  I doubt any of the dlm code would work if that
weren't true.

Dave

Re: [PATCH] fs, dlm: Don't leak, don't do pointless NULL checks and use kzalloc

[Jesper Juhl]

On Wed, 29 Jun 2011, David Teigland wrote:

> On Wed, Jun 29, 2011 at 11:51:00PM +0200, Jesper Juhl wrote:
> > > I don't think so; num_nodes won't be set to zero.
> > 
> > Hmm. How so?  Maybe I'm missing something obvious, but;
> > num_nodes is initialized to zero at the beginning of the function, which 
> > means that we'll definately do the first allocation in the loop.
> 
> Zero is meant to mean "first time through the loop".
> 
> > We then set num_nodes equal to ls->ls_num_nodes - what guarantees that 
> > this will not be zero so we won't do a second allocation (and leak) the 
> > second time through the loop?
> 
> That's just the nature of a lockspace, I guess -- it doesn't make sense or
> exist without nodes in it.  I doubt any of the dlm code would work if that
> weren't true.
> 
Thank you for the explanation.

I've prepared a new patch with just the changes you ack'ed. I'll send it 
in a minute.

-- 
Jesper Juhl <jj@chaosbits.net>       http://www.chaosbits.net/
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