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XFS: remove pointless conditional testing 'nmp' vs NULL in fs/xfs/xfs_rtalloc.c::xfs_growfs_rt()

PATCH In review Jesper Juhl 2 participants 5 messages Aug 12, 2006 – Aug 17, 2006 XFS filesystem

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Jesper Juhl

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#0 lore raw

PATCH 1/1 XFS: remove pointless conditional testing 'nmp' vs NULL in fs/xfs/xfs_rtalloc.c::xfs_growfs_rt()

In fs/xfs/xfs_rtalloc.c::xfs_growfs_rt() there's a completely useless conditional at the error_exit label.
The 'if (nmp)' check is pointless and might as well be removed for two reasons.
1) if 'nmp' is NULL then kmem_free() will end up calling kfree() with a NULL argument - which in turn will just cause a return from kfree(). No harm done.
2) At the beginning of the function there's an assignment; '*nmp = *mp;' so if 'nmp' was NULL we'd already have blown up due to dereferencing a NULL pointer.

This patch gets rid of the pointless check.

Signed-off-by Jesper Juhl <[email protected]>

---

 fs/xfs/xfs_rtalloc.c |    3 +--
 1 files changed, 1 insertion(+), 2 deletions(-)
fs/xfs/xfs_rtalloc.c +1 -2
@@ -2107,8 +2107,7 @@ xfs_growfs_rt(
 	 * Error paths come here.
 	 */
 error_exit:
-	if (nmp)
-		kmem_free(nmp, sizeof(*nmp));
+	kmem_free(nmp, sizeof(*nmp));
 	xfs_trans_cancel(tp, cancelflags);
 	return error;
 }
#1 lore raw
Quoted 8 lines · Jesper Juhl

In fs/xfs/xfs_rtalloc.c::xfs_growfs_rt() there's a completely useless conditional at the error_exit label.
The 'if (nmp)' check is pointless and might as well be removed for two reasons.

1) if 'nmp' is NULL then kmem_free() will end up calling kfree() with a NULL argument - which in turn will just cause a return from kfree(). No harm done.

Thats valid.

Quoted 1 line

2) At the beginning of the function there's an assignment; '*nmp = *mp;' so

Thats not. Theres no assignment at the start of the function; theres one inside the main body of the loop 20+ lines into it, and right after a mem alloc with flags requiring no failure. Later that local variable is freed then set to NULL inside the loop, before continuing the next iteration...

Really this code would be better if reworked slightly to just allocate nmp once before entering the loop, and then free it once at the end... we wouldn't need a goto, just a few breaks in the loop and a conditional transaction cancel.

Quoted 1 line

This patch gets rid of the pointless check.

Hmm, seems like code churn that makes the code slightly less obvious, but thats just me... I'd prefer a tested patch that implements the above suggestion, to be honest. :)

cheers.

Signature · 1 line
Nathan
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#2 lore raw
Quoted 25 lines · Nathan Scott
Quoted 8 lines · Jesper Juhl

In fs/xfs/xfs_rtalloc.c::xfs_growfs_rt() there's a completely useless conditional at the error_exit label.
The 'if (nmp)' check is pointless and might as well be removed for two reasons.

1) if 'nmp' is NULL then kmem_free() will end up calling kfree() with a NULL argument - which in turn will just cause a return from kfree(). No harm done.

Thats valid.

Quoted 1 line

2) At the beginning of the function there's an assignment; '*nmp = *mp;' so

Thats not. Theres no assignment at the start of the function; theres one inside the main body of the loop 20+ lines into it, and right after a mem alloc with flags requiring no failure. Later that local variable is freed then set to NULL inside the loop, before continuing the next iteration...

Really this code would be better if reworked slightly to just allocate nmp once before entering the loop, and then free it once at the end... we wouldn't need a goto, just a few breaks in the loop and a conditional transaction cancel.

Quoted 6 lines
Quoted 1 line

This patch gets rid of the pointless check.

Hmm, seems like code churn that makes the code slightly less obvious, but thats just me... I'd prefer a tested patch that implements the above suggestion, to be honest. :)

Ok, I'll see what I can come up with.

Signature · 3 lines
Jesper Juhl <[email protected]>
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#3 lore raw
Quoted 8 lines · Jesper Juhl
Quoted 7 lines · Nathan Scott

On Sun, Aug 13, 2006 at 12:16:50AM +0200, Jesper Juhl wrote:

Really this code would be better if reworked slightly to just allocate nmp once before entering the loop, and then free it once at the end... we wouldn't need a goto, just a few breaks in the loop and a conditional transaction cancel.

Quoted 8 lines
Quoted 6 lines
Quoted 1 line

This patch gets rid of the pointless check.

Hmm, seems like code churn that makes the code slightly less obvious, but thats just me... I'd prefer a tested patch that implements the above suggestion, to be honest. :)

Ok, I'll see what I can come up with.

How this?

Compile tested only since I'm at home and don't have any XFS filesystems to play with atm.

Rework fs/xfs/xfs_rtalloc.c::xfs_growfs_rt() to allocate and free 'nmp' just once and make the error handling a bit clearer.

Signed-off-by Jesper Juhl <[email protected]>

---

 fs/xfs/xfs_rtalloc.c |   37 +++++++++++++++----------------------
 1 files changed, 15 insertions(+), 22 deletions(-)
fs/xfs/xfs_rtalloc.c +15 -22
@@ -1976,7 +1976,11 @@ xfs_growfs_rt(
 	if ((error = xfs_growfs_rt_alloc(mp, rsumblocks, nrsumblocks,
 			mp->m_sb.sb_rsumino)))
 		return error;
-	nmp = NULL;
+
+	/*
+	 * Allocate a new (fake) mount/sb.
+	 */
+	nmp = kmem_alloc(sizeof(*nmp), KM_SLEEP);
 	/*
 	 * Loop over the bitmap blocks.
 	 * We will do everything one bitmap block at a time.

@@ -1987,10 +1991,6 @@ xfs_growfs_rt(
 		     ((sbp->sb_rextents & ((1 << mp->m_blkbit_log) - 1)) != 0);
 	     bmbno < nrbmblocks;
 	     bmbno++) {
-		/*
-		 * Allocate a new (fake) mount/sb.
-		 */
-		nmp = kmem_alloc(sizeof(*nmp), KM_SLEEP);
 		*nmp = *mp;
 		nsbp = &nmp->m_sb;
 		/*

@@ -2018,13 +2018,13 @@ xfs_growfs_rt(
 		cancelflags = 0;
 		if ((error = xfs_trans_reserve(tp, 0,
 				XFS_GROWRTFREE_LOG_RES(nmp), 0, 0, 0)))
-			goto error_exit;
+			break;
 		/*
 		 * Lock out other callers by grabbing the bitmap inode lock.
 		 */
 		if ((error = xfs_trans_iget(mp, tp, mp->m_sb.sb_rbmino, 0,
 						XFS_ILOCK_EXCL, &ip)))
-			goto error_exit;
+			break;
 		ASSERT(ip == mp->m_rbmip);
 		/*
 		 * Update the bitmap inode's size.

@@ -2038,7 +2038,7 @@ xfs_growfs_rt(
 		 */
 		if ((error = xfs_trans_iget(mp, tp, mp->m_sb.sb_rsumino, 0,
 						XFS_ILOCK_EXCL, &ip)))
-			goto error_exit;
+			break;
 		ASSERT(ip == mp->m_rsumip);
 		/*
 		 * Update the summary inode's size.

@@ -2053,7 +2053,7 @@ xfs_growfs_rt(
 		    mp->m_rsumlevels != nmp->m_rsumlevels) {
 			error = xfs_rtcopy_summary(mp, nmp, tp);
 			if (error)
-				goto error_exit;
+				break;
 		}
 		/*
 		 * Update superblock fields.

@@ -2080,18 +2080,13 @@ xfs_growfs_rt(
 		error = xfs_rtfree_range(nmp, tp, sbp->sb_rextents,
 			nsbp->sb_rextents - sbp->sb_rextents, &bp, &sumbno);
 		if (error)
-			goto error_exit;
+			break;
 		/*
 		 * Mark more blocks free in the superblock.
 		 */
 		xfs_trans_mod_sb(tp, XFS_TRANS_SB_FREXTENTS,
 			nsbp->sb_rextents - sbp->sb_rextents);
 		/*
-		 * Free the fake mp structure.
-		 */
-		kmem_free(nmp, sizeof(*nmp));
-		nmp = NULL;
-		/*
 		 * Update mp values into the real mp structure.
 		 */
 		mp->m_rsumlevels = nrsumlevels;

@@ -2101,15 +2096,13 @@ xfs_growfs_rt(
 		 */
 		xfs_trans_commit(tp, 0, NULL);
 	}
-	return 0;
-
+	if (error)
+		xfs_trans_cancel(tp, cancelflags);
 	/*
-	 * Error paths come here.
+	 * Free the fake mp structure.
 	 */
-error_exit:
-	if (nmp)
-		kmem_free(nmp, sizeof(*nmp));
-	xfs_trans_cancel(tp, cancelflags);
+	kmem_free(nmp, sizeof(*nmp));
+
 	return error;
 }
#4 lore raw
Quoted 10 lines · Jesper Juhl
Quoted 9 lines · Jesper Juhl
Quoted 8 lines · Nathan Scott
Quoted 1 line · Jesper Juhl

This patch gets rid of the pointless check.

Hmm, seems like code churn that makes the code slightly less obvious, but thats just me... I'd prefer a tested patch that implements the above suggestion, to be honest. :)

Quoted 7 lines
Quoted 2 lines

Ok, I'll see what I can come up with.

How this?

Compile tested only since I'm at home and don't have any XFS filesystems to play with atm.

It looks good. I've tested it, and it works fine - I'll merge it into my tree shortly. Thanks for following up on this.

cheers.

Signature · 1 line
Nathan