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Reduce stack usage in time.c

PATCH In review Yum Rayan 4 participants 4 messages Mar 31, 2005

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Yum Rayan

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#0 lore raw

PATCH 1/1 Reduce stack usage in time.c

Attempt to reduce stack usage in time.c (linux-2.6.12-rc1-mm3). Stack usage was noted using checkstack.pl. Specifically:

Before patch
------------
sys_adjtimex - 128

After patch
-----------
sys_adjtimex - none (register usage only)

Signed-off-by Yum Rayan <[email protected]>
kernel/time.c +16 -6
@@ -413,17 +413,27 @@
 
 asmlinkage long sys_adjtimex(struct timex __user *txc_p)
 {
-	struct timex txc;		/* Local copy of parameter */
-	int ret;
+	struct timex *txc;		/* Local copy of parameter */
+	int retval;
+
+	txc = kmalloc(sizeof(struct timex), GFP_KERNEL);
+	if (!txc)
+		return -ENOMEM;
 
 	/* Copy the user data space into the kernel copy
 	 * structure. But bear in mind that the structures
 	 * may change
 	 */
-	if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
-		return -EFAULT;
-	ret = do_adjtimex(&txc);
-	return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
+	if(copy_from_user(txc, txc_p, sizeof(struct timex))) {
+		retval = -EFAULT;
+		goto free_txc;
+	}
+	retval = do_adjtimex(txc);
+	if (copy_to_user(txc_p, txc, sizeof(struct timex)))
+		retval = -EFAULT;
+free_txc:
+	kfree(txc);
+	return retval;
 }
 
 inline struct timespec current_kernel_time(void)
#1 lore raw
Quoted 34 lines · Yum Rayan

Attempt to reduce stack usage in time.c (linux-2.6.12-rc1-mm3). Stack usage was noted using checkstack.pl. Specifically:

Before patch
------------
sys_adjtimex - 128

After patch
-----------
sys_adjtimex - none (register usage only)

Signed-off-by Yum Rayan <[email protected]>
kernel/time.c +6 -4
@@ -413,17 +413,27 @@
 
 asmlinkage long sys_adjtimex(struct timex __user *txc_p)
 {
-	struct timex txc;		/* Local copy of parameter */
-	int ret;
+	struct timex *txc;		/* Local copy of parameter */
+	int retval;
+
+	txc = kmalloc(sizeof(struct timex), GFP_KERNEL);
+	if (!txc)
+		return -ENOMEM;
 
 	/* Copy the user data space into the kernel copy
 	 * structure. But bear in mind that the structures
 	 * may change
 	 */
-	if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
-		return -EFAULT;

kernel/time.c line 434

Quoted 10 lines
kernel/time.c +8 -2
-	ret = do_adjtimex(&txc);
-	return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
+	if(copy_from_user(txc, txc_p, sizeof(struct timex))) {
+		retval = -EFAULT;
+		goto free_txc;
+	}
+	retval = do_adjtimex(txc);
+	if (copy_to_user(txc_p, txc, sizeof(struct timex)))
+		retval = -EFAULT;
+free_txc:

It seems quite unhealthy to add a kmalloc(,GFP_KERNEL) allocation into a time-sensitive function.

Jeff

#2 lore raw
Quoted 29 lines · Jeff Garzik
Quoted 28 lines · Yum Rayan

Attempt to reduce stack usage in time.c (linux-2.6.12-rc1-mm3). Stack usage was noted using checkstack.pl. Specifically:

Before patch
------------
sys_adjtimex - 128

After patch
-----------
sys_adjtimex - none (register usage only)

Signed-off-by Yum Rayan <[email protected]>
kernel/time.c +6 -2
@@ -413,17 +413,27 @@
 
 asmlinkage long sys_adjtimex(struct timex __user *txc_p)
 {
-	struct timex txc;		/* Local copy of parameter */
-	int ret;
+	struct timex *txc;		/* Local copy of parameter */
+	int retval;
+
+	txc = kmalloc(sizeof(struct timex), GFP_KERNEL);
+	if (!txc)
+		return -ENOMEM;
Quoted 16 lines
Quoted 6 lines
kernel/time.c +0 -2
 	/* Copy the user data space into the kernel copy
 	 * structure. But bear in mind that the structures
 	 * may change
 	 */
-	if(copy_from_user(&txc, txc_p, sizeof(struct timex)))
-		return -EFAULT;

kernel/time.c line 434

Quoted 10 lines
kernel/time.c +8 -2
-	ret = do_adjtimex(&txc);
-	return copy_to_user(txc_p, &txc, sizeof(struct timex)) ? -EFAULT : ret;
+	if(copy_from_user(txc, txc_p, sizeof(struct timex))) {
+		retval = -EFAULT;
+		goto free_txc;
+	}
+	retval = do_adjtimex(txc);
+	if (copy_to_user(txc_p, txc, sizeof(struct timex)))
+		retval = -EFAULT;
+free_txc:

Is this a syscall?
Is it ever called from some deeply nested kernel function? --
vda

#3 lore raw
Quoted 3 lines · Denis Vlasenko

Is this a syscall?
Is it ever called from some deeply nested kernel function?

Never showed up in any of my callchain-tests. I'd leave it as is.

Jörn

Signature · 4 lines
When I am working on a problem I never think about beauty.  I think
only how to solve the problem.  But when I have finished, if the
solution is not beautiful, I know it is wrong.
-- R. Buckminster Fuller