Re: [PATCH] Reduce stack usage in time.c
From: Jeff Garzik (jgarzik_at_pobox.com)
Date: 03/31/05
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Date: Thu, 31 Mar 2005 03:26:43 -0500 To: Yum Rayan <yum.rayan@gmail.com>
Yum Rayan wrote:
> 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 <yum.rayan@gmail.com>
>
> --- a/kernel/time.c 2005-03-25 22:11:06.000000000 -0800
> +++ b/kernel/time.c 2005-03-30 16:59:51.000000000 -0800
> @@ -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:
It seems quite unhealthy to add a kmalloc(,GFP_KERNEL) allocation into a
time-sensitive function.
Jeff
-
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