Re: kern/45634: hardclock_ticks corner cases in vflushnext() et al

[Christian Biere <christianbiere%gmx.de@localhost>]

The following reply was made to PR kern/45634; it has been noted by GNATS.

From: Christian Biere <christianbiere%gmx.de@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: kern/45634: hardclock_ticks corner cases in vflushnext() et al
Date: Wed, 23 Nov 2011 20:53:02 +0100

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 The attached patch should avoid the mentioned integer overflows in vflushnext()
 by using the proper arithmetic methods and ensure that the conditional code is 
actually invoked when the declared amount of ticks has passed.
 
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 --- vfs_mount.c.orig   2011-11-23 19:28:41.334186185 +0100
 +++ vfs_mount.c        2011-11-23 20:36:55.004184864 +0100
 @@ -420,14 +420,15 @@
  #endif
  
  static vnode_t *
 -vflushnext(vnode_t *mvp, int *when)
 +vflushnext(vnode_t *mvp, unsigned *when, unsigned dly)
  {
 +      unsigned dt = hardclock_ticks + dly - *when;
  
 -      if (hardclock_ticks > *when) {
 +      if (dt > dly) {
                mutex_exit(&mntvnode_lock);
                yield();
                mutex_enter(&mntvnode_lock);
 -              *when = hardclock_ticks + hz / 10;
 +              *when = hardclock_ticks + dly;
        }
        return vunmark(mvp);
  }
 @@ -436,7 +437,7 @@
  vflush(struct mount *mp, vnode_t *skipvp, int flags)
  {
        vnode_t *vp, *mvp;
 -      int busy = 0, when = 0;
 +      unsigned busy = 0, dly = 10 / hz, when = hardclock_ticks - dly - 1;
  
        /* First, flush out any vnode references from vrele_list. */
        vrele_flush();
 @@ -450,7 +451,7 @@
         */
        mutex_enter(&mntvnode_lock);
        for (vp = TAILQ_FIRST(&mp->mnt_vnodelist); vp != NULL;
 -          vp = vflushnext(mvp, &when)) {
 +          vp = vflushnext(mvp, &when, dly)) {
                vmark(mvp, vp);
                if (vp->v_mount != mp || vismarker(vp))
                        continue;
 
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