kern/163318: commit references a PR

[dfilter service]

The following reply was made to PR kern/163318; it has been noted by GNATS.

From: dfilter at FreeBSD.ORG (dfilter service)
To: bug-followup at FreeBSD.org
Cc:  
Subject: Re: kern/163318: commit references a PR
Date: Fri,  2 Mar 2012 02:53:55 +0000 (UTC)

 Author: adrian
 Date: Fri Mar  2 02:53:43 2012
 New Revision: 232373
 URL: http://svn.freebsd.org/changeset/base/232373
 
 Log:
   Attempt to catch scan cancellations at exactly the wrong time from occuring.
   
   The scan code unlocks the comlock and calls into the driver.  It then
   assumes the state hasn't changed from underneath it.
   
   Although I haven't seen this particular condition trigger, I'd like to
   be informed if I or anyone else sees it.
   
   What I'm thinking may occur:
   
   * A cancellation comes in during the scan_end call;
   * the cancel flag is set;
   * but it's never checked, so scandone isn't updated;
   * .. and the interface stays in the STA power save mode.
   
   It's a subtle race, if it even exists.
   
   PR:		kern/163318
 
 Modified:
   head/sys/net80211/ieee80211_scan.c
 
 Modified: head/sys/net80211/ieee80211_scan.c
 ==============================================================================
 --- head/sys/net80211/ieee80211_scan.c	Fri Mar  2 00:21:07 2012	(r232372)
 +++ head/sys/net80211/ieee80211_scan.c	Fri Mar  2 02:53:43 2012	(r232373)
 @@ -960,6 +960,19 @@ scan_task(void *arg, int pending)
  	IEEE80211_LOCK(ic);
  
  	/*
 +	 * Since a cancellation may have occured during one of the
 +	 * driver calls (whilst unlocked), update scandone.
 +	 */
 +	if (scandone == 0 &&
 +	    ((SCAN_PRIVATE(ss)->ss_iflags & ISCAN_CANCEL) != 0)) {
 +		/* XXX printf? */
 +		if_printf(vap->iv_ifp,
 +		    "%s: OOPS! scan cancelled during driver call!\n",
 +		    __func__);
 +	}
 +	scandone |= ((SCAN_PRIVATE(ss)->ss_iflags & ISCAN_CANCEL) != 0);
 +
 +	/*
  	 * Record scan complete time.  Note that we also do
  	 * this when canceled so any background scan will
  	 * not be restarted for a while.
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