Merged revisions 1468 via svnmerge from

https://origsvn.digium.com/svn/zaptel/branches/1.2

........
r1468 | tilghman | 2006-09-16 02:45:04 -0500 (Sat, 16 Sep 2006) | 4 lines

Round two of the fix for "hard-safe -> hard-unsafe lock order detected" (Issue 7620)
Only difference is that the fix is only defined for kernel versions 2.6.11 and
above; older kernels keep the current (possible deadlocking) code.

........


git-svn-id: http://svn.digium.com/svn/zaptel/trunk@1469 5390a7c7-147a-4af0-8ec9-7488f05a26cb

1 files changed, 15 insertions, 2 deletions

diff --git a/zaptel.c b/zaptel.c
index bf561ff..df920de 100644
--- a/zaptel.c
+++ b/zaptel.c
@@ -1154,8 +1154,21 @@ static int set_tone_zone(struct zt_chan *chan, int zone)
 	/* Assumes channel is already locked */
 	if ((zone >= ZT_TONE_ZONE_MAX) || (zone < -1))
 		return -EINVAL;
-	
+
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,11)
+	/* Since this routine is called both from IRQ as well as from userspace,
+	 * it is possible that we could be called during an IRQ while userspace
+	 * has locked this.  However unlikely, this could possibly cause a
+	 * deadlock. */
+	if (! read_trylock(&zone_lock))
+		return -EWOULDBLOCK;
+#else
+	/* But there are no trylock macros for kernel versions before 2.6.11,
+	 * so we do the unsafe thing anyway.  Such is the problem for dealing
+	 * with old, buggy kernels. */
 	read_lock(&zone_lock);
+#endif
+
 	if (zone == -1) {
 		zone = default_zone;
 	}
@@ -1166,7 +1179,7 @@ static int set_tone_zone(struct zt_chan *chan, int zone)
 	} else {
 		res = -ENODATA;
 	}
-	
+
 	read_unlock(&zone_lock);
 	return res;
 }