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autofs-5.0.6 - fix recursive mount deadlock
From: Ian Kent <raven@themaw.net>
Prior to the vfs-automount changes that went into 2.6.38
and were finalized in 3.1 it was not possible to block
path walks into multi-mounts whose root was covered by
another mount. To deal with that a write lock was used
to ensure the mount tree construction was completed. This
restricts the types of recursively defined mount maps that
can be used and can lead to a deadlock during lookup.
Now that we can prevent processes walking into multi-mounts
that are under construction we no longer need to use a
write lock.
Also, in the patch below, a cache writelock is changed to
a read lock because a write lock isn't needed since the
map cache entry isn't being updated.
---
CHANGELOG | 1 +
daemon/direct.c | 14 ++++++++++++--
2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/CHANGELOG b/CHANGELOG
index 936c9ab..9cdad6e 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -12,6 +12,7 @@
- configure.in: allow cross compilation.
- README: update mailing list subscription info.
- allow non root user to check status.
+- fix recursive mount deadlock.
25/07/2012 autofs-5.0.7
=======================
diff --git a/daemon/direct.c b/daemon/direct.c
index 7e2f0d7..3e09c5d 100644
--- a/daemon/direct.c
+++ b/daemon/direct.c
@@ -1285,6 +1285,8 @@ int handle_packet_missing_direct(struct autofs_point *ap, autofs_packet_missing_
struct timespec wait;
struct timeval now;
int ioctlfd, len, state;
+ unsigned int kver_major = get_kver_major();
+ unsigned int kver_minor = get_kver_minor();
pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &state);
@@ -1297,8 +1299,16 @@ int handle_packet_missing_direct(struct autofs_point *ap, autofs_packet_missing_
* cache entry we will not be able to find the mapent. So
* we must take the source writelock to ensure the parent
* has mount is complete before we look for the entry.
+ *
+ * Since the vfs-automount kernel changes we can now block
+ * on covered mounts during mount tree construction so a
+ * write lock is no longer needed. So we now can handle a
+ * wider class of recursively define mount lookups.
*/
- master_source_writelock(ap->entry);
+ if (kver_major > 5 || (kver_major == 5 && kver_minor > 1))
+ master_source_readlock(ap->entry);
+ else
+ master_source_writelock(ap->entry);
map = ap->entry->maps;
while (map) {
/*
@@ -1311,7 +1321,7 @@ int handle_packet_missing_direct(struct autofs_point *ap, autofs_packet_missing_
}
mc = map->mc;
- cache_writelock(mc);
+ cache_readlock(mc);
me = cache_lookup_ino(mc, pkt->dev, pkt->ino);
if (me)
break;
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