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