[RFC] Don't propagate automount

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An access to automounted filesystem can deadlock if it is a bind
mount on shared mounts. A user program should not deadlock the kernel
while automount waits for propagation of the mount. This is explained
at https://bugzilla.redhat.com/show_bug.cgi?id=1358887#c10
I am not sure completely blocking automount is the best solution,
so please reply with what is the best course of action to do
in such a situation.

Propagation of dentry with DCACHE_NEED_AUTOMOUNT can lead to
propagation of mount points without automount maps and not under
automount control. So, do not propagate them.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>

diff --git a/fs/pnode.c b/fs/pnode.c
index 49f6d7ff2139..b960805d7954 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -292,6 +292,9 @@ int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
 	struct mount *m, *n;
 	int ret = 0;
 
+	if (source_mnt->mnt_mountpoint->d_flags & DCACHE_NEED_AUTOMOUNT)
+		return 0;
+
 	/*
 	 * we don't want to bother passing tons of arguments to
 	 * propagate_one(); everything is serialized by namespace_sem,

-- 
Goldwyn



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