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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Kiran Kumar Modukuri <kiran.modukuri@gmail.com>,
        David Howells <dhowells@redhat.com>,
        Sasha Levin <alexander.levin@microsoft.com>
Subject: [PATCH 4.4 29/80] cachefiles: Wait rather than BUGing on "Unexpected object collision"
Date:   Mon,  3 Sep 2018 18:49:07 +0200
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4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kiran Kumar Modukuri <kiran.modukuri@gmail.com>

[ Upstream commit c2412ac45a8f8f1cd582723c1a139608694d410d ]

If we meet a conflicting object that is marked FSCACHE_OBJECT_IS_LIVE in
the active object tree, we have been emitting a BUG after logging
information about it and the new object.

Instead, we should wait for the CACHEFILES_OBJECT_ACTIVE flag to be cleared
on the old object (or return an error).  The ACTIVE flag should be cleared
after it has been removed from the active object tree.  A timeout of 60s is
used in the wait, so we shouldn't be able to get stuck there.

Fixes: 9ae326a69004 ("CacheFiles: A cache that backs onto a mounted filesystem")
Signed-off-by: Kiran Kumar Modukuri <kiran.modukuri@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/cachefiles/namei.c |    1 -
 1 file changed, 1 deletion(-)

--- a/fs/cachefiles/namei.c
+++ b/fs/cachefiles/namei.c
@@ -194,7 +194,6 @@ wait_for_old_object:
 		pr_err("\n");
 		pr_err("Error: Unexpected object collision\n");
 		cachefiles_printk_object(object, xobject);
-		BUG();
 	}
 	atomic_inc(&xobject->usage);
 	write_unlock(&cache->active_lock);