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Re: xfs_file_splice_read: possible circular locking dependency detected

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: xfs_file_splice_read: possible circular locking dependency detected
From: CAI Qian <caiqian@xxxxxxxxxx>
Date: Tue, 6 Sep 2016 17:53:59 -0400 (EDT)
Cc: linux-xfs <linux-xfs@xxxxxxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Al Viro <viro@xxxxxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20160903003919.GI30056@dastard>
References: <723420070.1340881.1472835555274.JavaMail.zimbra@xxxxxxxxxx> <1832555471.1341372.1472835736236.JavaMail.zimbra@xxxxxxxxxx> <20160903003919.GI30056@dastard>
Thread-index: SGvn4G5xBSzKbnLtClJQOQtHfOp9ZA==
Thread-topic: xfs_file_splice_read: possible circular locking dependency detected

----- Original Message -----
> Fundamentally a splice infrastructure problem. If we let splice race
> with hole punch and other fallocate() based extent manipulations to
> avoid this lockdep warning, we allow potential for read or write to
> regions of the file that have been freed. We can live with having
> lockdep complain about this potential deadlock as it is unlikely to
> ever occur in practice. The other option is simply not an acceptible
> solution....
The problem with living with having this lockdep complain that
it seems once this lockdep happens, it will prevent other complains from
showing up. For example, I have to apply the commit dc3a04d to fix an early
rcu lockdep first during the bisecting.
   CAI Qian

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