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Date:   Mon, 4 Jul 2022 21:07:43 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Alexander Potapenko <glider@google.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexei Starovoitov <ast@kernel.org>,
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Subject: Re: [PATCH v4 44/45] mm: fs: initialize fsdata passed to
 write_begin/write_end interface
Message-ID: <YsNIjwTw41y0Ij0n@casper.infradead.org>
References: <20220701142310.2188015-1-glider@google.com>
 <20220701142310.2188015-45-glider@google.com>
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On Fri, Jul 01, 2022 at 04:23:09PM +0200, Alexander Potapenko wrote:
> Functions implementing the a_ops->write_end() interface accept the
> `void *fsdata` parameter that is supposed to be initialized by the
> corresponding a_ops->write_begin() (which accepts `void **fsdata`).
> 
> However not all a_ops->write_begin() implementations initialize `fsdata`
> unconditionally, so it may get passed uninitialized to a_ops->write_end(),
> resulting in undefined behavior.

... wait, passing an uninitialised variable to a function *which doesn't
actually use it* is now UB?  What genius came up with that rule?  What
purpose does it serve?