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Date:   Sat, 20 Feb 2021 19:40:49 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     syzbot <syzbot+3d2c27c2b7dc2a94814d@syzkaller.appspotmail.com>,
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Subject: Re: WARNING in iov_iter_revert (2)
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On Sat, Feb 20, 2021 at 07:29:57PM +0000, Al Viro wrote:

> And then you notice that it has reports
> successful write of amount other than what you'd passed and tries
> to pull back.

Sorry, half-edited sentence has escaped ;-/  Should be

"And there the caller notices that callback has reported a successful
write, but the amount apparently written is not the same as the
amount it had asked to write.  It interprets that as a short write
and tries to pull back.  Only it's actually _forward_, since we'd
asked to write 0 bytes and got a small positive number from the
callback."