linux-kernel - Re: [PATCH v3 0/2] iov_iter: allow iov_iter_get_pages

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Message-ID: <20170204030842.GL27291@ZenIV.linux.org.uk>
Date:   Sat, 4 Feb 2017 03:08:42 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nfs@...r.kernel.org, ceph-devel@...r.kernel.org,
        lustre-devel@...ts.lustre.org,
        v9fs-developer@...ts.sourceforge.net,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Jeff Layton <jlayton@...hat.com>
Subject: Re: [PATCH v3 0/2] iov_iter: allow iov_iter_get_pages_alloc to
 allocate more pages per call

On Thu, Feb 02, 2017 at 09:51:25AM +0000, Al Viro wrote:

> 	* fuse_copy_fill().  I'm not at all sure that iov_iter_get_pages()
> is a good idea there - fuse_copy_do() could bloody well just use
> copy_{to,from}_iter().

Miklos, could you explain why does lock_request() prohibit page faults until
the matching unlock_request()?  All it does is setting FR_LOCKED on
our request and the only thing that even looks at that is fuse_abort_conn(),
which doesn't (AFAICS) wait for anything.

Where does the deadlock come from, and if it's not a deadlock - what is
it?  Or is that comment stale since "fuse: simplify request abort"?