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

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Date:   Sun, 5 Feb 2017 20:56:17 +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 list <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 Sun, Feb 05, 2017 at 01:51:49AM +0000, Al Viro wrote:

> IDGI.  Your request is marked aborted and should presumably fail, so
> that when request_wait_answer() wakes up and finds it screwed, fuse_readpage()
> would just return an error and filemap_fault() will return VM_FAULT_SIGBUS,
> with page left not uptodate and _not_ inserted into page tables.  What's
> leaking where?

Egads...  Do you mean that req->pages[] contents can be dropped by connection
abort right under fuse_copy_pages()?  Or is it that args[...].value can
end up freed under you?

<goes to look at the ->end() callbacks>

Both, apparently, plus the request initiator might have seen that
request has failed and buggered off, with args[...].value pointing to
what used to be initiator's stack frame.  Is that what you are talking about?

If so, why not mark request as "being handled by fuse_dev_do_{read,write}()"
for the duration, and leave the request_end() on such requests for
fuse_dev_do_{read,write}(), seeing that they will call request_end() for such
anyway?

Looks like your FR_LOCKED is not far from that already.  Why not stop
dropping/regaining FR_LOCKED in lock_request()/unlock_request() and simply
have your
                end_requests(fc, &to_end2);
in fuse_abort_conn() skip the actual calls of request_end()?