From: Miklos Szeredi <miklos@szeredi.hu>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Linux NFS list <linux-nfs@vger.kernel.org>,
ceph-devel@vger.kernel.org, lustre-devel@lists.lustre.org,
v9fs-developer@lists.sourceforge.net,
Linus Torvalds <torvalds@linux-foundation.org>,
Jan Kara <jack@suse.cz>, Chris Wilson <chris@chris-wilson.co.uk>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Jeff Layton <jlayton@redhat.com>
Subject: Re: [PATCH v3 0/2] iov_iter: allow iov_iter_get_pages_alloc to allocate more pages per call
Date: Sat, 4 Feb 2017 23:11:27 +0100 [thread overview]
Message-ID: <CAJfpegtVb8PKNnKe5wGMd0u0WzgLpjpVtVpqDScbrBJShLAfGw@mail.gmail.com> (raw)
In-Reply-To: <20170204030842.GL27291@ZenIV.linux.org.uk>
On Sat, Feb 4, 2017 at 4:08 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> 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"?
Well, it's not historical; at least not yet. The deadlock is there
alright: mmap fuse file to addr; read byte from mapped page -> page
locked; this triggeres read request served in same process but
separate thread; write addr-headerlen to fuse dev; trying to lock same
page -> deadlock.
The deadlock can be broken by aborting or force unmounting: return
error for original read request; page unlocked; device write can get
page lock and return.
The reason we need to prohibit pagefault while copying is that when
request is aborted and the caller returns the memory in the request
may become invalid (e.g. data from stack).
Another solution would be to copy all data and keep a ref on the copy
by the request even after being aborted. This is the plan for the
future.
Thanks,
Miklos
WARNING: multiple messages have this Message-ID (diff)
From: Miklos Szeredi <miklos-sUDqSbJrdHQHWmgEVkV9KA@public.gmane.org>
To: Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
Cc: linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Linux NFS list
<linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
ceph-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
lustre-devel-aLEFhgZF4x6X6Mz3xDxJMA@public.gmane.org,
v9fs-developer-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
Linus Torvalds
<torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>,
Chris Wilson
<chris-Y6uKTt2uX1cEflXRtASbqLVCufUGDwFn@public.gmane.org>,
"Kirill A. Shutemov"
<kirill.shutemov-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>,
Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH v3 0/2] iov_iter: allow iov_iter_get_pages_alloc to allocate more pages per call
Date: Sat, 4 Feb 2017 23:11:27 +0100 [thread overview]
Message-ID: <CAJfpegtVb8PKNnKe5wGMd0u0WzgLpjpVtVpqDScbrBJShLAfGw@mail.gmail.com> (raw)
In-Reply-To: <20170204030842.GL27291-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
On Sat, Feb 4, 2017 at 4:08 AM, Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org> wrote:
> 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"?
Well, it's not historical; at least not yet. The deadlock is there
alright: mmap fuse file to addr; read byte from mapped page -> page
locked; this triggeres read request served in same process but
separate thread; write addr-headerlen to fuse dev; trying to lock same
page -> deadlock.
The deadlock can be broken by aborting or force unmounting: return
error for original read request; page unlocked; device write can get
page lock and return.
The reason we need to prohibit pagefault while copying is that when
request is aborted and the caller returns the memory in the request
may become invalid (e.g. data from stack).
Another solution would be to copy all data and keep a ref on the copy
by the request even after being aborted. This is the plan for the
future.
Thanks,
Miklos
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next prev parent reply other threads:[~2017-02-04 22:11 UTC|newest]
Thread overview: 101+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-24 21:23 [PATCH] iov_iter: allow iov_iter_get_pages_alloc to allocate more pages per call Jeff Layton
2017-01-25 13:32 ` [PATCH v3 0/2] " Jeff Layton
2017-01-25 13:32 ` [PATCH v3 1/2] " Jeff Layton
2017-01-26 12:35 ` Jeff Layton
2017-01-27 13:24 ` [PATCH v4 0/2] " Jeff Layton
2017-01-27 13:24 ` [PATCH v4 1/2] " Jeff Layton
2017-01-27 13:24 ` [PATCH v4 2/2] ceph: switch DIO code to use iov_iter_get_pages_alloc Jeff Layton
2017-01-30 15:40 ` Jeff Layton
2017-01-30 15:40 ` Jeff Layton
2017-01-25 13:32 ` [PATCH v3 " Jeff Layton
2017-02-02 9:51 ` [PATCH v3 0/2] iov_iter: allow iov_iter_get_pages_alloc to allocate more pages per call Al Viro
2017-02-02 9:51 ` [lustre-devel] " Al Viro
2017-02-02 9:51 ` Al Viro
2017-02-02 10:56 ` Christoph Hellwig
2017-02-02 10:56 ` [lustre-devel] " Christoph Hellwig
2017-02-02 10:56 ` Christoph Hellwig
2017-02-02 11:16 ` Al Viro
2017-02-02 11:16 ` [lustre-devel] " Al Viro
2017-02-02 11:16 ` Al Viro
2017-02-02 13:00 ` Jeff Layton
2017-02-02 13:00 ` Jeff Layton
2017-02-03 7:29 ` Al Viro
2017-02-03 7:29 ` [lustre-devel] " Al Viro
2017-02-03 7:29 ` Al Viro
2017-02-03 18:29 ` Linus Torvalds
2017-02-03 18:29 ` [lustre-devel] " Linus Torvalds
2017-02-03 18:29 ` Linus Torvalds
2017-02-03 19:08 ` Al Viro
2017-02-03 19:08 ` [lustre-devel] " Al Viro
2017-02-03 19:08 ` Al Viro
2017-02-03 19:28 ` Linus Torvalds
2017-02-03 19:28 ` [lustre-devel] " Linus Torvalds
2017-02-03 19:28 ` Linus Torvalds
2017-02-13 9:56 ` Steve Capper
2017-02-13 21:40 ` Linus Torvalds
2017-02-13 21:40 ` [lustre-devel] " Linus Torvalds
2017-02-13 21:40 ` Linus Torvalds
2017-02-03 7:49 ` Christoph Hellwig
2017-02-03 7:49 ` [lustre-devel] " Christoph Hellwig
2017-02-03 7:49 ` Christoph Hellwig
2017-02-03 8:54 ` Al Viro
2017-02-03 8:54 ` [lustre-devel] " Al Viro
2017-02-03 8:54 ` Al Viro
2017-02-03 11:09 ` Christoph Hellwig
2017-02-03 11:09 ` [lustre-devel] " Christoph Hellwig
2017-02-03 11:09 ` Christoph Hellwig
2017-02-02 14:48 ` Jan Kara
2017-02-02 14:48 ` [lustre-devel] " Jan Kara
2017-02-02 14:48 ` Jan Kara
2017-02-02 18:28 ` Al Viro
2017-02-02 18:28 ` [lustre-devel] " Al Viro
2017-02-02 18:28 ` Al Viro
2017-02-03 14:47 ` Jan Kara
2017-02-03 14:47 ` [lustre-devel] " Jan Kara
2017-02-03 14:47 ` Jan Kara
2017-02-04 3:08 ` Al Viro
2017-02-04 3:08 ` [lustre-devel] " Al Viro
2017-02-04 3:08 ` Al Viro
2017-02-04 19:26 ` Al Viro
2017-02-04 19:26 ` [lustre-devel] " Al Viro
2017-02-04 19:26 ` Al Viro
2017-02-04 22:12 ` Miklos Szeredi
2017-02-04 22:12 ` Miklos Szeredi
2017-02-04 22:11 ` Miklos Szeredi [this message]
2017-02-04 22:11 ` Miklos Szeredi
2017-02-05 1:51 ` Al Viro
2017-02-05 1:51 ` [lustre-devel] " Al Viro
2017-02-05 1:51 ` Al Viro
2017-02-05 20:15 ` Miklos Szeredi
2017-02-05 20:15 ` Miklos Szeredi
2017-02-05 21:01 ` Al Viro
2017-02-05 21:01 ` [lustre-devel] " Al Viro
2017-02-05 21:01 ` Al Viro
2017-02-05 21:19 ` Miklos Szeredi
2017-02-05 21:19 ` Miklos Szeredi
2017-02-05 22:04 ` Al Viro
2017-02-05 22:04 ` [lustre-devel] " Al Viro
2017-02-05 22:04 ` Al Viro
2017-02-05 22:04 ` Al Viro
2017-02-06 3:05 ` Al Viro
2017-02-06 3:05 ` [lustre-devel] " Al Viro
2017-02-06 3:05 ` Al Viro
2017-02-06 9:08 ` Miklos Szeredi
2017-02-06 9:57 ` Al Viro
2017-02-06 9:57 ` [lustre-devel] " Al Viro
2017-02-06 9:57 ` Al Viro
2017-02-06 14:18 ` Miklos Szeredi
2017-02-07 7:19 ` Al Viro
2017-02-07 7:19 ` [lustre-devel] " Al Viro
2017-02-07 7:19 ` Al Viro
2017-02-07 11:35 ` Miklos Szeredi
2017-02-07 11:35 ` Miklos Szeredi
2017-02-08 5:54 ` Al Viro
2017-02-08 5:54 ` [lustre-devel] " Al Viro
2017-02-08 5:54 ` Al Viro
2017-02-08 9:53 ` Miklos Szeredi
2017-02-06 8:37 ` Miklos Szeredi
2017-02-05 20:56 ` Al Viro
2017-02-05 20:56 ` [lustre-devel] " Al Viro
2017-02-05 20:56 ` Al Viro
2017-02-16 13:10 ` Jeff Layton
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