lkml.org 
[lkml]   [2019]   [Jan]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] libceph: protect pending flags in ceph_con_keepalive()
On Mon, Jan 14, 2019 at 09:37:25PM +0100, Ilya Dryomov wrote:
> On Thu, Jan 3, 2019 at 4:50 AM Myungho Jung <mhjungk@gmail.com> wrote:
> > I reproduced on vm using syzkaller utils and verified the fix by syzbot.
>
> Hi Myungho,
>
> I think this might be a better fix:
>
> diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
> index d5718284db57..c5f5313e3537 100644
> --- a/net/ceph/messenger.c
> +++ b/net/ceph/messenger.c
> @@ -3205,10 +3205,11 @@ void ceph_con_keepalive(struct ceph_connection *con)
> {
> dout("con_keepalive %p\n", con);
> mutex_lock(&con->mutex);
> + con_flag_set(con, CON_FLAG_KEEPALIVE_PENDING);
> clear_standby(con);
> mutex_unlock(&con->mutex);
> - if (con_flag_test_and_set(con, CON_FLAG_KEEPALIVE_PENDING) == 0 &&
> - con_flag_test_and_set(con, CON_FLAG_WRITE_PENDING) == 0)
> +
> + if (con_flag_test_and_set(con, CON_FLAG_WRITE_PENDING) == 0)
> queue_con(con);
> }
> EXPORT_SYMBOL(ceph_con_keepalive);
>
> WRITE_PENDING can be set without con->mutex held from socket callbacks.
> This is the reason we use atomic bit ops here, so testing WRITE_PENDING
> under the lock didn't make sense to me.
>
> At the same time, KEEPALIVE_PENDING could have been a non-atomic flag.
> I spent some time trying to make sense of conditioning queue_con() call
> on the previous value of KEEPALIVE_PENDING and couldn't see any, so I'm
> setting it with con_flag_set(), making ceph_con_keepalive() symmetric
> with ceph_con_send().
>
> Thanks,
>
> Ilya

Hi Ilya,

Yes, it looks clear and makes sense to have an atomic operation in if statement
but it still triggers warning. KEEPALIVE_PENDING should be set after
clear_standby() because con_fault() can be called right before acquiring the
lock here which sets the flag in standby state. I tesed the change with syzbot
and confirmed there was no warning.

Thanks,
Myungho

\
 
 \ /
  Last update: 2019-01-15 07:56    [W:0.074 / U:7.748 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site