netdev - Re: [PATCH 1/2] drop_monitor: fix sleeping in invalid context warning

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Date:	Thu, 26 Apr 2012 15:21:48 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>
Subject: Re: [PATCH 1/2] drop_monitor: fix sleeping in invalid context warning

On Thu, Apr 26, 2012 at 09:01:29PM +0200, Eric Dumazet wrote:
> On Thu, 2012-04-26 at 14:47 -0400, Neil Horman wrote:
> > Eric Dumazet pointed out this warning in the drop_monitor protocol to me:
> > 
> > [   38.352571] BUG: sleeping function called from invalid context at kernel/mutex.c:85
> > [   38.352576] in_atomic(): 1, irqs_disabled(): 0, pid: 4415, name: dropwatch
> > [   38.352580] Pid: 4415, comm: dropwatch Not tainted 3.4.0-rc2+ #71
> > [   38.352582] Call Trace:
> > [   38.352592]  [<ffffffff8153aaf0>] ? trace_napi_poll_hit+0xd0/0xd0
> > [   38.352599]  [<ffffffff81063f2a>] __might_sleep+0xca/0xf0
> > [   38.352606]  [<ffffffff81655b16>] mutex_lock+0x26/0x50
> > [   38.352610]  [<ffffffff8153aaf0>] ? trace_napi_poll_hit+0xd0/0xd0
> > [   38.352616]  [<ffffffff810b72d9>] tracepoint_probe_register+0x29/0x90
> > [   38.352621]  [<ffffffff8153a585>] set_all_monitor_traces+0x105/0x170
> > [   38.352625]  [<ffffffff8153a8ca>] net_dm_cmd_trace+0x2a/0x40
> > [   38.352630]  [<ffffffff8154a81a>] genl_rcv_msg+0x21a/0x2b0
> > [   38.352636]  [<ffffffff810f8029>] ? zone_statistics+0x99/0xc0
> > [   38.352640]  [<ffffffff8154a600>] ? genl_rcv+0x30/0x30
> > [   38.352645]  [<ffffffff8154a059>] netlink_rcv_skb+0xa9/0xd0
> > [   38.352649]  [<ffffffff8154a5f0>] genl_rcv+0x20/0x30
> > [   38.352653]  [<ffffffff81549a7e>] netlink_unicast+0x1ae/0x1f0
> > [   38.352658]  [<ffffffff81549d76>] netlink_sendmsg+0x2b6/0x310
> > [   38.352663]  [<ffffffff8150824f>] sock_sendmsg+0x10f/0x130
> > [   38.352668]  [<ffffffff8150abe0>] ? move_addr_to_kernel+0x60/0xb0
> > [   38.352673]  [<ffffffff81515f04>] ? verify_iovec+0x64/0xe0
> > [   38.352677]  [<ffffffff81509c46>] __sys_sendmsg+0x386/0x390
> > [   38.352682]  [<ffffffff810ffaf9>] ? handle_mm_fault+0x139/0x210
> > [   38.352687]  [<ffffffff8165b5bc>] ? do_page_fault+0x1ec/0x4f0
> > [   38.352693]  [<ffffffff8106ba4d>] ? set_next_entity+0x9d/0xb0
> > [   38.352699]  [<ffffffff81310b49>] ? tty_ldisc_deref+0x9/0x10
> > [   38.352703]  [<ffffffff8106d363>] ? pick_next_task_fair+0x63/0x140
> > [   38.352708]  [<ffffffff8150b8d4>] sys_sendmsg+0x44/0x80
> > [   38.352713]  [<ffffffff8165f8e2>] system_call_fastpath+0x16/0x1b
> > 
> > It stems from holding a spinlock (trace_state_lock) while attempting to register
> > or unregister tracepoint hooks, making in_atomic() true in this context, leading
> > to the warning when the tracepoint calls might_sleep() while its taking a mutex.
> > Since we only use the trace_state_lock to prevent trace protocol state races, as
> > well as hardware stat list updates on an rcu write side, we can just convert the
> > spinlock to a mutex to avoid this problem.
> > 
> > Signed-off-by: Neil Horman <nhorman@...driver.com>
> > Reported-by: Eric Dumazet <eric.dumazet@...il.com>
> > CC: David Miller <davem@...emloft.net>
> > ---
> >  net/core/drop_monitor.c |   14 +++++++-------
> >  1 files changed, 7 insertions(+), 7 deletions(-)
> > 
> > diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
> > index 5c3c81a..04ce1dd 100644
> > --- a/net/core/drop_monitor.c
> > +++ b/net/core/drop_monitor.c
> > @@ -42,7 +42,7 @@ static void send_dm_alert(struct work_struct *unused);
> >   * netlink alerts
> >   */
> >  static int trace_state = TRACE_OFF;
> > -static DEFINE_SPINLOCK(trace_state_lock);
> > +static DEFINE_MUTEX(trace_state_lock);
> 
> Maybe rename it to trace_state_mutex ?
> 

ACK, no problem
> 
> 
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