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Date: Wed, 13 Aug 2008 03:29:46 -0700 (PDT) From: David Miller <davem@...emloft.net> To: adobriyan@...il.com Cc: vegard.nossum@...il.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, jgarzik@...ox.com Subject: Re: [RFC][PATCH] netconsole: avoid deadlock on printk from driver code From: Alexey Dobriyan <adobriyan@...il.com> Date: Wed, 13 Aug 2008 13:59:43 +0400 > On Wed, Aug 13, 2008 at 11:53:24AM +0200, Vegard Nossum wrote: > > I encountered a hard-to-debug deadlock when I pulled out the plug of my > > RealTek 8139 which was also running netconsole: The driver wants to print > > a "link down" message. However, this triggers netconsole, which wants to > > print the message using the same device. Here is a backtrace: > > > > [<c05916b6>] _spin_lock_irqsave+0x76/0x90 > > [<c035b255>] rtl8139_start_xmit+0x65/0x130 <-- spin_lock(&tp->lock) > > [<c04c5e28>] netpoll_send_skb+0x158/0x1a0 > > [<c04c62fb>] netpoll_send_udp+0x1db/0x1f0 > > [<c037c70c>] write_msg+0x8c/0xc0 > > [<c0135883>] __call_console_drivers+0x53/0x60 > > [<c01358db>] _call_console_drivers+0x4b/0x90 > > [<c0135a25>] release_console_sem+0xc5/0x1f0 > > [<c0135f0b>] vprintk+0x1ab/0x3e0 > > [<c013615b>] printk+0x1b/0x20 > > [<c0349736>] mii_check_media+0x196/0x1e0 > > [<c03597f4>] rtl_check_media+0x24/0x30 > > [<c035a0ea>] rtl8139_interrupt+0x42a/0x4a0 <-- spin_lock(&tp->lock) > > [<c01716d8>] handle_IRQ_event+0x28/0x70 > > [<c0172d9b>] handle_fasteoi_irq+0x6b/0xe0 > > [<c0107128>] do_IRQ+0x48/0xa0 > > > > The least invasive fix is to detect that we're trying to re-enter the > > driver code. We provide a netdev_busy() function which can be used to > > determine whether a deadlock can occur if we try to transmit another > > packet. > > > > Note that this may lead to lost messages if the driver is active on > > another CPU while we try to use the same device for netconsole. > > This sucks. It's also the wrong fix. As a quicker and more palatable solution, print your link status message in some kind of deferred context where you can have the lock not held or similar. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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