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Date: Sun, 1 Jul 2007 21:35:58 +0400 From: Oleg Nesterov <oleg@...sign.ru> To: Jarek Poplawski <jarkao2@...pl>, Linus Torvalds <torvalds@...ux-foundation.org> Cc: Andrew Morton <akpm@...ux-foundation.org>, "David S. Miller" <davem@...emloft.net>, linux-kernel@...r.kernel.org Subject: Re: [NETPOLL] netconsole: fix soft lockup when removing module Jarek Poplawski wrote: > > #1 > Until kernel ver. 2.6.21 (including) cancel_rearming_delayed_work() > required a work function should always (unconditionally) rearm with > delay > 0 - otherwise it would endlessly loop. This patch replaces > this function with cancel_delayed_work(). Later kernel versions don't > require this, so here it's only for uniformity. But 2.6.22 doesn't need this change, why it was merged? In fact, I suspect this change adds a race, > --- a/net/core/netpoll.c > +++ b/net/core/netpoll.c > @@ -72,7 +72,8 @@ static void queue_process(struct work_struct *work) > netif_tx_unlock(dev); > local_irq_restore(flags); > > - schedule_delayed_work(&npinfo->tx_work, HZ/10); > + if (atomic_read(&npinfo->refcnt)) > + schedule_delayed_work(&npinfo->tx_work, HZ/10); > return; > } > netif_tx_unlock(dev); > @@ -785,9 +786,15 @@ void netpoll_cleanup(struct netpoll *np) > if (atomic_dec_and_test(&npinfo->refcnt)) { > skb_queue_purge(&npinfo->arp_tx); > skb_queue_purge(&npinfo->txq); > - cancel_rearming_delayed_work(&npinfo->tx_work); > + cancel_delayed_work(&npinfo->tx_work); > flush_scheduled_work(); Suppose that ->refcnt == 1, and queue_process() was preempted just after atomic_read(&npinfo->refcnt). netpoll_cleanup() comes, cancel_delayed_work() does nothing, flush_scheduled_work() sleeps. queue_process() gets CPU, re-schedules ->tx_work, and returns. flush_scheduled_work() completes, netpoll_cleanup() frees npinfo and returns while ->tx_work is pending. No? Oleg. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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