Messages in this thread | | | Date | Wed, 21 Mar 2007 09:05:10 +0100 | From | Jarek Poplawski <> | Subject | Re: [PATCH] Re: [2.6.20] BUG: workqueue leaked lock |
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On Tue, Mar 20, 2007 at 07:07:59PM +0300, Oleg Nesterov wrote: > On 03/20, Jarek Poplawski wrote: ... > > >>> On Thu, 2007-03-15 at 11:06 -0800, Andrew Morton wrote: > > >>>>> On Tue, 13 Mar 2007 17:50:14 +0100 Folkert van Heusden <folkert@vanheusden.com> wrote: > > >>>>> ... > > >>>>> [ 1756.728209] BUG: workqueue leaked lock or atomic: nfsd4/0x00000000/3577 > > >>>>> [ 1756.728271] last function: laundromat_main+0x0/0x69 [nfsd] > > >>>>> [ 1756.728392] 2 locks held by nfsd4/3577: > > >>>>> [ 1756.728435] #0: (client_mutex){--..}, at: [<c1205b88>] mutex_lock+0x8/0xa > > >>>>> [ 1756.728679] #1: (&inode->i_mutex){--..}, at: [<c1205b88>] mutex_lock+0x8/0xa > > >>>>> [ 1756.728923] [<c1003d57>] show_trace_log_lvl+0x1a/0x30 > > >>>>> [ 1756.729015] [<c1003d7f>] show_trace+0x12/0x14 > > >>>>> [ 1756.729103] [<c1003e79>] dump_stack+0x16/0x18 > > >>>>> [ 1756.729187] [<c102c2e8>] run_workqueue+0x167/0x170 > > >>>>> [ 1756.729276] [<c102c437>] worker_thread+0x146/0x165 > > >>>>> [ 1756.729368] [<c102f797>] kthread+0x97/0xc4 > > >>>>> [ 1756.729456] [<c1003bdb>] kernel_thread_helper+0x7/0x10 > > >>>>> [ 1756.729547] ======================= ... > > This check is valid with keventd, but it looks like nfsd runs > > kthread by itself. I'm not sure it's illegal to hold locks then, > > nfsd creates laundry_wq by itself, yes, but cwq->thread runs with > lockdep_depth() == 0. Unless we have a bug with lockdep_depth(), > lockdep_depth() != 0 means that work->func() returns with a lock > held (or it can flush its own workqueue under lock, but in that case > we should have a different trace).
IMHO you can only say this thread is supposed to run with lockdep_depth() == 0. lockdep_depth is counted within a process, which starts before f(), so the only way to say f() leaked locks is to check these locks before and after f().
> > Personally I agree with Andrew: > > > > > OK. That's not necessarily a bug: one could envisage a (weird) piece of > > > code which takes a lock then releases it on a later workqueue invokation.
But this code is named here as laundromat_main and it doesn't seem to work like this.
> > > @@ -323,13 +324,15 @@ static void run_workqueue(struct cpu_wor > > BUG_ON(get_wq_data(work) != cwq); > > if (!test_bit(WORK_STRUCT_NOAUTOREL, work_data_bits(work))) > > work_release(work); > > + ld = lockdep_depth(current); > > + > > f(work); > > > > - if (unlikely(in_atomic() || lockdep_depth(current) > 0)) { > > + if (unlikely(in_atomic() || (ld -= lockdep_depth(current)))) { > > and with this change we will also have a BUG report on "then releases it on a > later workqueue invokation".
Then we could say at least this code is weird (buggy - in my opinion). This patch doesn't change the way the "standard" code is treated, so I cannot see any possibility to get it worse then now.
Regards, Jarek P. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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