From mboxrd@z Thu Jan  1 00:00:00 1970
From: Juergen Gross <juergen.gross@ts.fujitsu.com>
Subject: Re: [RFC/RFT][PATCH 0 of 3] rework locking
	in	sched_adjust
Date: Tue, 06 Dec 2011 13:39:27 +0100
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To: George Dunlap <George.Dunlap@eu.citrix.com>
Cc: Dario Faggioli <raistlin@linux.it>, xen-devel@lists.xensource.com, Keir Fraser <keir@xen.org>
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On 12/06/2011 01:30 PM, George Dunlap wrote:
> On Tue, Dec 6, 2011 at 8:38 AM, Juergen Gross
> <juergen.gross@ts.fujitsu.com>  wrote:
>> (XEN) Xen BUG at spinlock.c:47
> [snip]
>> (XEN) Xen call trace:
>> (XEN)    [<ffff82c480124e84>] check_lock+0x44/0x50
>> (XEN)    [<ffff82c480124ec1>] _spin_lock+0x11/0x5d
>> (XEN)    [<ffff82c48012c085>] xmem_pool_alloc+0x138/0x4d2
>> (XEN)    [<ffff82c48012c557>] _xmalloc+0x138/0x230
>> (XEN)    [<ffff82c48012c660>] _xzalloc+0x11/0x2d
>> (XEN)    [<ffff82c48011f8ab>] sedf_adjust+0x37c/0x9b2
>> (XEN)    [<ffff82c480120fec>] sched_adjust+0x5f/0xb7
>> (XEN)    [<ffff82c4801037e3>] do_domctl+0xf32/0x1a9f
>> (XEN)    [<ffff82c48021f128>] syscall_enter+0xc8/0x122
> Hmm, looks like the problem is that we assert that locks must be
> called with IRQs enabled all the time, or never.  From
> xen/common/spinlock.c:
>
>       * We partition locks into IRQ-safe (always held with IRQs disabled) and
>       * IRQ-unsafe (always held with IRQs enabled) types. The convention for
>       * every lock must be consistently observed else we can deadlock in
>       * IRQ-context rendezvous functions (a rendezvous which gets every CPU
>       * into IRQ context before any CPU is released from the rendezvous).
>
> sedf_adj() grabs the private lock with irqs disabled, then calls
> sedf_adjust_weights(), which calls xmalloc to allocate some local
> scratch space, which ultimately grabs a non-IRQ spinlock.
>
> Not sure the best thing to do here...
sedf_adjust_weights() is called only from sedf_adj(). The easiest solution
would be to xmalloc the scratch space in sedf_adj() before grabbing the lock
and passing the xmalloced area to sedf_adjust_weights().


Juergen

-- 
Juergen Gross                 Principal Developer Operating Systems
PDG ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@ts.fujitsu.com
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