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Date: Wed, 9 Mar 2005 11:42:34 -0800
From: Andrew Morton <akpm@osdl.org>
To: Badari Pulavarty <pbadari@us.ibm.com>
Cc: dhowells@redhat.com, torvalds@osdl.org, arjan@infradead.org,
       suparna@in.ibm.com, linux-aio@kvack.org, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH] rwsem: Make rwsems use interrupt disabling spinlocks
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Badari Pulavarty <pbadari@us.ibm.com> wrote:
>
>  I am not sure if this is related to your patch. But I ran into
>  BUG() with sysrq-t with your patch.
> 
>  Thanks,
>  Badari
> 
>  BUG: soft lockup detected on CPU#1!
>                                      
>  Modules linked in: joydev sg st floppy usbserial parport_pc lp parport
>  ipv6 ohci_hcd i2c_amd756 i2c_core evdev usbcore raid0 dm_mod nls_utf8
>  Pid: 15433, comm: bash Not tainted 2.6.11-mm1n
>  RIP: 0010:[<ffffffff8013d094>] <ffffffff8013d094>{__do_softirq+84}
>  RSP: 0018:ffff8101dff83f68  EFLAGS: 00000206
>  RAX: ffffffff80651880 RBX: 0000000000000002 RCX: 0000000000000004
>  RDX: 0000000000000002 RSI: 0000000000000103 RDI: ffff8101d7c77680
>  RBP: ffff810177ffbe48 R08: 0000000000000002 R09: 0000000000000100
>  R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000001
>  R13: 00002aaaaaafb000 R14: 000000000000000a R15: 0000000000000001
>  FS:  00002aaaab2890a0(0000) GS:ffffffff80651880(0000)
>  knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>  CR2: 00002aaaaaafb000 CR3: 00000001bb2a0000 CR4: 00000000000006e0
>                                                                    
>  Call Trace:<IRQ> <ffffffff8013d165>{do_softirq+53}
>  <ffffffff8010ef59>{apic_timer_interrupt+133}
>          <EOI> <ffffffff80403055>{_spin_unlock_irqrestore+5}
>         <ffffffff801bd357>{write_sysrq_trigger+55}
>  <ffffffff80183579>{vfs_write+233}
>         <ffffffff80183713>{sys_write+83}
>  <ffffffff8010e5ce>{system_call+126}

That's probably just a false positive in Ingo's soft-lockup detector.  Long
streams of irq-context serial console output will do that.

Ingo, we already have a touch_nmi_watchdog() in the sysrq code.  It might be
worth adding a touch_softlockup_watchdog() wherever we have a
touch_nmi_watchdog().