Date:	Mon, 27 Oct 2008 08:21:19 +0100
From:	Nadia Derbey <Nadia.Derbey@...l.net>
To:	cboulte@...il.com
Cc:	akpm@...ux-foundation.org, manfred@...orfullife.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] (v2) SYSVIPC - Fix the ipc structures
	initialization

On Fri, 2008-10-24 at 16:29 +0200, Nadia Derbey wrote:
> On Fri, 2008-10-24 at 16:05 +0200, cboulte@...il.com wrote:
> > On Fri, Oct 24, 2008 at 8:00 AM,  <Nadia.Derbey@...l.net> wrote:
> > >
> > > This patch is a fix for Bugzilla bug
> > > http://bugzilla.kernel.org/show_bug.cgi?id=11796.
> > >
> > > To summarize, a simple testcase is concurrently running an infinite loop on
> > > msgctl(IPC_STAT) and a call to msgget():
> > >
> > > while (1)
> > >   msgctl(id, IPC_STAT)    1
> > >                           |
> > >                           |
> > >                           |
> > >                           2 id = msgget(key, IPC_CREAT)
> > >                           |
> > >                           |
> > >                           |
> > >
> > > In the interval [1-2], the id doesn't exist yet.
> > >
> > > In that test, the problem is the following:
> > > When we are calling ipc_addid() from msgget() the msq structure is not
> > > completely initialized. So idr_get_new() is inserting a pointer into the
> > > idr tree, and the structure which is pointed to has, among other fields,
> > > its lock uninitialized.
> > >
> > > Since msgctl(IPC_STAT) is looping while (1), idr_find() returns the
> > > pointer as soon as it is inserted into the IDR tree. And ipc_lock()
> > > calls spin_lock(&mqs->lock), while we have not initialized that lock
> > > yet.
> > >
> > > This patch moves the spin_lock_init() before the call to ipc_addid().
> > > It also sets the "deleted" flag to 1 in the window between ipc structure
> > > allocation and its locking in ipc_addid().
> > >
> > > Regards,
> > > Nadia
> > >
> > >
> > > Signed-off-by: Nadia Derbey <Nadia.Derbey@...l.net>
> > >
> > > ---
> > >  ipc/util.c |   12 +++++++++++-
> > >  1 file changed, 11 insertions(+), 1 deletion(-)
> > >
> > > Index: linux-2.6.27/ipc/util.c
> > > ===================================================================
> > > --- linux-2.6.27.orig/ipc/util.c        2008-10-23 15:20:46.000000000 +0200
> > > +++ linux-2.6.27/ipc/util.c     2008-10-24 09:03:06.000000000 +0200
> > > @@ -266,6 +266,17 @@ int ipc_addid(struct ipc_ids* ids, struc
> > >        if (ids->in_use >= size)
> > >                return -ENOSPC;
> > >
> > > +       spin_lock_init(&new->lock);
> > > +
> > > +       /*
> > > +        * We have a window between the time new is inserted into the idr
> > > +        * tree and the time it is actually locked.
> > > +        * In order to be safe during that window set the new ipc structure
> > > +        * as deleted: a concurrent ipc_lock() will see it as not present
> > > +        * until the initialization phase is complete.
> > > +        */
> > > +       new->deleted = 1;
> > > +
> > >        err = idr_get_new(&ids->ipcs_idr, new, &id);
> > >        if (err)
> > >                return err;
> > > @@ -280,7 +291,6 @@ int ipc_addid(struct ipc_ids* ids, struc
> > >                ids->seq = 0;
> > >
> > >        new->id = ipc_buildid(id, new->seq);
> > > -       spin_lock_init(&new->lock);
> > >        new->deleted = 0;
> > >        rcu_read_lock();
> > >        spin_lock(&new->lock);
> > >
> > > --
> > >
> > 
> > I tried the test with your patch (on a 2.6.27), and got a soft lockup
> > again (the test ran during 5 minutes).
> 
> Well, it has been running for much much more than 5 minutes on my
> victim...
> 
> >  It was harder to reproduce (it
> > took longer) but still there. Output:
> > 
> > [ 1476.099160] INFO: trying to register non-static key.
> > [ 1476.100507] the code is fine but needs lockdep annotation.
> > [ 1476.100507] turning off the locking correctness validator.
> > [ 1476.100507] Pid: 3082, comm: sysv_test2 Not tainted 2.6.27-ipc_lock #6
> > [ 1476.100507]
> > [ 1476.100507] Call Trace:
> > [ 1476.100507]  [<ffffffff802585d2>] static_obj+0x51/0x68
> > [ 1476.100507]  [<ffffffff8025b913>] __lock_acquire+0xe0a/0x153a
> > [ 1476.100507]  [<ffffffff8020c83e>] restore_args+0x0/0x30
> > [ 1476.100507]  [<ffffffff80212dd1>] sched_clock+0x5/0x7
> > [ 1476.100507]  [<ffffffff8025c0d8>] lock_acquire+0x95/0xc2
> > [ 1476.100507]  [<ffffffff803036aa>] ipc_lock+0x63/0x9b
> > [ 1476.100507]  [<ffffffff80459c77>] _spin_lock+0x2d/0x59
> > [ 1476.100507]  [<ffffffff803036aa>] ipc_lock+0x63/0x9b
> > [ 1476.100507]  [<ffffffff803036aa>] ipc_lock+0x63/0x9b
> > [ 1476.100507]  [<ffffffff80303647>] ipc_lock+0x0/0x9b
> > [ 1476.100507]  [<ffffffff803036ee>] ipc_lock_check+0xc/0x57
> > [ 1476.100507]  [<ffffffff80304ac9>] sys_msgctl+0x18e/0x502
> > [ 1476.100507]  [<ffffffff8045786c>] thread_return+0x3d/0xbe
> > [ 1476.100507]  [<ffffffff80255e3c>] tick_dev_program_event+0x2d/0x95
> > [ 1476.100507]  [<ffffffff804596dd>] trace_hardirqs_on_thunk+0x3a/0x3f
> > [ 1476.100507]  [<ffffffff8025a201>] trace_hardirqs_on_caller+0xff/0x12a
> > [ 1476.100507]  [<ffffffff804596dd>] trace_hardirqs_on_thunk+0x3a/0x3f
> > [ 1476.100507]  [<ffffffff8025a201>] trace_hardirqs_on_caller+0xff/0x12a
> > [ 1476.100507]  [<ffffffff804596dd>] trace_hardirqs_on_thunk+0x3a/0x3f
> > [ 1476.100507]  [<ffffffff80212dd1>] sched_clock+0x5/0x7
> > [ 1476.100507]  [<ffffffff8020bfca>] system_call_fastpath+0x16/0x1b
> > [ 1476.100507]
> > [ 1540.820503] BUG: soft lockup - CPU#1 stuck for 61s! [sysv_test2:3082]
> > [ 1540.820506] Modules linked in: autofs4 video output ac battery ipv6
> > nfs lockd nfs_acl sunrpc dm_snapshot dm_mirror dm_log dm_mod loop
> > snd_pcsp snd_pcm snd_timer snd soundcore snd_page_alloc i2c_i801
> > rng_core serio_raw i2c_core psmouse iTCO_wdt shpchp pci_hotplug button
> > e752x_edac edac_core joydev evdev ext3 jbd mbcache sd_mod sg sr_mod
> > cdrom ata_generic usbhid hid ff_memless ata_piix libata dock mptspi
> > mptscsih mptbase ide_pci_generic scsi_transport_spi uhci_hcd ehci_hcd
> > ide_core tg3 scsi_mod libphy thermal processor fan thermal_sys
> > [ 1540.820506] irq event stamp: 2117257
> > [ 1540.820506] hardirqs last  enabled at (2117257):
> > [<ffffffff804596dd>] trace_hardirqs_on_thunk+0x3a/0x3f
> > [ 1540.820506] hardirqs last disabled at (2117256):
> > [<ffffffff8045971c>] trace_hardirqs_off_thunk+0x3a/0x3c
> > [ 1540.820506] softirqs last  enabled at (2111724):
> > [<ffffffff8020da0c>] call_softirq+0x1c/0x28
> > [ 1540.820506] softirqs last disabled at (2111719):
> > [<ffffffff8020da0c>] call_softirq+0x1c/0x28
> > [ 1540.820506] CPU 1:
> > [ 1540.820506] Modules linked in: autofs4 video output ac battery ipv6
> > nfs lockd nfs_acl sunrpc dm_snapshot dm_mirror dm_log dm_mod loop
> > snd_pcsp snd_pcm snd_timer snd soundcore snd_page_alloc i2c_i801
> > rng_core serio_raw i2c_core psmouse iTCO_wdt shpchp pci_hotplug button
> > e752x_edac edac_core joydev evdev ext3 jbd mbcache sd_mod sg sr_mod
> > cdrom ata_generic usbhid hid ff_memless ata_piix libata dock mptspi
> > mptscsih mptbase ide_pci_generic scsi_transport_spi uhci_hcd ehci_hcd
> > ide_core tg3 scsi_mod libphy thermal processor fan thermal_sys
> > [ 1540.820506] Pid: 3082, comm: sysv_test2 Not tainted 2.6.27-ipc_lock #6
> > [ 1540.820506] RIP: 0010:[<ffffffff80213529>]  [<ffffffff80213529>]
> > native_read_tsc+0x8/0x1d
> > [ 1540.820506] RSP: 0018:ffff8801458c1db8  EFLAGS: 00000286
> > [ 1540.820506] RAX: 0000000050aadc78 RBX: ffff88014452fb70 RCX: 0000000050aadb8a
> > [ 1540.820506] RDX: 0000000000000446 RSI: ffffffff805425bc RDI: 0000000000000001
> > [ 1540.820506] RBP: 0000000000000000 R08: 0000000000000002 R09: 0000000000000000
> > [ 1540.820506] R10: ffffffff80250954 R11: ffffffff8033fa39 R12: ffff88002f312160
> > [ 1540.820506] R13: ffff8800aeae6000 R14: ffff8801458c0000 R15: ffffffff8082c810
> > [ 1540.820506] FS:  00007ffbced256e0(0000) GS:ffff880147054d18(0000)
> > knlGS:0000000000000000
> > [ 1540.820506] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > [ 1540.820506] CR2: 00007ffbce890c70 CR3: 0000000144d05000 CR4: 00000000000006e0
> > [ 1540.820506] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [ 1540.820506] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > [ 1540.820506]
> > [ 1540.820506] Call Trace:
> > [ 1540.820506]  [<ffffffff8033fa51>] delay_tsc+0x18/0x51
> > [ 1540.820506]  [<ffffffff80220ebd>] __ticket_spin_trylock+0x5/0x18
> > [ 1540.820506]  [<ffffffff8034301b>] _raw_spin_lock+0x96/0x102
> > [ 1540.820506]  [<ffffffff80459c98>] _spin_lock+0x4e/0x59
> > [ 1540.820506]  [<ffffffff803036aa>] ipc_lock+0x63/0x9b
> > [ 1540.820506]  [<ffffffff803036aa>] ipc_lock+0x63/0x9b
> > [ 1540.820506]  [<ffffffff80303647>] ipc_lock+0x0/0x9b
> > [ 1540.820506]  [<ffffffff803036ee>] ipc_lock_check+0xc/0x57
> > [ 1540.820506]  [<ffffffff80304ac9>] sys_msgctl+0x18e/0x502
> > [ 1540.820506]  [<ffffffff8045786c>] thread_return+0x3d/0xbe
> > [ 1540.820506]  [<ffffffff80255e3c>] tick_dev_program_event+0x2d/0x95
> > [ 1540.820506]  [<ffffffff804596dd>] trace_hardirqs_on_thunk+0x3a/0x3f
> > [ 1540.820506]  [<ffffffff8025a201>] trace_hardirqs_on_caller+0xff/0x12a
> > [ 1540.820506]  [<ffffffff804596dd>] trace_hardirqs_on_thunk+0x3a/0x3f
> > [ 1540.820506]  [<ffffffff8025a201>] trace_hardirqs_on_caller+0xff/0x12a
> > [ 1540.820506]  [<ffffffff804596dd>] trace_hardirqs_on_thunk+0x3a/0x3f
> > [ 1540.820506]  [<ffffffff80212dd1>] sched_clock+0x5/0x7
> > [ 1540.820506]  [<ffffffff8020bfca>] system_call_fastpath+0x16/0x1b
> > [ 1540.820506]
> > [ 1606.320502] BUG: soft lockup - CPU#1 stuck for 61s
> > 
> > Inspired by your patch I wrote this one on top of yours:
> > ---
> >  ipc/util.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > Index: bug-sysv/ipc/util.c
> > ===================================================================
> > --- bug-sysv.orig/ipc/util.c
> > +++ bug-sysv/ipc/util.c
> > @@ -267,6 +267,8 @@ int ipc_addid(struct ipc_ids* ids, struc
> >                 return -ENOSPC;
> > 
> >         spin_lock_init(&new->lock);
> > +       rcu_read_lock();
> > +       spin_lock(&new->lock);
> > 
> >         /*
> >          * We have a window between the time new is inserted into the idr
> > @@ -292,8 +294,6 @@ int ipc_addid(struct ipc_ids* ids, struc
> > 
> >         new->id = ipc_buildid(id, new->seq);
> >         new->deleted = 0;
> > -       rcu_read_lock();
> > -       spin_lock(&new->lock);
> >         return id;
> >  }
> > 
> > And I don't see any soft lockup for the moment (the test runs during
> > 30 minutes). But I'm far from being confidant about this code. I'm
> > just surprise that new is inserted into the list without all its
> > attributes initialized.
> 
> Well, the fields we need to be initialized when new is inserted into the
> list are 1. its lock 2. the deleted field: prior to any access,
> ipc_lock / ipc_lock_check will be called and they need these 2 fields.
> 
> >  Besides, assiging new->delete = 0 without
> > locking the ipc seems strange.
> 
> Oh oh! I missed that one. It's true that it should be done after taking
> the lock. 
> 
> Will run the test with my patch + ->deleted=0 after taking the lock
> during the whole week-end, and let you know.
> 

OK, it has been running during the week-end, without any problem.
Resending the patch right now.

Regards,
Nadia

-- 
Nadia Derbey <Nadia.Derbey@...l.net>

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