[PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Leon Romanovsky]

From: Leon Romanovsky <leonro@mellanox.com>

The below kernel panic was observed when created bond mode LACP
with GRE tunnel on top. The reason to it was not released spinlock
during mlx5 notify unregsiter sequence.

[  234.562007] BUG: scheduling while atomic: sh/10900/0x00000002
[  234.563005] Preemption disabled at:
[  234.566864] ------------[ cut here ]------------
[  234.567120] DEBUG_LOCKS_WARN_ON(val > preempt_count())
[  234.567139] WARNING: CPU: 16 PID: 10900 at kernel/sched/core.c:3203 preempt_count_sub+0xca/0x170
[  234.569550] CPU: 16 PID: 10900 Comm: sh Tainted: G        W 5.2.0-rc1-for-linust-dbg-2019-05-25_04-57-33-60 #1
[  234.569886] Hardware name: Dell Inc. PowerEdge R720/0X3D66, BIOS 2.6.1 02/12/2018
[  234.570183] RIP: 0010:preempt_count_sub+0xca/0x170
[  234.570404] Code: 03 38
d0 7c 08 84 d2 0f 85 b0 00 00 00 8b 15 dd 02 03 04 85 d2 75 ba 48 c7 c6
00 e1 88 83 48 c7 c7 40 e1 88 83 e8 76 11 f7 ff <0f> 0b 5b c3 65 8b 05
d3 1f d8 7e 84 c0 75 82 e8 62 c3 c3 00 85 c0
[  234.570911] RSP: 0018:ffff888b94477b08 EFLAGS: 00010286
[  234.571133] RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
[  234.571391] RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000246
[  234.571648] RBP: ffff888ba5560000 R08: fffffbfff08962d5 R09: fffffbfff08962d5
[  234.571902] R10: 0000000000000001 R11: fffffbfff08962d4 R12: ffff888bac6e9548
[  234.572157] R13: ffff888babfaf728 R14: ffff888bac6e9568 R15: ffff888babfaf750
[  234.572412] FS: 00007fcafa59b740(0000) GS:ffff888bed200000(0000) knlGS:0000000000000000
[  234.572686] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  234.572914] CR2: 00007f984f16b140 CR3: 0000000b2bf0a001 CR4: 00000000001606e0
[  234.573172] Call Trace:
[  234.573336] _raw_spin_unlock+0x2e/0x50
[  234.573542] mlx5_ib_unbind_slave_port+0x1bc/0x690 [mlx5_ib]
[  234.573793] mlx5_ib_cleanup_multiport_master+0x1d3/0x660 [mlx5_ib]
[  234.574039] mlx5_ib_stage_init_cleanup+0x4c/0x360 [mlx5_ib]
[  234.574271]  ? kfree+0xf5/0x2f0
[  234.574465] __mlx5_ib_remove+0x61/0xd0 [mlx5_ib]
[  234.574688]  ? __mlx5_ib_remove+0xd0/0xd0 [mlx5_ib]
[  234.574951] mlx5_remove_device+0x234/0x300 [mlx5_core]
[  234.575224] mlx5_unregister_device+0x4d/0x1e0 [mlx5_core]
[  234.575493] remove_one+0x4f/0x160 [mlx5_core]
[  234.575704] pci_device_remove+0xef/0x2a0
[  234.581407]  ? pcibios_free_irq+0x10/0x10
[  234.587143]  ? up_read+0xc1/0x260
[  234.592785] device_release_driver_internal+0x1ab/0x430
[  234.598442] unbind_store+0x152/0x200
[  234.604064]  ? sysfs_kf_write+0x3b/0x180
[  234.609441]  ? sysfs_file_ops+0x160/0x160
[  234.615021] kernfs_fop_write+0x277/0x440
[  234.620288]  ? __sb_start_write+0x1ef/0x2c0
[  234.625512] vfs_write+0x15e/0x460
[  234.630786] ksys_write+0x156/0x1e0
[  234.635988]  ? __ia32_sys_read+0xb0/0xb0
[  234.641120]  ? trace_hardirqs_off_thunk+0x1a/0x1c
[  234.646163] do_syscall_64+0x95/0x470
[  234.651106] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[  234.656004] RIP: 0033:0x7fcaf9c9cfd0
[  234.660686] Code: 73 01
c3 48 8b 0d c0 6e 2d 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00
83 3d cd cf 2d 00 00 75 10 b8 01 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73
31 c3 48 83 ec 08 e8 ee cb 01 00 48 89 04 24
[  234.670128] RSP: 002b:00007ffd3b01ddd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[  234.674811] RAX: ffffffffffffffda RBX: 000000000000000d RCX: 00007fcaf9c9cfd0
[  234.679387] RDX: 000000000000000d RSI: 00007fcafa5c1000 RDI: 0000000000000001
[  234.683848] RBP: 00007fcafa5c1000 R08: 000000000000000a R09: 00007fcafa59b740
[  234.688167] R10: 00007ffd3b01d8e0 R11: 0000000000000246 R12: 00007fcaf9f75400
[  234.692386] R13: 000000000000000d R14: 0000000000000001 R15: 0000000000000000
[  234.696495] irq event stamp: 153067
[  234.700525] hardirqs last enabled at (153067): [<ffffffff83258c39>] _raw_spin_unlock_irqrestore+0x59/0x70
[  234.704665] hardirqs last disabled at (153066): [<ffffffff83259382>] _raw_spin_lock_irqsave+0x22/0x90
[  234.708722] softirqs last enabled at (153058): [<ffffffff836006c5>] __do_softirq+0x6c5/0xb4e
[  234.712673] softirqs last disabled at (153051): [<ffffffff81227c1d>] irq_exit+0x17d/0x1d0
[  234.716601] ---[ end trace 5dbf096843ee9ce6 ]---

Fixes: df097a278c75 ("IB/mlx5: Use the new mlx5 core notifier API")
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
---
 drivers/infiniband/hw/mlx5/main.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index c2a5780cb394..e12a4404096b 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -5802,13 +5802,12 @@ static void mlx5_ib_unbind_slave_port(struct mlx5_ib_dev *ibdev,
 		return;
 	}
 
-	if (mpi->mdev_events.notifier_call)
-		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
-	mpi->mdev_events.notifier_call = NULL;
-
 	mpi->ibdev = NULL;
 
 	spin_unlock(&port->mp.mpi_lock);
+	if (mpi->mdev_events.notifier_call)
+		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
+	mpi->mdev_events.notifier_call = NULL;
 	mlx5_remove_netdev_notifier(ibdev, port_num);
 	spin_lock(&port->mp.mpi_lock);
 
-- 
2.20.1

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Doug Ledford]

[-- Attachment #1: Type: text/plain, Size: 6111 bytes --]

On Wed, 2019-07-31 at 11:38 +0300, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@mellanox.com>
> 
> The below kernel panic was observed when created bond mode LACP
> with GRE tunnel on top. The reason to it was not released spinlock
> during mlx5 notify unregsiter sequence.
> 
> [  234.562007] BUG: scheduling while atomic: sh/10900/0x00000002
> [  234.563005] Preemption disabled at:
> [  234.566864] ------------[ cut here ]------------
> [  234.567120] DEBUG_LOCKS_WARN_ON(val > preempt_count())
> [  234.567139] WARNING: CPU: 16 PID: 10900 at kernel/sched/core.c:3203
> preempt_count_sub+0xca/0x170
> [  234.569550] CPU: 16 PID: 10900 Comm: sh Tainted: G        W 5.2.0-
> rc1-for-linust-dbg-2019-05-25_04-57-33-60 #1
> [  234.569886] Hardware name: Dell Inc. PowerEdge R720/0X3D66, BIOS
> 2.6.1 02/12/2018
> [  234.570183] RIP: 0010:preempt_count_sub+0xca/0x170
> [  234.570404] Code: 03 38
> d0 7c 08 84 d2 0f 85 b0 00 00 00 8b 15 dd 02 03 04 85 d2 75 ba 48 c7
> c6
> 00 e1 88 83 48 c7 c7 40 e1 88 83 e8 76 11 f7 ff <0f> 0b 5b c3 65 8b 05
> d3 1f d8 7e 84 c0 75 82 e8 62 c3 c3 00 85 c0
> [  234.570911] RSP: 0018:ffff888b94477b08 EFLAGS: 00010286
> [  234.571133] RAX: 0000000000000000 RBX: 0000000000000001 RCX:
> 0000000000000000
> [  234.571391] RDX: 0000000000000000 RSI: 0000000000000004 RDI:
> 0000000000000246
> [  234.571648] RBP: ffff888ba5560000 R08: fffffbfff08962d5 R09:
> fffffbfff08962d5
> [  234.571902] R10: 0000000000000001 R11: fffffbfff08962d4 R12:
> ffff888bac6e9548
> [  234.572157] R13: ffff888babfaf728 R14: ffff888bac6e9568 R15:
> ffff888babfaf750
> [  234.572412] FS: 00007fcafa59b740(0000) GS:ffff888bed200000(0000)
> knlGS:0000000000000000
> [  234.572686] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  234.572914] CR2: 00007f984f16b140 CR3: 0000000b2bf0a001 CR4:
> 00000000001606e0
> [  234.573172] Call Trace:
> [  234.573336] _raw_spin_unlock+0x2e/0x50
> [  234.573542] mlx5_ib_unbind_slave_port+0x1bc/0x690 [mlx5_ib]
> [  234.573793] mlx5_ib_cleanup_multiport_master+0x1d3/0x660 [mlx5_ib]
> [  234.574039] mlx5_ib_stage_init_cleanup+0x4c/0x360 [mlx5_ib]
> [  234.574271]  ? kfree+0xf5/0x2f0
> [  234.574465] __mlx5_ib_remove+0x61/0xd0 [mlx5_ib]
> [  234.574688]  ? __mlx5_ib_remove+0xd0/0xd0 [mlx5_ib]
> [  234.574951] mlx5_remove_device+0x234/0x300 [mlx5_core]
> [  234.575224] mlx5_unregister_device+0x4d/0x1e0 [mlx5_core]
> [  234.575493] remove_one+0x4f/0x160 [mlx5_core]
> [  234.575704] pci_device_remove+0xef/0x2a0
> [  234.581407]  ? pcibios_free_irq+0x10/0x10
> [  234.587143]  ? up_read+0xc1/0x260
> [  234.592785] device_release_driver_internal+0x1ab/0x430
> [  234.598442] unbind_store+0x152/0x200
> [  234.604064]  ? sysfs_kf_write+0x3b/0x180
> [  234.609441]  ? sysfs_file_ops+0x160/0x160
> [  234.615021] kernfs_fop_write+0x277/0x440
> [  234.620288]  ? __sb_start_write+0x1ef/0x2c0
> [  234.625512] vfs_write+0x15e/0x460
> [  234.630786] ksys_write+0x156/0x1e0
> [  234.635988]  ? __ia32_sys_read+0xb0/0xb0
> [  234.641120]  ? trace_hardirqs_off_thunk+0x1a/0x1c
> [  234.646163] do_syscall_64+0x95/0x470
> [  234.651106] entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [  234.656004] RIP: 0033:0x7fcaf9c9cfd0
> [  234.660686] Code: 73 01
> c3 48 8b 0d c0 6e 2d 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00
> 00
> 83 3d cd cf 2d 00 00 75 10 b8 01 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73
> 31 c3 48 83 ec 08 e8 ee cb 01 00 48 89 04 24
> [  234.670128] RSP: 002b:00007ffd3b01ddd8 EFLAGS: 00000246 ORIG_RAX:
> 0000000000000001
> [  234.674811] RAX: ffffffffffffffda RBX: 000000000000000d RCX:
> 00007fcaf9c9cfd0
> [  234.679387] RDX: 000000000000000d RSI: 00007fcafa5c1000 RDI:
> 0000000000000001
> [  234.683848] RBP: 00007fcafa5c1000 R08: 000000000000000a R09:
> 00007fcafa59b740
> [  234.688167] R10: 00007ffd3b01d8e0 R11: 0000000000000246 R12:
> 00007fcaf9f75400
> [  234.692386] R13: 000000000000000d R14: 0000000000000001 R15:
> 0000000000000000
> [  234.696495] irq event stamp: 153067
> [  234.700525] hardirqs last enabled at (153067): [<ffffffff83258c39>]
> _raw_spin_unlock_irqrestore+0x59/0x70
> [  234.704665] hardirqs last disabled at (153066):
> [<ffffffff83259382>] _raw_spin_lock_irqsave+0x22/0x90
> [  234.708722] softirqs last enabled at (153058): [<ffffffff836006c5>]
> __do_softirq+0x6c5/0xb4e
> [  234.712673] softirqs last disabled at (153051):
> [<ffffffff81227c1d>] irq_exit+0x17d/0x1d0
> [  234.716601] ---[ end trace 5dbf096843ee9ce6 ]---
> 
> Fixes: df097a278c75 ("IB/mlx5: Use the new mlx5 core notifier API")
> Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
> ---
>  drivers/infiniband/hw/mlx5/main.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/infiniband/hw/mlx5/main.c
> b/drivers/infiniband/hw/mlx5/main.c
> index c2a5780cb394..e12a4404096b 100644
> --- a/drivers/infiniband/hw/mlx5/main.c
> +++ b/drivers/infiniband/hw/mlx5/main.c
> @@ -5802,13 +5802,12 @@ static void mlx5_ib_unbind_slave_port(struct
> mlx5_ib_dev *ibdev,
>  		return;
>  	}
>  
> -	if (mpi->mdev_events.notifier_call)
> -		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> -	mpi->mdev_events.notifier_call = NULL;
> -
>  	mpi->ibdev = NULL;
>  
>  	spin_unlock(&port->mp.mpi_lock);
> +	if (mpi->mdev_events.notifier_call)
> +		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> +	mpi->mdev_events.notifier_call = NULL;

I can see where this fixes the problem at hand, but this gives the
appearance of creating a new race.  Doing a check/unregister/set-null
series outside of any locks is a red flag to someone investigating the
code.  You should at least make note of the fact that calling unregister
more than once is safe.  If you're fine with it, I can add a comment and
take the patch, or you can resubmit.

>  	mlx5_remove_netdev_notifier(ibdev, port_num);
>  	spin_lock(&port->mp.mpi_lock);
>  

-- 
Doug Ledford <dledford@redhat.com>
    GPG KeyID: B826A3330E572FDD
    Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Jason Gunthorpe]

On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford wrote:
> > diff --git a/drivers/infiniband/hw/mlx5/main.c
> > b/drivers/infiniband/hw/mlx5/main.c
> > index c2a5780cb394..e12a4404096b 100644
> > +++ b/drivers/infiniband/hw/mlx5/main.c
> > @@ -5802,13 +5802,12 @@ static void mlx5_ib_unbind_slave_port(struct
> > mlx5_ib_dev *ibdev,
> >  		return;
> >  	}
> >  
> > -	if (mpi->mdev_events.notifier_call)
> > -		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > -	mpi->mdev_events.notifier_call = NULL;
> > -
> >  	mpi->ibdev = NULL;
> >  
> >  	spin_unlock(&port->mp.mpi_lock);
> > +	if (mpi->mdev_events.notifier_call)
> > +		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > +	mpi->mdev_events.notifier_call = NULL;
> 
> I can see where this fixes the problem at hand, but this gives the
> appearance of creating a new race.  Doing a check/unregister/set-null
> series outside of any locks is a red flag to someone investigating the
> code.  You should at least make note of the fact that calling unregister
> more than once is safe.  If you're fine with it, I can add a comment and
> take the patch, or you can resubmit.

Mucking about notifier_call like that is gross anyhow, maybe better to
delete it entirely.

Jason

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Leon Romanovsky]

On Wed, Jul 31, 2019 at 05:00:59PM +0000, Jason Gunthorpe wrote:
> On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford wrote:
> > > diff --git a/drivers/infiniband/hw/mlx5/main.c
> > > b/drivers/infiniband/hw/mlx5/main.c
> > > index c2a5780cb394..e12a4404096b 100644
> > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > @@ -5802,13 +5802,12 @@ static void mlx5_ib_unbind_slave_port(struct
> > > mlx5_ib_dev *ibdev,
> > >  		return;
> > >  	}
> > >
> > > -	if (mpi->mdev_events.notifier_call)
> > > -		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > -	mpi->mdev_events.notifier_call = NULL;
> > > -
> > >  	mpi->ibdev = NULL;
> > >
> > >  	spin_unlock(&port->mp.mpi_lock);
> > > +	if (mpi->mdev_events.notifier_call)
> > > +		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > +	mpi->mdev_events.notifier_call = NULL;
> >
> > I can see where this fixes the problem at hand, but this gives the
> > appearance of creating a new race.  Doing a check/unregister/set-null
> > series outside of any locks is a red flag to someone investigating the
> > code.  You should at least make note of the fact that calling unregister
> > more than once is safe.  If you're fine with it, I can add a comment and
> > take the patch, or you can resubmit.
>
> Mucking about notifier_call like that is gross anyhow, maybe better to
> delete it entirely.

What do you propose to delete?

Doug,

I wasn't excited about that code either, but decided to do less possible harm here.

Thanks

>
> Jason

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Jason Gunthorpe]

On Wed, Jul 31, 2019 at 08:09:44PM +0300, Leon Romanovsky wrote:
> On Wed, Jul 31, 2019 at 05:00:59PM +0000, Jason Gunthorpe wrote:
> > On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford wrote:
> > > > diff --git a/drivers/infiniband/hw/mlx5/main.c
> > > > b/drivers/infiniband/hw/mlx5/main.c
> > > > index c2a5780cb394..e12a4404096b 100644
> > > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > > @@ -5802,13 +5802,12 @@ static void mlx5_ib_unbind_slave_port(struct
> > > > mlx5_ib_dev *ibdev,
> > > >  		return;
> > > >  	}
> > > >
> > > > -	if (mpi->mdev_events.notifier_call)
> > > > -		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > > -	mpi->mdev_events.notifier_call = NULL;
> > > > -
> > > >  	mpi->ibdev = NULL;
> > > >
> > > >  	spin_unlock(&port->mp.mpi_lock);
> > > > +	if (mpi->mdev_events.notifier_call)
> > > > +		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > > +	mpi->mdev_events.notifier_call = NULL;
> > >
> > > I can see where this fixes the problem at hand, but this gives the
> > > appearance of creating a new race.  Doing a check/unregister/set-null
> > > series outside of any locks is a red flag to someone investigating the
> > > code.  You should at least make note of the fact that calling unregister
> > > more than once is safe.  If you're fine with it, I can add a comment and
> > > take the patch, or you can resubmit.
> >
> > Mucking about notifier_call like that is gross anyhow, maybe better to
> > delete it entirely.
> 
> What do you propose to delete?

The 'mpi->mdev_events.notifier_call = NULL;' and 'if
(mpi->mdev_events.notifier_call)'

Once it leaves the lock it stops doing anything useful.

If you need it, then we can't drop the lock, if you don't, it is just
dead code, delete it.

Jason

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Leon Romanovsky]

On Wed, Jul 31, 2019 at 05:22:19PM +0000, Jason Gunthorpe wrote:
> On Wed, Jul 31, 2019 at 08:09:44PM +0300, Leon Romanovsky wrote:
> > On Wed, Jul 31, 2019 at 05:00:59PM +0000, Jason Gunthorpe wrote:
> > > On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford wrote:
> > > > > diff --git a/drivers/infiniband/hw/mlx5/main.c
> > > > > b/drivers/infiniband/hw/mlx5/main.c
> > > > > index c2a5780cb394..e12a4404096b 100644
> > > > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > > > @@ -5802,13 +5802,12 @@ static void mlx5_ib_unbind_slave_port(struct
> > > > > mlx5_ib_dev *ibdev,
> > > > >  		return;
> > > > >  	}
> > > > >
> > > > > -	if (mpi->mdev_events.notifier_call)
> > > > > -		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > > > -	mpi->mdev_events.notifier_call = NULL;
> > > > > -
> > > > >  	mpi->ibdev = NULL;
> > > > >
> > > > >  	spin_unlock(&port->mp.mpi_lock);
> > > > > +	if (mpi->mdev_events.notifier_call)
> > > > > +		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > > > +	mpi->mdev_events.notifier_call = NULL;
> > > >
> > > > I can see where this fixes the problem at hand, but this gives the
> > > > appearance of creating a new race.  Doing a check/unregister/set-null
> > > > series outside of any locks is a red flag to someone investigating the
> > > > code.  You should at least make note of the fact that calling unregister
> > > > more than once is safe.  If you're fine with it, I can add a comment and
> > > > take the patch, or you can resubmit.
> > >
> > > Mucking about notifier_call like that is gross anyhow, maybe better to
> > > delete it entirely.
> >
> > What do you propose to delete?
>
> The 'mpi->mdev_events.notifier_call = NULL;' and 'if
> (mpi->mdev_events.notifier_call)'
>
> Once it leaves the lock it stops doing anything useful.
>
> If you need it, then we can't drop the lock, if you don't, it is just
> dead code, delete it.

This specific notifier_call is protected outside
of mlx5_ib_unbind_slave_port() by mlx5_ib_multiport_mutex and NULL check
is needed to ensure single call to mlx5_notifier_unregister, because
calls to mlx5_ib_unbind_slave_port() will be serialized.

Thanks

>
> Jason

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Doug Ledford]

[-- Attachment #1: Type: text/plain, Size: 2799 bytes --]

On Wed, 2019-07-31 at 21:01 +0300, Leon Romanovsky wrote:
> On Wed, Jul 31, 2019 at 05:22:19PM +0000, Jason Gunthorpe wrote:
> > On Wed, Jul 31, 2019 at 08:09:44PM +0300, Leon Romanovsky wrote:
> > > On Wed, Jul 31, 2019 at 05:00:59PM +0000, Jason Gunthorpe wrote:
> > > > On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford wrote:
> > > > > > diff --git a/drivers/infiniband/hw/mlx5/main.c
> > > > > > b/drivers/infiniband/hw/mlx5/main.c
> > > > > > index c2a5780cb394..e12a4404096b 100644
> > > > > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > > > > @@ -5802,13 +5802,12 @@ static void
> > > > > > mlx5_ib_unbind_slave_port(struct
> > > > > > mlx5_ib_dev *ibdev,
> > > > > >  		return;
> > > > > >  	}
> > > > > > 
> > > > > > -	if (mpi->mdev_events.notifier_call)
> > > > > > -		mlx5_notifier_unregister(mpi->mdev, &mpi-
> > > > > > >mdev_events);
> > > > > > -	mpi->mdev_events.notifier_call = NULL;
> > > > > > -
> > > > > >  	mpi->ibdev = NULL;
> > > > > > 
> > > > > >  	spin_unlock(&port->mp.mpi_lock);
> > > > > > +	if (mpi->mdev_events.notifier_call)
> > > > > > +		mlx5_notifier_unregister(mpi->mdev, &mpi-
> > > > > > >mdev_events);
> > > > > > +	mpi->mdev_events.notifier_call = NULL;
> > > > > 
> > > > > I can see where this fixes the problem at hand, but this gives
> > > > > the
> > > > > appearance of creating a new race.  Doing a
> > > > > check/unregister/set-null
> > > > > series outside of any locks is a red flag to someone
> > > > > investigating the
> > > > > code.  You should at least make note of the fact that calling
> > > > > unregister
> > > > > more than once is safe.  If you're fine with it, I can add a
> > > > > comment and
> > > > > take the patch, or you can resubmit.
> > > > 
> > > > Mucking about notifier_call like that is gross anyhow, maybe
> > > > better to
> > > > delete it entirely.
> > > 
> > > What do you propose to delete?
> > 
> > The 'mpi->mdev_events.notifier_call = NULL;' and 'if
> > (mpi->mdev_events.notifier_call)'
> > 
> > Once it leaves the lock it stops doing anything useful.
> > 
> > If you need it, then we can't drop the lock, if you don't, it is
> > just
> > dead code, delete it.
> 
> This specific notifier_call is protected outside
> of mlx5_ib_unbind_slave_port() by mlx5_ib_multiport_mutex and NULL
> check
> is needed to ensure single call to mlx5_notifier_unregister, because
> calls to mlx5_ib_unbind_slave_port() will be serialized.

But looking at the code, it doesn't appear mlx5_notifier_unregister
requires there to only be a single call.  It's safe to call it multiple
times for the same notifier.

-- 
Doug Ledford <dledford@redhat.com>
    GPG KeyID: B826A3330E572FDD
    Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Jason Gunthorpe]

On Wed, Jul 31, 2019 at 09:01:24PM +0300, Leon Romanovsky wrote:
> On Wed, Jul 31, 2019 at 05:22:19PM +0000, Jason Gunthorpe wrote:
> > On Wed, Jul 31, 2019 at 08:09:44PM +0300, Leon Romanovsky wrote:
> > > On Wed, Jul 31, 2019 at 05:00:59PM +0000, Jason Gunthorpe wrote:
> > > > On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford wrote:
> > > > > > diff --git a/drivers/infiniband/hw/mlx5/main.c
> > > > > > b/drivers/infiniband/hw/mlx5/main.c
> > > > > > index c2a5780cb394..e12a4404096b 100644
> > > > > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > > > > @@ -5802,13 +5802,12 @@ static void mlx5_ib_unbind_slave_port(struct
> > > > > > mlx5_ib_dev *ibdev,
> > > > > >  		return;
> > > > > >  	}
> > > > > >
> > > > > > -	if (mpi->mdev_events.notifier_call)
> > > > > > -		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > > > > -	mpi->mdev_events.notifier_call = NULL;
> > > > > > -
> > > > > >  	mpi->ibdev = NULL;
> > > > > >
> > > > > >  	spin_unlock(&port->mp.mpi_lock);
> > > > > > +	if (mpi->mdev_events.notifier_call)
> > > > > > +		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > > > > +	mpi->mdev_events.notifier_call = NULL;
> > > > >
> > > > > I can see where this fixes the problem at hand, but this gives the
> > > > > appearance of creating a new race.  Doing a check/unregister/set-null
> > > > > series outside of any locks is a red flag to someone investigating the
> > > > > code.  You should at least make note of the fact that calling unregister
> > > > > more than once is safe.  If you're fine with it, I can add a comment and
> > > > > take the patch, or you can resubmit.
> > > >
> > > > Mucking about notifier_call like that is gross anyhow, maybe better to
> > > > delete it entirely.
> > >
> > > What do you propose to delete?
> >
> > The 'mpi->mdev_events.notifier_call = NULL;' and 'if
> > (mpi->mdev_events.notifier_call)'
> >
> > Once it leaves the lock it stops doing anything useful.
> >
> > If you need it, then we can't drop the lock, if you don't, it is just
> > dead code, delete it.
> 
> This specific notifier_call is protected outside
> of mlx5_ib_unbind_slave_port() by mlx5_ib_multiport_mutex and NULL check
> is needed to ensure single call to mlx5_notifier_unregister, because
> calls to mlx5_ib_unbind_slave_port() will be serialized.

If this routine is now relying on locking that is not obvious in the
function itself then add a lockdep too.

Jason

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Leon Romanovsky]

On Wed, Jul 31, 2019 at 02:51:42PM -0400, Doug Ledford wrote:
> On Wed, 2019-07-31 at 21:01 +0300, Leon Romanovsky wrote:
> > On Wed, Jul 31, 2019 at 05:22:19PM +0000, Jason Gunthorpe wrote:
> > > On Wed, Jul 31, 2019 at 08:09:44PM +0300, Leon Romanovsky wrote:
> > > > On Wed, Jul 31, 2019 at 05:00:59PM +0000, Jason Gunthorpe wrote:
> > > > > On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford wrote:
> > > > > > > diff --git a/drivers/infiniband/hw/mlx5/main.c
> > > > > > > b/drivers/infiniband/hw/mlx5/main.c
> > > > > > > index c2a5780cb394..e12a4404096b 100644
> > > > > > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > > > > > @@ -5802,13 +5802,12 @@ static void
> > > > > > > mlx5_ib_unbind_slave_port(struct
> > > > > > > mlx5_ib_dev *ibdev,
> > > > > > >  		return;
> > > > > > >  	}
> > > > > > >
> > > > > > > -	if (mpi->mdev_events.notifier_call)
> > > > > > > -		mlx5_notifier_unregister(mpi->mdev, &mpi-
> > > > > > > >mdev_events);
> > > > > > > -	mpi->mdev_events.notifier_call = NULL;
> > > > > > > -
> > > > > > >  	mpi->ibdev = NULL;
> > > > > > >
> > > > > > >  	spin_unlock(&port->mp.mpi_lock);
> > > > > > > +	if (mpi->mdev_events.notifier_call)
> > > > > > > +		mlx5_notifier_unregister(mpi->mdev, &mpi-
> > > > > > > >mdev_events);
> > > > > > > +	mpi->mdev_events.notifier_call = NULL;
> > > > > >
> > > > > > I can see where this fixes the problem at hand, but this gives
> > > > > > the
> > > > > > appearance of creating a new race.  Doing a
> > > > > > check/unregister/set-null
> > > > > > series outside of any locks is a red flag to someone
> > > > > > investigating the
> > > > > > code.  You should at least make note of the fact that calling
> > > > > > unregister
> > > > > > more than once is safe.  If you're fine with it, I can add a
> > > > > > comment and
> > > > > > take the patch, or you can resubmit.
> > > > >
> > > > > Mucking about notifier_call like that is gross anyhow, maybe
> > > > > better to
> > > > > delete it entirely.
> > > >
> > > > What do you propose to delete?
> > >
> > > The 'mpi->mdev_events.notifier_call = NULL;' and 'if
> > > (mpi->mdev_events.notifier_call)'
> > >
> > > Once it leaves the lock it stops doing anything useful.
> > >
> > > If you need it, then we can't drop the lock, if you don't, it is
> > > just
> > > dead code, delete it.
> >
> > This specific notifier_call is protected outside
> > of mlx5_ib_unbind_slave_port() by mlx5_ib_multiport_mutex and NULL
> > check
> > is needed to ensure single call to mlx5_notifier_unregister, because
> > calls to mlx5_ib_unbind_slave_port() will be serialized.
>
> But looking at the code, it doesn't appear mlx5_notifier_unregister
> requires there to only be a single call.  It's safe to call it multiple
> times for the same notifier.

I think so.

>
> --
> Doug Ledford <dledford@redhat.com>
>     GPG KeyID: B826A3330E572FDD
>     Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Leon Romanovsky]

On Wed, Jul 31, 2019 at 07:55:28PM +0000, Jason Gunthorpe wrote:
> On Wed, Jul 31, 2019 at 09:01:24PM +0300, Leon Romanovsky wrote:
> > On Wed, Jul 31, 2019 at 05:22:19PM +0000, Jason Gunthorpe wrote:
> > > On Wed, Jul 31, 2019 at 08:09:44PM +0300, Leon Romanovsky wrote:
> > > > On Wed, Jul 31, 2019 at 05:00:59PM +0000, Jason Gunthorpe wrote:
> > > > > On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford wrote:
> > > > > > > diff --git a/drivers/infiniband/hw/mlx5/main.c
> > > > > > > b/drivers/infiniband/hw/mlx5/main.c
> > > > > > > index c2a5780cb394..e12a4404096b 100644
> > > > > > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > > > > > @@ -5802,13 +5802,12 @@ static void mlx5_ib_unbind_slave_port(struct
> > > > > > > mlx5_ib_dev *ibdev,
> > > > > > >  		return;
> > > > > > >  	}
> > > > > > >
> > > > > > > -	if (mpi->mdev_events.notifier_call)
> > > > > > > -		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > > > > > -	mpi->mdev_events.notifier_call = NULL;
> > > > > > > -
> > > > > > >  	mpi->ibdev = NULL;
> > > > > > >
> > > > > > >  	spin_unlock(&port->mp.mpi_lock);
> > > > > > > +	if (mpi->mdev_events.notifier_call)
> > > > > > > +		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > > > > > +	mpi->mdev_events.notifier_call = NULL;
> > > > > >
> > > > > > I can see where this fixes the problem at hand, but this gives the
> > > > > > appearance of creating a new race.  Doing a check/unregister/set-null
> > > > > > series outside of any locks is a red flag to someone investigating the
> > > > > > code.  You should at least make note of the fact that calling unregister
> > > > > > more than once is safe.  If you're fine with it, I can add a comment and
> > > > > > take the patch, or you can resubmit.
> > > > >
> > > > > Mucking about notifier_call like that is gross anyhow, maybe better to
> > > > > delete it entirely.
> > > >
> > > > What do you propose to delete?
> > >
> > > The 'mpi->mdev_events.notifier_call = NULL;' and 'if
> > > (mpi->mdev_events.notifier_call)'
> > >
> > > Once it leaves the lock it stops doing anything useful.
> > >
> > > If you need it, then we can't drop the lock, if you don't, it is just
> > > dead code, delete it.
> >
> > This specific notifier_call is protected outside
> > of mlx5_ib_unbind_slave_port() by mlx5_ib_multiport_mutex and NULL check
> > is needed to ensure single call to mlx5_notifier_unregister, because
> > calls to mlx5_ib_unbind_slave_port() will be serialized.
>
> If this routine is now relying on locking that is not obvious in the
> function itself then add a lockdep too.

It was "before" without lockdep and we are
protecting "mpi->mdev_events.notifier_call = NULL;"

So why should we change this patch?

Thanks

>
> Jason

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Jason Gunthorpe]

On Thu, Aug 01, 2019 at 11:27:49AM +0300, Leon Romanovsky wrote:
> On Wed, Jul 31, 2019 at 07:55:28PM +0000, Jason Gunthorpe wrote:
> > On Wed, Jul 31, 2019 at 09:01:24PM +0300, Leon Romanovsky wrote:
> > > On Wed, Jul 31, 2019 at 05:22:19PM +0000, Jason Gunthorpe wrote:
> > > > On Wed, Jul 31, 2019 at 08:09:44PM +0300, Leon Romanovsky wrote:
> > > > > On Wed, Jul 31, 2019 at 05:00:59PM +0000, Jason Gunthorpe wrote:
> > > > > > On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford wrote:
> > > > > > > > diff --git a/drivers/infiniband/hw/mlx5/main.c
> > > > > > > > b/drivers/infiniband/hw/mlx5/main.c
> > > > > > > > index c2a5780cb394..e12a4404096b 100644
> > > > > > > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > > > > > > @@ -5802,13 +5802,12 @@ static void mlx5_ib_unbind_slave_port(struct
> > > > > > > > mlx5_ib_dev *ibdev,
> > > > > > > >  		return;
> > > > > > > >  	}
> > > > > > > >
> > > > > > > > -	if (mpi->mdev_events.notifier_call)
> > > > > > > > -		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > > > > > > -	mpi->mdev_events.notifier_call = NULL;
> > > > > > > > -
> > > > > > > >  	mpi->ibdev = NULL;
> > > > > > > >
> > > > > > > >  	spin_unlock(&port->mp.mpi_lock);
> > > > > > > > +	if (mpi->mdev_events.notifier_call)
> > > > > > > > +		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > > > > > > +	mpi->mdev_events.notifier_call = NULL;
> > > > > > >
> > > > > > > I can see where this fixes the problem at hand, but this gives the
> > > > > > > appearance of creating a new race.  Doing a check/unregister/set-null
> > > > > > > series outside of any locks is a red flag to someone investigating the
> > > > > > > code.  You should at least make note of the fact that calling unregister
> > > > > > > more than once is safe.  If you're fine with it, I can add a comment and
> > > > > > > take the patch, or you can resubmit.
> > > > > >
> > > > > > Mucking about notifier_call like that is gross anyhow, maybe better to
> > > > > > delete it entirely.
> > > > >
> > > > > What do you propose to delete?
> > > >
> > > > The 'mpi->mdev_events.notifier_call = NULL;' and 'if
> > > > (mpi->mdev_events.notifier_call)'
> > > >
> > > > Once it leaves the lock it stops doing anything useful.
> > > >
> > > > If you need it, then we can't drop the lock, if you don't, it is just
> > > > dead code, delete it.
> > >
> > > This specific notifier_call is protected outside
> > > of mlx5_ib_unbind_slave_port() by mlx5_ib_multiport_mutex and NULL check
> > > is needed to ensure single call to mlx5_notifier_unregister, because
> > > calls to mlx5_ib_unbind_slave_port() will be serialized.
> >
> > If this routine is now relying on locking that is not obvious in the
> > function itself then add a lockdep too.
> 
> It was "before" without lockdep and we are
> protecting "mpi->mdev_events.notifier_call = NULL;"

Before the locking was relying on mpi_lock inside this function now
this patch changes it to relies on mlx5_ib_multiport_mutex, so it
needs a lockdep

Jason

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Leon Romanovsky]

On Thu, Aug 01, 2019 at 12:00:12PM +0000, Jason Gunthorpe wrote:
> On Thu, Aug 01, 2019 at 11:27:49AM +0300, Leon Romanovsky wrote:
> > On Wed, Jul 31, 2019 at 07:55:28PM +0000, Jason Gunthorpe wrote:
> > > On Wed, Jul 31, 2019 at 09:01:24PM +0300, Leon Romanovsky wrote:
> > > > On Wed, Jul 31, 2019 at 05:22:19PM +0000, Jason Gunthorpe wrote:
> > > > > On Wed, Jul 31, 2019 at 08:09:44PM +0300, Leon Romanovsky wrote:
> > > > > > On Wed, Jul 31, 2019 at 05:00:59PM +0000, Jason Gunthorpe wrote:
> > > > > > > On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford wrote:
> > > > > > > > > diff --git a/drivers/infiniband/hw/mlx5/main.c
> > > > > > > > > b/drivers/infiniband/hw/mlx5/main.c
> > > > > > > > > index c2a5780cb394..e12a4404096b 100644
> > > > > > > > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > > > > > > > @@ -5802,13 +5802,12 @@ static void mlx5_ib_unbind_slave_port(struct
> > > > > > > > > mlx5_ib_dev *ibdev,
> > > > > > > > >  		return;
> > > > > > > > >  	}
> > > > > > > > >
> > > > > > > > > -	if (mpi->mdev_events.notifier_call)
> > > > > > > > > -		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > > > > > > > -	mpi->mdev_events.notifier_call = NULL;
> > > > > > > > > -
> > > > > > > > >  	mpi->ibdev = NULL;
> > > > > > > > >
> > > > > > > > >  	spin_unlock(&port->mp.mpi_lock);
> > > > > > > > > +	if (mpi->mdev_events.notifier_call)
> > > > > > > > > +		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > > > > > > > +	mpi->mdev_events.notifier_call = NULL;
> > > > > > > >
> > > > > > > > I can see where this fixes the problem at hand, but this gives the
> > > > > > > > appearance of creating a new race.  Doing a check/unregister/set-null
> > > > > > > > series outside of any locks is a red flag to someone investigating the
> > > > > > > > code.  You should at least make note of the fact that calling unregister
> > > > > > > > more than once is safe.  If you're fine with it, I can add a comment and
> > > > > > > > take the patch, or you can resubmit.
> > > > > > >
> > > > > > > Mucking about notifier_call like that is gross anyhow, maybe better to
> > > > > > > delete it entirely.
> > > > > >
> > > > > > What do you propose to delete?
> > > > >
> > > > > The 'mpi->mdev_events.notifier_call = NULL;' and 'if
> > > > > (mpi->mdev_events.notifier_call)'
> > > > >
> > > > > Once it leaves the lock it stops doing anything useful.
> > > > >
> > > > > If you need it, then we can't drop the lock, if you don't, it is just
> > > > > dead code, delete it.
> > > >
> > > > This specific notifier_call is protected outside
> > > > of mlx5_ib_unbind_slave_port() by mlx5_ib_multiport_mutex and NULL check
> > > > is needed to ensure single call to mlx5_notifier_unregister, because
> > > > calls to mlx5_ib_unbind_slave_port() will be serialized.
> > >
> > > If this routine is now relying on locking that is not obvious in the
> > > function itself then add a lockdep too.
> >
> > It was "before" without lockdep and we are
> > protecting "mpi->mdev_events.notifier_call = NULL;"
>
> Before the locking was relying on mpi_lock inside this function now
> this patch changes it to relies on mlx5_ib_multiport_mutex, so it
> needs a lockdep

It didn't rely, but was moved by mistake. I'll add lockdep and resend.

Thanks

>
> Jason

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Doug Ledford]

[-- Attachment #1: Type: text/plain, Size: 4794 bytes --]

On Thu, 2019-08-01 at 15:08 +0300, Leon Romanovsky wrote:
> On Thu, Aug 01, 2019 at 12:00:12PM +0000, Jason Gunthorpe wrote:
> > On Thu, Aug 01, 2019 at 11:27:49AM +0300, Leon Romanovsky wrote:
> > > On Wed, Jul 31, 2019 at 07:55:28PM +0000, Jason Gunthorpe wrote:
> > > > On Wed, Jul 31, 2019 at 09:01:24PM +0300, Leon Romanovsky wrote:
> > > > > On Wed, Jul 31, 2019 at 05:22:19PM +0000, Jason Gunthorpe
> > > > > wrote:
> > > > > > On Wed, Jul 31, 2019 at 08:09:44PM +0300, Leon Romanovsky
> > > > > > wrote:
> > > > > > > On Wed, Jul 31, 2019 at 05:00:59PM +0000, Jason Gunthorpe
> > > > > > > wrote:
> > > > > > > > On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford
> > > > > > > > wrote:
> > > > > > > > > > diff --git a/drivers/infiniband/hw/mlx5/main.c
> > > > > > > > > > b/drivers/infiniband/hw/mlx5/main.c
> > > > > > > > > > index c2a5780cb394..e12a4404096b 100644
> > > > > > > > > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > > > > > > > > @@ -5802,13 +5802,12 @@ static void
> > > > > > > > > > mlx5_ib_unbind_slave_port(struct
> > > > > > > > > > mlx5_ib_dev *ibdev,
> > > > > > > > > >  		return;
> > > > > > > > > >  	}
> > > > > > > > > > 
> > > > > > > > > > -	if (mpi->mdev_events.notifier_call)
> > > > > > > > > > -		mlx5_notifier_unregister(mpi->mdev,
> > > > > > > > > > &mpi->mdev_events);
> > > > > > > > > > -	mpi->mdev_events.notifier_call = NULL;
> > > > > > > > > > -
> > > > > > > > > >  	mpi->ibdev = NULL;
> > > > > > > > > > 
> > > > > > > > > >  	spin_unlock(&port->mp.mpi_lock);
> > > > > > > > > > +	if (mpi->mdev_events.notifier_call)
> > > > > > > > > > +		mlx5_notifier_unregister(mpi->mdev,
> > > > > > > > > > &mpi->mdev_events);
> > > > > > > > > > +	mpi->mdev_events.notifier_call = NULL;
> > > > > > > > > 
> > > > > > > > > I can see where this fixes the problem at hand, but
> > > > > > > > > this gives the
> > > > > > > > > appearance of creating a new race.  Doing a
> > > > > > > > > check/unregister/set-null
> > > > > > > > > series outside of any locks is a red flag to someone
> > > > > > > > > investigating the
> > > > > > > > > code.  You should at least make note of the fact that
> > > > > > > > > calling unregister
> > > > > > > > > more than once is safe.  If you're fine with it, I can
> > > > > > > > > add a comment and
> > > > > > > > > take the patch, or you can resubmit.
> > > > > > > > 
> > > > > > > > Mucking about notifier_call like that is gross anyhow,
> > > > > > > > maybe better to
> > > > > > > > delete it entirely.
> > > > > > > 
> > > > > > > What do you propose to delete?
> > > > > > 
> > > > > > The 'mpi->mdev_events.notifier_call = NULL;' and 'if
> > > > > > (mpi->mdev_events.notifier_call)'
> > > > > > 
> > > > > > Once it leaves the lock it stops doing anything useful.
> > > > > > 
> > > > > > If you need it, then we can't drop the lock, if you don't,
> > > > > > it is just
> > > > > > dead code, delete it.
> > > > > 
> > > > > This specific notifier_call is protected outside
> > > > > of mlx5_ib_unbind_slave_port() by mlx5_ib_multiport_mutex and
> > > > > NULL check
> > > > > is needed to ensure single call to mlx5_notifier_unregister,
> > > > > because
> > > > > calls to mlx5_ib_unbind_slave_port() will be serialized.
> > > > 
> > > > If this routine is now relying on locking that is not obvious in
> > > > the
> > > > function itself then add a lockdep too.
> > > 
> > > It was "before" without lockdep and we are
> > > protecting "mpi->mdev_events.notifier_call = NULL;"
> > 
> > Before the locking was relying on mpi_lock inside this function now
> > this patch changes it to relies on mlx5_ib_multiport_mutex, so it
> > needs a lockdep
> 
> It didn't rely, but was moved by mistake. I'll add lockdep and resend.
> 
> Thanks

There's no need for a lockdep.  The removal of the notifier callback
entry is re-entrant safe.  The core removal routines have their own
spinlock they use to protect the actual notifier list.  If you call it
more than once, the second and subsequent calls merely scan the list,
find no matching entry, and return ENOENT.  The only reason this might
need a lock and a lockdep entry is if you are protecting against a race
with the *add* notifier code in the mlx5 driver specifically (the core
add code won't have an issue, but since you only have a single place to
store the notifier callback pointer, if it would be possible for you to
add two callbacks and write over the first callback pointer with the
second without removing the first, then you would leak a callback
notifier in the core notifier list).

-- 
Doug Ledford <dledford@redhat.com>
    GPG KeyID: B826A3330E572FDD
    Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Leon Romanovsky]

On Thu, Aug 01, 2019 at 10:16:23AM -0400, Doug Ledford wrote:
> On Thu, 2019-08-01 at 15:08 +0300, Leon Romanovsky wrote:
> > On Thu, Aug 01, 2019 at 12:00:12PM +0000, Jason Gunthorpe wrote:
> > > On Thu, Aug 01, 2019 at 11:27:49AM +0300, Leon Romanovsky wrote:
> > > > On Wed, Jul 31, 2019 at 07:55:28PM +0000, Jason Gunthorpe wrote:
> > > > > On Wed, Jul 31, 2019 at 09:01:24PM +0300, Leon Romanovsky wrote:
> > > > > > On Wed, Jul 31, 2019 at 05:22:19PM +0000, Jason Gunthorpe
> > > > > > wrote:
> > > > > > > On Wed, Jul 31, 2019 at 08:09:44PM +0300, Leon Romanovsky
> > > > > > > wrote:
> > > > > > > > On Wed, Jul 31, 2019 at 05:00:59PM +0000, Jason Gunthorpe
> > > > > > > > wrote:
> > > > > > > > > On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford
> > > > > > > > > wrote:
> > > > > > > > > > > diff --git a/drivers/infiniband/hw/mlx5/main.c
> > > > > > > > > > > b/drivers/infiniband/hw/mlx5/main.c
> > > > > > > > > > > index c2a5780cb394..e12a4404096b 100644
> > > > > > > > > > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > > > > > > > > > @@ -5802,13 +5802,12 @@ static void
> > > > > > > > > > > mlx5_ib_unbind_slave_port(struct
> > > > > > > > > > > mlx5_ib_dev *ibdev,
> > > > > > > > > > >  		return;
> > > > > > > > > > >  	}
> > > > > > > > > > >
> > > > > > > > > > > -	if (mpi->mdev_events.notifier_call)
> > > > > > > > > > > -		mlx5_notifier_unregister(mpi->mdev,
> > > > > > > > > > > &mpi->mdev_events);
> > > > > > > > > > > -	mpi->mdev_events.notifier_call = NULL;
> > > > > > > > > > > -
> > > > > > > > > > >  	mpi->ibdev = NULL;
> > > > > > > > > > >
> > > > > > > > > > >  	spin_unlock(&port->mp.mpi_lock);
> > > > > > > > > > > +	if (mpi->mdev_events.notifier_call)
> > > > > > > > > > > +		mlx5_notifier_unregister(mpi->mdev,
> > > > > > > > > > > &mpi->mdev_events);
> > > > > > > > > > > +	mpi->mdev_events.notifier_call = NULL;
> > > > > > > > > >
> > > > > > > > > > I can see where this fixes the problem at hand, but
> > > > > > > > > > this gives the
> > > > > > > > > > appearance of creating a new race.  Doing a
> > > > > > > > > > check/unregister/set-null
> > > > > > > > > > series outside of any locks is a red flag to someone
> > > > > > > > > > investigating the
> > > > > > > > > > code.  You should at least make note of the fact that
> > > > > > > > > > calling unregister
> > > > > > > > > > more than once is safe.  If you're fine with it, I can
> > > > > > > > > > add a comment and
> > > > > > > > > > take the patch, or you can resubmit.
> > > > > > > > >
> > > > > > > > > Mucking about notifier_call like that is gross anyhow,
> > > > > > > > > maybe better to
> > > > > > > > > delete it entirely.
> > > > > > > >
> > > > > > > > What do you propose to delete?
> > > > > > >
> > > > > > > The 'mpi->mdev_events.notifier_call = NULL;' and 'if
> > > > > > > (mpi->mdev_events.notifier_call)'
> > > > > > >
> > > > > > > Once it leaves the lock it stops doing anything useful.
> > > > > > >
> > > > > > > If you need it, then we can't drop the lock, if you don't,
> > > > > > > it is just
> > > > > > > dead code, delete it.
> > > > > >
> > > > > > This specific notifier_call is protected outside
> > > > > > of mlx5_ib_unbind_slave_port() by mlx5_ib_multiport_mutex and
> > > > > > NULL check
> > > > > > is needed to ensure single call to mlx5_notifier_unregister,
> > > > > > because
> > > > > > calls to mlx5_ib_unbind_slave_port() will be serialized.
> > > > >
> > > > > If this routine is now relying on locking that is not obvious in
> > > > > the
> > > > > function itself then add a lockdep too.
> > > >
> > > > It was "before" without lockdep and we are
> > > > protecting "mpi->mdev_events.notifier_call = NULL;"
> > >
> > > Before the locking was relying on mpi_lock inside this function now
> > > this patch changes it to relies on mlx5_ib_multiport_mutex, so it
> > > needs a lockdep
> >
> > It didn't rely, but was moved by mistake. I'll add lockdep and resend.
> >
> > Thanks
>
> There's no need for a lockdep.  The removal of the notifier callback
> entry is re-entrant safe.  The core removal routines have their own
> spinlock they use to protect the actual notifier list.  If you call it
> more than once, the second and subsequent calls merely scan the list,
> find no matching entry, and return ENOENT.  The only reason this might
> need a lock and a lockdep entry is if you are protecting against a race
> with the *add* notifier code in the mlx5 driver specifically (the core
> add code won't have an issue, but since you only have a single place to
> store the notifier callback pointer, if it would be possible for you to
> add two callbacks and write over the first callback pointer with the
> second without removing the first, then you would leak a callback
> notifier in the core notifier list).

atomic_notifier_chain_unregister() unconditionally calls to
syncronize_rcu() and I'm not so sure that it is best thing to do
for every port unbind.

Actually, I'm completely lost here, we are all agree that the patch
fixes issue correctly, and it returns the code to be exactly as
it was before commit df097a278c75 ("IB/mlx5: Use the new mlx5 core notifier
API"). Can we simply merge it and fix the kernel panic?

Thanks

>
> --
> Doug Ledford <dledford@redhat.com>
>     GPG KeyID: B826A3330E572FDD
>     Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Doug Ledford]

[-- Attachment #1: Type: text/plain, Size: 2005 bytes --]

On Thu, 2019-08-01 at 18:59 +0300, Leon Romanovsky wrote:
> > There's no need for a lockdep.  The removal of the notifier callback
> > entry is re-entrant safe.  The core removal routines have their own
> > spinlock they use to protect the actual notifier list.  If you call
> > it
> > more than once, the second and subsequent calls merely scan the
> > list,
> > find no matching entry, and return ENOENT.  The only reason this
> > might
> > need a lock and a lockdep entry is if you are protecting against a
> > race
> > with the *add* notifier code in the mlx5 driver specifically (the
> > core
> > add code won't have an issue, but since you only have a single place
> > to
> > store the notifier callback pointer, if it would be possible for you
> > to
> > add two callbacks and write over the first callback pointer with the
> > second without removing the first, then you would leak a callback
> > notifier in the core notifier list).
> 
> atomic_notifier_chain_unregister() unconditionally calls to
> syncronize_rcu() and I'm not so sure that it is best thing to do
> for every port unbind.
> 
> Actually, I'm completely lost here, we are all agree that the patch
> fixes issue correctly, and it returns the code to be exactly as
> it was before commit df097a278c75 ("IB/mlx5: Use the new mlx5 core
> notifier
> API"). Can we simply merge it and fix the kernel panic?

As long as you are OK with me adding a comment to the patch so people
coming back later won't scratch their head about how can it possible be
right to do that sequence without a lock held, I'm fine merging the fix.

Something like:

/*
 * The check/unregister/set-NULL sequence below does not need to be
 * locked for correctness as it's only an optimization, and can't
 * be under a lock or will throw a scheduling while atomic error.
 */

-- 
Doug Ledford <dledford@redhat.com>
    GPG KeyID: B826A3330E572FDD
    Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Jason Gunthorpe]

On Thu, Aug 01, 2019 at 12:11:20PM -0400, Doug Ledford wrote:
> On Thu, 2019-08-01 at 18:59 +0300, Leon Romanovsky wrote:
> > > There's no need for a lockdep.  The removal of the notifier callback
> > > entry is re-entrant safe.  The core removal routines have their own
> > > spinlock they use to protect the actual notifier list.  If you call
> > > it
> > > more than once, the second and subsequent calls merely scan the
> > > list,
> > > find no matching entry, and return ENOENT.  The only reason this
> > > might
> > > need a lock and a lockdep entry is if you are protecting against a
> > > race
> > > with the *add* notifier code in the mlx5 driver specifically (the
> > > core
> > > add code won't have an issue, but since you only have a single place
> > > to
> > > store the notifier callback pointer, if it would be possible for you
> > > to
> > > add two callbacks and write over the first callback pointer with the
> > > second without removing the first, then you would leak a callback
> > > notifier in the core notifier list).
> > 
> > atomic_notifier_chain_unregister() unconditionally calls to
> > syncronize_rcu() and I'm not so sure that it is best thing to do
> > for every port unbind.
> > 
> > Actually, I'm completely lost here, we are all agree that the patch
> > fixes issue correctly, and it returns the code to be exactly as
> > it was before commit df097a278c75 ("IB/mlx5: Use the new mlx5 core
> > notifier
> > API"). Can we simply merge it and fix the kernel panic?
> 
> As long as you are OK with me adding a comment to the patch so people
> coming back later won't scratch their head about how can it possible be
> right to do that sequence without a lock held, I'm fine merging the fix.
> 
> Something like:
> 
> /*
>  * The check/unregister/set-NULL sequence below does not need to be
>  * locked for correctness as it's only an optimization, and can't
>  * be under a lock or will throw a scheduling while atomic error.
>  */

It does have a lock though, the caller holds it, hence the request for
the lockdep.

Jason

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Leon Romanovsky]

On Thu, Aug 01, 2019 at 12:11:20PM -0400, Doug Ledford wrote:
> On Thu, 2019-08-01 at 18:59 +0300, Leon Romanovsky wrote:
> > > There's no need for a lockdep.  The removal of the notifier callback
> > > entry is re-entrant safe.  The core removal routines have their own
> > > spinlock they use to protect the actual notifier list.  If you call
> > > it
> > > more than once, the second and subsequent calls merely scan the
> > > list,
> > > find no matching entry, and return ENOENT.  The only reason this
> > > might
> > > need a lock and a lockdep entry is if you are protecting against a
> > > race
> > > with the *add* notifier code in the mlx5 driver specifically (the
> > > core
> > > add code won't have an issue, but since you only have a single place
> > > to
> > > store the notifier callback pointer, if it would be possible for you
> > > to
> > > add two callbacks and write over the first callback pointer with the
> > > second without removing the first, then you would leak a callback
> > > notifier in the core notifier list).
> >
> > atomic_notifier_chain_unregister() unconditionally calls to
> > syncronize_rcu() and I'm not so sure that it is best thing to do
> > for every port unbind.
> >
> > Actually, I'm completely lost here, we are all agree that the patch
> > fixes issue correctly, and it returns the code to be exactly as
> > it was before commit df097a278c75 ("IB/mlx5: Use the new mlx5 core
> > notifier
> > API"). Can we simply merge it and fix the kernel panic?
>
> As long as you are OK with me adding a comment to the patch so people
> coming back later won't scratch their head about how can it possible be
> right to do that sequence without a lock held, I'm fine merging the fix.
>
> Something like:
>
> /*
>  * The check/unregister/set-NULL sequence below does not need to be
>  * locked for correctness as it's only an optimization, and can't
>  * be under a lock or will throw a scheduling while atomic error.
>  */

I think that the best place will be in commit message for this explanation,
but I'm fine with the comment inside code as well.

Thanks a lot, I appreciate it.

>
> --
> Doug Ledford <dledford@redhat.com>
>     GPG KeyID: B826A3330E572FDD
>     Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Doug Ledford]

[-- Attachment #1: Type: text/plain, Size: 2643 bytes --]

On Thu, 2019-08-01 at 16:20 +0000, Jason Gunthorpe wrote:
> On Thu, Aug 01, 2019 at 12:11:20PM -0400, Doug Ledford wrote:
> > On Thu, 2019-08-01 at 18:59 +0300, Leon Romanovsky wrote:
> > > > There's no need for a lockdep.  The removal of the notifier
> > > > callback
> > > > entry is re-entrant safe.  The core removal routines have their
> > > > own
> > > > spinlock they use to protect the actual notifier list.  If you
> > > > call
> > > > it
> > > > more than once, the second and subsequent calls merely scan the
> > > > list,
> > > > find no matching entry, and return ENOENT.  The only reason this
> > > > might
> > > > need a lock and a lockdep entry is if you are protecting against
> > > > a
> > > > race
> > > > with the *add* notifier code in the mlx5 driver specifically
> > > > (the
> > > > core
> > > > add code won't have an issue, but since you only have a single
> > > > place
> > > > to
> > > > store the notifier callback pointer, if it would be possible for
> > > > you
> > > > to
> > > > add two callbacks and write over the first callback pointer with
> > > > the
> > > > second without removing the first, then you would leak a
> > > > callback
> > > > notifier in the core notifier list).
> > > 
> > > atomic_notifier_chain_unregister() unconditionally calls to
> > > syncronize_rcu() and I'm not so sure that it is best thing to do
> > > for every port unbind.
> > > 
> > > Actually, I'm completely lost here, we are all agree that the
> > > patch
> > > fixes issue correctly, and it returns the code to be exactly as
> > > it was before commit df097a278c75 ("IB/mlx5: Use the new mlx5 core
> > > notifier
> > > API"). Can we simply merge it and fix the kernel panic?
> > 
> > As long as you are OK with me adding a comment to the patch so
> > people
> > coming back later won't scratch their head about how can it possible
> > be
> > right to do that sequence without a lock held, I'm fine merging the
> > fix.
> > 
> > Something like:
> > 
> > /*
> >  * The check/unregister/set-NULL sequence below does not need to be
> >  * locked for correctness as it's only an optimization, and can't
> >  * be under a lock or will throw a scheduling while atomic error.
> >  */
> 
> It does have a lock though, the caller holds it, hence the request for
> the lockdep.

You're right, although I think the lockdep annotation can be a separate
patch as it's neeeded on more than just the function this patch touches.

-- 
Doug Ledford <dledford@redhat.com>
    GPG KeyID: B826A3330E572FDD
    Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Doug Ledford]

[-- Attachment #1: Type: text/plain, Size: 2630 bytes --]

On Thu, 2019-08-01 at 19:23 +0300, Leon Romanovsky wrote:
> On Thu, Aug 01, 2019 at 12:11:20PM -0400, Doug Ledford wrote:
> > On Thu, 2019-08-01 at 18:59 +0300, Leon Romanovsky wrote:
> > > > There's no need for a lockdep.  The removal of the notifier
> > > > callback
> > > > entry is re-entrant safe.  The core removal routines have their
> > > > own
> > > > spinlock they use to protect the actual notifier list.  If you
> > > > call
> > > > it
> > > > more than once, the second and subsequent calls merely scan the
> > > > list,
> > > > find no matching entry, and return ENOENT.  The only reason this
> > > > might
> > > > need a lock and a lockdep entry is if you are protecting against
> > > > a
> > > > race
> > > > with the *add* notifier code in the mlx5 driver specifically
> > > > (the
> > > > core
> > > > add code won't have an issue, but since you only have a single
> > > > place
> > > > to
> > > > store the notifier callback pointer, if it would be possible for
> > > > you
> > > > to
> > > > add two callbacks and write over the first callback pointer with
> > > > the
> > > > second without removing the first, then you would leak a
> > > > callback
> > > > notifier in the core notifier list).
> > > 
> > > atomic_notifier_chain_unregister() unconditionally calls to
> > > syncronize_rcu() and I'm not so sure that it is best thing to do
> > > for every port unbind.
> > > 
> > > Actually, I'm completely lost here, we are all agree that the
> > > patch
> > > fixes issue correctly, and it returns the code to be exactly as
> > > it was before commit df097a278c75 ("IB/mlx5: Use the new mlx5 core
> > > notifier
> > > API"). Can we simply merge it and fix the kernel panic?
> > 
> > As long as you are OK with me adding a comment to the patch so
> > people
> > coming back later won't scratch their head about how can it possible
> > be
> > right to do that sequence without a lock held, I'm fine merging the
> > fix.
> > 
> > Something like:
> > 
> > /*
> >  * The check/unregister/set-NULL sequence below does not need to be
> >  * locked for correctness as it's only an optimization, and can't
> >  * be under a lock or will throw a scheduling while atomic error.
> >  */
> 
> I think that the best place will be in commit message for this
> explanation,
> but I'm fine with the comment inside code as well.
> 
> Thanks a lot, I appreciate it.

Patch (unmodified) is applied to for-rc, thanks.

-- 
Doug Ledford <dledford@redhat.com>
    GPG KeyID: B826A3330E572FDD
    Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Jason Gunthorpe]

On Thu, Aug 01, 2019 at 12:40:43PM -0400, Doug Ledford wrote:

> > It does have a lock though, the caller holds it, hence the request for
> > the lockdep.
> 
> You're right, although I think the lockdep annotation can be a separate
> patch as it's neeeded on more than just the function this patch touches.

Why? This relies on that lock, so it should have the
lockdep_assert_held assert.

If there are more functions with implicit locking theyt they can be
fixed separately...

Jason

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Doug Ledford]

[-- Attachment #1: Type: text/plain, Size: 1003 bytes --]

On Thu, 2019-08-01 at 16:43 +0000, Jason Gunthorpe wrote:
> On Thu, Aug 01, 2019 at 12:40:43PM -0400, Doug Ledford wrote:
> 
> > > It does have a lock though, the caller holds it, hence the request
> > > for
> > > the lockdep.
> > 
> > You're right, although I think the lockdep annotation can be a
> > separate
> > patch as it's neeeded on more than just the function this patch
> > touches.
> 
> Why? This relies on that lock, so it should have the
> lockdep_assert_held assert.

It does, but this patch is about the scheduling while atomic, adding a
lockdep assertion fix is doubling up on fixes in the patch.  A separate
patch that addes the lockdep assert to both the bind and unbind calls
makes more sense and just feels cleaner to me.

> If there are more functions with implicit locking theyt they can be
> fixed separately...

-- 
Doug Ledford <dledford@redhat.com>
    GPG KeyID: B826A3330E572FDD
    Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Leon Romanovsky]

On Thu, Aug 01, 2019 at 12:50:37PM -0400, Doug Ledford wrote:
> On Thu, 2019-08-01 at 16:43 +0000, Jason Gunthorpe wrote:
> > On Thu, Aug 01, 2019 at 12:40:43PM -0400, Doug Ledford wrote:
> >
> > > > It does have a lock though, the caller holds it, hence the request
> > > > for
> > > > the lockdep.
> > >
> > > You're right, although I think the lockdep annotation can be a
> > > separate
> > > patch as it's neeeded on more than just the function this patch
> > > touches.
> >
> > Why? This relies on that lock, so it should have the
> > lockdep_assert_held assert.
>
> It does, but this patch is about the scheduling while atomic, adding a
> lockdep assertion fix is doubling up on fixes in the patch.  A separate
> patch that addes the lockdep assert to both the bind and unbind calls
> makes more sense and just feels cleaner to me.

+1

Also, I'm not going to take any chances in -rc submission, and won't
change in -rc patches anything without verification approval and it will
take time and will come very late in -rcX.

Thanks

>
> > If there are more functions with implicit locking theyt they can be
> > fixed separately...
>
> --
> Doug Ledford <dledford@redhat.com>
>     GPG KeyID: B826A3330E572FDD
>     Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Leon Romanovsky]

On Thu, Aug 01, 2019 at 12:42:43PM -0400, Doug Ledford wrote:
> On Thu, 2019-08-01 at 19:23 +0300, Leon Romanovsky wrote:
> > On Thu, Aug 01, 2019 at 12:11:20PM -0400, Doug Ledford wrote:
> > > On Thu, 2019-08-01 at 18:59 +0300, Leon Romanovsky wrote:
> > > > > There's no need for a lockdep.  The removal of the notifier
> > > > > callback
> > > > > entry is re-entrant safe.  The core removal routines have their
> > > > > own
> > > > > spinlock they use to protect the actual notifier list.  If you
> > > > > call
> > > > > it
> > > > > more than once, the second and subsequent calls merely scan the
> > > > > list,
> > > > > find no matching entry, and return ENOENT.  The only reason this
> > > > > might
> > > > > need a lock and a lockdep entry is if you are protecting against
> > > > > a
> > > > > race
> > > > > with the *add* notifier code in the mlx5 driver specifically
> > > > > (the
> > > > > core
> > > > > add code won't have an issue, but since you only have a single
> > > > > place
> > > > > to
> > > > > store the notifier callback pointer, if it would be possible for
> > > > > you
> > > > > to
> > > > > add two callbacks and write over the first callback pointer with
> > > > > the
> > > > > second without removing the first, then you would leak a
> > > > > callback
> > > > > notifier in the core notifier list).
> > > >
> > > > atomic_notifier_chain_unregister() unconditionally calls to
> > > > syncronize_rcu() and I'm not so sure that it is best thing to do
> > > > for every port unbind.
> > > >
> > > > Actually, I'm completely lost here, we are all agree that the
> > > > patch
> > > > fixes issue correctly, and it returns the code to be exactly as
> > > > it was before commit df097a278c75 ("IB/mlx5: Use the new mlx5 core
> > > > notifier
> > > > API"). Can we simply merge it and fix the kernel panic?
> > >
> > > As long as you are OK with me adding a comment to the patch so
> > > people
> > > coming back later won't scratch their head about how can it possible
> > > be
> > > right to do that sequence without a lock held, I'm fine merging the
> > > fix.
> > >
> > > Something like:
> > >
> > > /*
> > >  * The check/unregister/set-NULL sequence below does not need to be
> > >  * locked for correctness as it's only an optimization, and can't
> > >  * be under a lock or will throw a scheduling while atomic error.
> > >  */
> >
> > I think that the best place will be in commit message for this
> > explanation,
> > but I'm fine with the comment inside code as well.
> >
> > Thanks a lot, I appreciate it.
>
> Patch (unmodified) is applied to for-rc, thanks.

Thanks Doug, I'll prepare patch with lockdep for Jason and
will submit it to -next later on after passing verification.

Thanks

>
> --
> Doug Ledford <dledford@redhat.com>
>     GPG KeyID: B826A3330E572FDD
>     Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Doug Ledford]

[-- Attachment #1: Type: text/plain, Size: 3351 bytes --]

On Thu, 2019-08-01 at 20:33 +0300, Leon Romanovsky wrote:
> On Thu, Aug 01, 2019 at 12:42:43PM -0400, Doug Ledford wrote:
> > On Thu, 2019-08-01 at 19:23 +0300, Leon Romanovsky wrote:
> > > On Thu, Aug 01, 2019 at 12:11:20PM -0400, Doug Ledford wrote:
> > > > On Thu, 2019-08-01 at 18:59 +0300, Leon Romanovsky wrote:
> > > > > > There's no need for a lockdep.  The removal of the notifier
> > > > > > callback
> > > > > > entry is re-entrant safe.  The core removal routines have
> > > > > > their
> > > > > > own
> > > > > > spinlock they use to protect the actual notifier list.  If
> > > > > > you
> > > > > > call
> > > > > > it
> > > > > > more than once, the second and subsequent calls merely scan
> > > > > > the
> > > > > > list,
> > > > > > find no matching entry, and return ENOENT.  The only reason
> > > > > > this
> > > > > > might
> > > > > > need a lock and a lockdep entry is if you are protecting
> > > > > > against
> > > > > > a
> > > > > > race
> > > > > > with the *add* notifier code in the mlx5 driver specifically
> > > > > > (the
> > > > > > core
> > > > > > add code won't have an issue, but since you only have a
> > > > > > single
> > > > > > place
> > > > > > to
> > > > > > store the notifier callback pointer, if it would be possible
> > > > > > for
> > > > > > you
> > > > > > to
> > > > > > add two callbacks and write over the first callback pointer
> > > > > > with
> > > > > > the
> > > > > > second without removing the first, then you would leak a
> > > > > > callback
> > > > > > notifier in the core notifier list).
> > > > > 
> > > > > atomic_notifier_chain_unregister() unconditionally calls to
> > > > > syncronize_rcu() and I'm not so sure that it is best thing to
> > > > > do
> > > > > for every port unbind.
> > > > > 
> > > > > Actually, I'm completely lost here, we are all agree that the
> > > > > patch
> > > > > fixes issue correctly, and it returns the code to be exactly
> > > > > as
> > > > > it was before commit df097a278c75 ("IB/mlx5: Use the new mlx5
> > > > > core
> > > > > notifier
> > > > > API"). Can we simply merge it and fix the kernel panic?
> > > > 
> > > > As long as you are OK with me adding a comment to the patch so
> > > > people
> > > > coming back later won't scratch their head about how can it
> > > > possible
> > > > be
> > > > right to do that sequence without a lock held, I'm fine merging
> > > > the
> > > > fix.
> > > > 
> > > > Something like:
> > > > 
> > > > /*
> > > >  * The check/unregister/set-NULL sequence below does not need to
> > > > be
> > > >  * locked for correctness as it's only an optimization, and
> > > > can't
> > > >  * be under a lock or will throw a scheduling while atomic
> > > > error.
> > > >  */
> > > 
> > > I think that the best place will be in commit message for this
> > > explanation,
> > > but I'm fine with the comment inside code as well.
> > > 
> > > Thanks a lot, I appreciate it.
> > 
> > Patch (unmodified) is applied to for-rc, thanks.
> 
> Thanks Doug, I'll prepare patch with lockdep for Jason and
> will submit it to -next later on after passing verification.

Perfect, thanks Leon.

-- 
Doug Ledford <dledford@redhat.com>
    GPG KeyID: B826A3330E572FDD
    Fingerprint = AE6B 1BDA 122B 23B4 265B  1274 B826 A333 0E57 2FDD

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