Re: [PATCH 1/2] IB/ipoib: Fix mcast list locking
From: Leon Romanovsky
Date: Mon Dec 11 2023 - 08:45:51 EST
On Mon, Dec 11, 2023 at 02:04:24PM +0100, Daniel Vacek wrote:
> We need an additional protection against list removal between ipoib_mcast_join_task()
> and ipoib_mcast_dev_flush() in case the &priv->lock needs to be dropped while
> iterating the &priv->multicast_list in ipoib_mcast_join_task(). If the mcast
> is removed while the lock was dropped, the for loop spins forever resulting
> in a hard lockup (as was reported on RHEL 4.18.0-372.75.1.el8_6 kernel):
>
> Task A (kworker/u72:2 below) | Task B (kworker/u72:0 below)
> -----------------------------------+-----------------------------------
> ipoib_mcast_join_task(work) | ipoib_ib_dev_flush_light(work)
> spin_lock_irq(&priv->lock) | __ipoib_ib_dev_flush(priv, ...)
> list_for_each_entry(mcast, | ipoib_mcast_dev_flush(dev = priv->dev)
> &priv->multicast_list, list) | mutex_lock(&priv->mcast_mutex)
> ipoib_mcast_join(dev, mcast) |
> spin_unlock_irq(&priv->lock) |
> | spin_lock_irqsave(&priv->lock, flags)
> | list_for_each_entry_safe(mcast, tmcast,
> | &priv->multicast_list, list)
> | list_del(&mcast->list);
> | list_add_tail(&mcast->list, &remove_list)
> | spin_unlock_irqrestore(&priv->lock, flags)
> spin_lock_irq(&priv->lock) |
> | ipoib_mcast_remove_list(&remove_list)
> (Here, mcast is no longer on the | list_for_each_entry_safe(mcast, tmcast,
> &priv->multicast_list and we keep | remove_list, list)
> spinning on the &remove_list of the \ >>> wait_for_completion(&mcast->done)
> other thread which is blocked and the|
> list is still valid on it's stack.) | mutex_unlock(&priv->mcast_mutex)
>
> Fix this by adding mutex_lock(&priv->mcast_mutex) to ipoib_mcast_join_task().
I don't entirely understand the issue and the proposed solution.
There is only one spin_unlock_irq() in the middle of list_for_each_entry(mcast, &priv->multicast_list, list)
and it is right before return statement which will break the loop. So
how will loop spin forever?
Thanks
> Unfortunately we could not reproduce the lockup and confirm this fix but
> based on the code review I think this fix should address such lockups.
>
> crash> bc 31
> PID: 747 TASK: ff1c6a1a007e8000 CPU: 31 COMMAND: "kworker/u72:2"
> --
> [exception RIP: ipoib_mcast_join_task+0x1b1]
> RIP: ffffffffc0944ac1 RSP: ff646f199a8c7e00 RFLAGS: 00000002
> RAX: 0000000000000000 RBX: ff1c6a1a04dc82f8 RCX: 0000000000000000
> work (&priv->mcast_task{,.work})
> RDX: ff1c6a192d60ac68 RSI: 0000000000000286 RDI: ff1c6a1a04dc8000
> &mcast->list
> RBP: ff646f199a8c7e90 R8: ff1c699980019420 R9: ff1c6a1920c9a000
> R10: ff646f199a8c7e00 R11: ff1c6a191a7d9800 R12: ff1c6a192d60ac00
> mcast
> R13: ff1c6a1d82200000 R14: ff1c6a1a04dc8000 R15: ff1c6a1a04dc82d8
> dev priv (&priv->lock) &priv->multicast_list (aka head)
> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
> --- <NMI exception stack> ---
> #5 [ff646f199a8c7e00] ipoib_mcast_join_task+0x1b1 at ffffffffc0944ac1 [ib_ipoib]
> #6 [ff646f199a8c7e98] process_one_work+0x1a7 at ffffffff9bf10967
>
> crash> rx ff646f199a8c7e68
> ff646f199a8c7e68: ff1c6a1a04dc82f8 <<< work = &priv->mcast_task.work
>
> crash> list -hO ipoib_dev_priv.multicast_list ff1c6a1a04dc8000
> (empty)
>
> crash> ipoib_dev_priv.mcast_task.work.func,mcast_mutex.owner.counter ff1c6a1a04dc8000
> mcast_task.work.func = 0xffffffffc0944910 <ipoib_mcast_join_task>,
> mcast_mutex.owner.counter = 0xff1c69998efec000
>
> crash> b 8
> PID: 8 TASK: ff1c69998efec000 CPU: 33 COMMAND: "kworker/u72:0"
> --
> #3 [ff646f1980153d50] wait_for_completion+0x96 at ffffffff9c7d7646
> #4 [ff646f1980153d90] ipoib_mcast_remove_list+0x56 at ffffffffc0944dc6 [ib_ipoib]
> #5 [ff646f1980153de8] ipoib_mcast_dev_flush+0x1a7 at ffffffffc09455a7 [ib_ipoib]
> #6 [ff646f1980153e58] __ipoib_ib_dev_flush+0x1a4 at ffffffffc09431a4 [ib_ipoib]
> #7 [ff646f1980153e98] process_one_work+0x1a7 at ffffffff9bf10967
>
> crash> rx ff646f1980153e68
> ff646f1980153e68: ff1c6a1a04dc83f0 <<< work = &priv->flush_light
>
> crash> ipoib_dev_priv.flush_light.func,broadcast ff1c6a1a04dc8000
> flush_light.func = 0xffffffffc0943820 <ipoib_ib_dev_flush_light>,
> broadcast = 0x0,
>
> The mcast(s) on the &remove_list (the remaining part of the ex &priv->multicast_list):
>
> crash> list -s ipoib_mcast.done.done ipoib_mcast.list -H ff646f1980153e10 | paste - -
> ff1c6a192bd0c200 done.done = 0x0,
> ff1c6a192d60ac00 done.done = 0x0,
>
> Reported-by: Yuya Fujita-bishamonten <fj-lsoft-rh-driver@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Daniel Vacek <neelx@xxxxxxxxxx>
> ---
> drivers/infiniband/ulp/ipoib/ipoib_multicast.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
> index 5b3154503bf4..8e4f2c8839be 100644
> --- a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
> +++ b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
> @@ -580,6 +580,7 @@ void ipoib_mcast_join_task(struct work_struct *work)
> }
> netif_addr_unlock_bh(dev);
>
> + mutex_lock(&priv->mcast_mutex);
> spin_lock_irq(&priv->lock);
> if (!test_bit(IPOIB_FLAG_OPER_UP, &priv->flags))
> goto out;
> @@ -634,6 +635,7 @@ void ipoib_mcast_join_task(struct work_struct *work)
> /* Found the next unjoined group */
> if (ipoib_mcast_join(dev, mcast)) {
> spin_unlock_irq(&priv->lock);
> + mutex_unlock(&priv->mcast_mutex);
> return;
> }
> } else if (!delay_until ||
> @@ -655,6 +657,7 @@ void ipoib_mcast_join_task(struct work_struct *work)
> ipoib_mcast_join(dev, mcast);
>
> spin_unlock_irq(&priv->lock);
> + mutex_unlock(&priv->mcast_mutex);
> }
>
> void ipoib_mcast_start_thread(struct net_device *dev)
> --
> 2.43.0
>