2022-04-18 04:56:08

by Duoming Zhou

Subject: [PATCH] drivers: net: hippi: Fix deadlock in rr_close()

There is a deadlock in rr_close(), which is shown below:

(Thread 1) | (Thread 2)
| rr_open()
rr_close() | add_timer()
spin_lock_irqsave() //(1) | (wait a time)
... | rr_timer()
del_timer_sync() | spin_lock_irqsave() //(2)
(wait timer to stop) | ...

We hold rrpriv->lock in position (1) of thread 1 and
use del_timer_sync() to wait timer to stop, but timer handler
also need rrpriv->lock in position (2) of thread 2.
As a result, rr_close() will block forever.

This patch extracts del_timer_sync() from the protection of
spin_lock_irqsave(), which could let timer handler to obtain
the needed lock.

Signed-off-by: Duoming Zhou <[email protected]>
---
drivers/net/hippi/rrunner.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/net/hippi/rrunner.c b/drivers/net/hippi/rrunner.c
index 16105292b14..74e845fa2e0 100644
--- a/drivers/net/hippi/rrunner.c
+++ b/drivers/net/hippi/rrunner.c
@@ -1355,7 +1355,9 @@ static int rr_close(struct net_device *dev)

rrpriv->fw_running = 0;

+ spin_unlock_irqrestore(&rrpriv->lock, flags);
del_timer_sync(&rrpriv->timer);
+ spin_lock_irqsave(&rrpriv->lock, flags);

writel(0, &regs->TxPi);
writel(0, &regs->IpRxPi);
--
2.17.1

2022-04-22 19:19:53

by patchwork-bot+netdevbpf

Subject: Re: [PATCH] drivers: net: hippi: Fix deadlock in rr_close()

Hello:

This patch was applied to netdev/net.git (master)
by Paolo Abeni <[email protected]>:

On Sun, 17 Apr 2022 20:55:19 +0800 you wrote:
> There is a deadlock in rr_close(), which is shown below:
>
> (Thread 1) | (Thread 2)
> | rr_open()
> rr_close() | add_timer()
> spin_lock_irqsave() //(1) | (wait a time)
> ... | rr_timer()
> del_timer_sync() | spin_lock_irqsave() //(2)
> (wait timer to stop) | ...
>
> [...]

Here is the summary with links:
- drivers: net: hippi: Fix deadlock in rr_close()
https://git.kernel.org/netdev/net/c/bc6de2878429

You are awesome, thank you!
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