Re: [B.A.T.M.A.N.] [PATCH] batman-adv: Don't call sysfs_del_hardif() in atomic context

[Sven Eckelmann <sven.eckelmann@gmx.de>]

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Linus Lüssing wrote:
> sysfs_del_hardif invokes kobject_put, which might sleep. However, we
> are not allowed to sleep during a call_rcu. There is also no need to
> do the removal with an atomic call_rcu, as kobject_put only frees the
> kobject when there is no more reference to it anyway.
> 
> This commit basically revokes 7f32f2e8d97150ba5b80410dda86b01b0879fe8d,
> despite not reintroducing the synchronize_rcu, our rcu_barrier should
> handle this.

This is an extreme bad idea as we would free the object before the rcu grace 
period is over. This would mean that any parallel run through the list would 
probably access memory which is invalid. So this is a good way to crash your 
machine.

What makes you think that kobject_put sleeps? There is no code which proves 
it. The only reason would be that kobject_put -> kobject_release -> 
kobject_cleanup -> ... sleeps. Please complete that chain to show were the 
problem is. If it really sleeps then please only do the kobject related 
cleanup outside of call_rcu.

Best regards,
	Sven

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