linux-kernel - Re: [PATCH] pstore: avoid recursive spinlocks in the oops_in

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Date:	Thu, 20 Sep 2012 16:25:36 -0700
From:	Anton Vorontsov <anton.vorontsov@...aro.org>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	"Liu, Chuansheng" <chuansheng.liu@...el.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"keescook@...omium.org" <keescook@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Colin Cross <ccross@...roid.com>
Subject: Re: [PATCH] pstore: avoid recursive spinlocks in the
 oops_in_progress case

On Thu, Sep 20, 2012 at 11:09:36PM +0000, Luck, Tony wrote:
> > Mm... why break?
> 
> We don't know what the back-end driver will do if we allow another call
> while a previous one is still in progress.  It might end up corrupting the
> backing non-volatile storage and losing some previously saved records.

True, but the lock is used to protect pstore->buf, I doubt that
any backend will actually want to grab it, no?

Since it is pstore that is handing the buffer to backend, it is
pstore's worry to do proper locking.

> Existing drivers (ERST and EFI) are dependent on f/w ... so things might
> work on some platforms, yet be horribly bad on others.
> 
> The patch as it was written converts a deadlock (hang) case into a "lose
> this log, but keep going" case. Which seems to be an improvement without
> taking any risks about what the backend will do.

But why backends should (or want/will want to) grab this lock?..

If a backend needs its own locking in ->write callback, then it'll
have to use its own lock, I guess.

Thanks,
Anton.
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