linux-kernel - Re: [PATCH] mtd: maps: pcmciamtd: fix possible sleep-in-atomic-context bugs in pcmciamtd_set

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Date:   Wed, 18 Dec 2019 18:28:13 +0100
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     miquel.raynal@...tlin.com, richard@....at, vigneshr@...com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: maps: pcmciamtd: fix possible
 sleep-in-atomic-context bugs in pcmciamtd_set_vpp()

On Wed, Dec 18, 2019 at 10:05:52PM +0800, Jia-Ju Bai wrote:
> The driver may sleep while holding a spinlock.
> The function call path (from bottom to top) in Linux 4.19 is:
> 
> drivers/pcmcia/pcmcia_resource.c, 312:
> 	mutex_lock in pcmcia_fixup_vpp
> drivers/mtd/maps/pcmciamtd.c, 309: 
> 	pcmcia_fixup_vpp in pcmciamtd_set_vpp
> drivers/mtd/maps/pcmciamtd.c, 306: 
> 	_raw_spin_lock_irqsave in pcmciamtd_set_vpp
> 
> drivers/pcmcia/pcmcia_resource.c, 312:
> 	mutex_lock in pcmcia_fixup_vpp
> drivers/mtd/maps/pcmciamtd.c, 312: 
> 	pcmcia_fixup_vpp in pcmciamtd_set_vpp
> drivers/mtd/maps/pcmciamtd.c, 306: 
> 	_raw_spin_lock_irqsave in pcmciamtd_set_vp
> 
> mutex_lock() may sleep at runtime.

Thanks for noticing this issue.

> To fix these bugs, pcmcia_fixup_vpp() is called without holding the
> spinlock.

I don't think that this is the right approach here -- we lose the protection
against races in calls to pcmcia_fixup_vpp(). Instead, we should change the
spinlock to a mutex, which seems to be sufficient here. Could you prepare
such a patch, please?

Thanks,
	Dominik