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Date:   Wed, 19 Jun 2019 18:09:40 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Vicente Bergas <vicencb@gmail.com>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>
Subject: Re: d_lookup: Unable to handle kernel paging request
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On Wed, Jun 19, 2019 at 06:51:51PM +0200, Vicente Bergas wrote:

> > What's your config, BTW?  SMP and DEBUG_SPINLOCK, specifically...
> 
> Hi Al,
> here it is:
> https://paste.debian.net/1088517

Aha...  So LIST_BL_LOCKMASK is 1 there (same as on distro builds)...

Hell knows - how about
static inline void hlist_bl_lock(struct hlist_bl_head *b)
{
	BUG_ON(((u32)READ_ONCE(*b)&~LIST_BL_LOCKMASK) == 0x01000000);
        bit_spin_lock(0, (unsigned long *)b);
}

and

static inline void hlist_bl_unlock(struct hlist_bl_head *b)
{
        __bit_spin_unlock(0, (unsigned long *)b);
	BUG_ON(((u32)READ_ONCE(*b)&~LIST_BL_LOCKMASK) == 0x01000000);
}

to see if we can narrow down where that happens?