linux-kernel - Re: Sleeping BUG in khugepaged for i586

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Date:   Fri, 9 Jun 2017 09:43:48 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>,
        Larry Finger <Larry.Finger@...inger.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: Sleeping BUG in khugepaged for i586

On Fri 09-06-17 08:48:58, Vlastimil Babka wrote:
> On 06/08/2017 10:30 PM, Michal Hocko wrote:
> > But I guess you are primary after syncing the preemptive mode for 64 and
> > 32b systems, right? I agree that having a different model is more than
> > unfortunate because 32b gets much less testing coverage and so a risk of
> > introducing a new bug is just a matter of time. Maybe we should make
> > pte_offset_map disable preemption and currently noop pte_unmap to
> > preempt_enable. The overhead should be pretty marginal on x86_64 but not
> > all arches have per-cpu preempt count. So I am not sure we really want
> > to add this to just for the debugging purposes...
> 
> I think adding that overhead for everyone would be unfortunate. It would
> be acceptable, if it was done only for the config option that enables
> the might_sleep() checks (CONFIG_DEBUG_ATOMIC_SLEEP?)

That is certainly possible. But is it worth it?
arch/alpha/include/asm/pgtable.h:#define pte_offset_map(dir,addr)	pte_offset_kernel((dir),(addr))
arch/arc/include/asm/pgtable.h:#define pte_offset_map(dir, addr)		pte_offset(dir, addr)
arch/arm/include/asm/pgtable.h:#define pte_offset_map(pmd,addr)	(__pte_map(pmd) + pte_index(addr))
arch/arm64/include/asm/pgtable.h:#define pte_offset_map(dir,addr)	pte_offset_kernel((dir), (addr))
arch/arm64/include/asm/pgtable.h:#define pte_offset_map_nested(dir,addr)	pte_offset_kernel((dir), (addr))
arch/cris/include/asm/pgtable.h:#define pte_offset_map(dir, address) \
arch/frv/include/asm/pgtable.h:#define pte_offset_map(dir, address) \
arch/frv/include/asm/pgtable.h:#define pte_offset_map(dir, address) \
arch/hexagon/include/asm/pgtable.h:#define pte_offset_map(dir, address)                                    \
arch/hexagon/include/asm/pgtable.h:#define pte_offset_map_nested(pmd, addr) pte_offset_map(pmd, addr)
arch/ia64/include/asm/pgtable.h:#define pte_offset_map(dir,addr)	pte_offset_kernel(dir, addr)
arch/m32r/include/asm/pgtable.h:#define pte_offset_map(dir, address)	\
arch/m68k/include/asm/mcf_pgtable.h:#define pte_offset_map(pmdp, addr) ((pte_t *)__pmd_page(*pmdp) + \
arch/m68k/include/asm/motorola_pgtable.h:#define pte_offset_map(pmdp,address) ((pte_t *)__pmd_page(*pmdp) + (((address) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1)))
arch/m68k/include/asm/sun3_pgtable.h:#define pte_offset_map(pmd, address) ((pte_t *)page_address(pmd_page(*pmd)) + pte_index(address))
arch/metag/include/asm/pgtable.h:#define pte_offset_map(dir, address)		pte_offset_kernel(dir, address)
arch/metag/include/asm/pgtable.h:#define pte_offset_map_nested(dir, address)	pte_offset_kernel(dir, address)
arch/microblaze/include/asm/pgtable.h:#define pte_offset_map(dir, addr)		\
arch/mips/include/asm/pgtable-32.h:#define pte_offset_map(dir, address)					\
arch/mips/include/asm/pgtable-64.h:#define pte_offset_map(dir, address)					\
arch/mn10300/include/asm/pgtable.h:#define pte_offset_map(dir, address) \
arch/nios2/include/asm/pgtable.h:#define pte_offset_map(dir, addr)			\
arch/openrisc/include/asm/pgtable.h:#define pte_offset_map(dir, address)	        \
arch/openrisc/include/asm/pgtable.h:#define pte_offset_map_nested(dir, address)     \
arch/parisc/include/asm/pgtable.h:#define pte_offset_map(pmd, address) pte_offset_kernel(pmd, address)
arch/powerpc/include/asm/book3s/32/pgtable.h:#define pte_offset_map(dir, addr)		\
arch/powerpc/include/asm/book3s/64/pgtable.h:#define pte_offset_map(dir,addr)	pte_offset_kernel((dir), (addr))
arch/powerpc/include/asm/nohash/32/pgtable.h:#define pte_offset_map(dir, addr)		\
arch/powerpc/include/asm/nohash/64/pgtable.h:#define pte_offset_map(dir,addr)	pte_offset_kernel((dir), (addr))
arch/s390/include/asm/pgtable.h:#define pte_offset_map(pmd, address) pte_offset_kernel(pmd, address)
arch/score/include/asm/pgtable.h:#define pte_offset_map(dir, address)	\
arch/sh/include/asm/pgtable_32.h:#define pte_offset_map(dir, address)		pte_offset_kernel(dir, address)
arch/sh/include/asm/pgtable_64.h:#define pte_offset_map(dir,addr)	pte_offset_kernel(dir, addr)
arch/sparc/include/asm/pgtable_32.h:#define pte_offset_map(d, a)		pte_offset_kernel(d,a)
arch/sparc/include/asm/pgtable_64.h:#define pte_offset_map			pte_index
arch/tile/include/asm/pgtable.h:#define pte_offset_map(dir, address) pte_offset_kernel(dir, address)
arch/um/include/asm/pgtable.h:#define pte_offset_map(dir, address) \
arch/unicore32/include/asm/pgtable.h:#define pte_offset_map(dir, addr)	(pmd_page_vaddr(*(dir)) \
arch/x86/include/asm/pgtable_32.h:#define pte_offset_map(dir, address)					\
arch/x86/include/asm/pgtable_32.h:#define pte_offset_map(dir, address)					\
arch/x86/include/asm/pgtable_64.h:#define pte_offset_map(dir, address) pte_offset_kernel((dir), (address))
arch/xtensa/include/asm/pgtable.h:#define pte_offset_map(dir,addr)	pte_offset_kernel((dir),(addr))
include/linux/mm.h:#define pte_offset_map_lock(mm, pmd, address, ptlp)	\
-- 
Michal Hocko
SUSE Labs