linux-kernel - Re: [mainline][Memory off/on][83e3c48] kernel Oops with memory hot-unplug on ppc

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Date:   Mon, 19 Feb 2018 16:56:46 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Abdul Haleem <abdhalee@...ux.vnet.ibm.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>, linux-mm@...ck.org,
        kirill.shutemov@...ux.intel.com, mpe <mpe@...erman.id.au>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        sachinp <sachinp@...ux.vnet.ibm.com>
Subject: Re: [mainline][Memory off/on][83e3c48] kernel Oops with memory
 hot-unplug on ppc

On Mon, Feb 19, 2018 at 02:47:35PM +0100, Michal Hocko wrote:
> [CC Kirill - I have a vague recollection that there were some follow ups
>  for 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for
>  CONFIG_SPARSEMEM_EXTREME=y"). Does any of them apply to this issue?]

All fixups are in v4.15.

> On Mon 05-02-18 19:54:24, Abdul Haleem wrote:
> > 
> > Greetings,
> > 
> > Kernel Oops seen when memory hot-unplug on powerpc mainline kernel.
> > 
> > Machine: Power6 PowerVM ppc64
> > Kernel: 4.15.0
> > Config: attached
> > gcc: 4.8.2
> > Test: Memory hot-unplug of a memory block
> > echo offline > /sys/devices/system/memory/memory<x>/state
> > 
> > The faulty instruction address points to the code path:
> > 
> > # gdb -batch vmlinux -ex 'list *(0xc000000000238330)'
> > 0xc000000000238330 is in get_pfnblock_flags_mask
> > (./include/linux/mmzone.h:1157).
> > 1152	#endif
> > 1153	
> > 1154	static inline struct mem_section *__nr_to_section(unsigned long nr)
> > 1155	{
> > 1156	#ifdef CONFIG_SPARSEMEM_EXTREME
> > 1157		if (!mem_section)
> > 1158			return NULL;
> > 1159	#endif
> > 1160		if (!mem_section[SECTION_NR_TO_ROOT(nr)])
> > 1161			return NULL;
> > 
> > 
> > The code was first introduced with commit( 83e3c48: mm/sparsemem:
> > Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y)

Any chance to bisect it?

Could you check if the commit just before 83e3c48729d9 is fine?

-- 
 Kirill A. Shutemov