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    SubjectRe: [PATCH 4.14 023/159] mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y
    On Fri, Dec 22, 2017 at 08:22:09PM +0530, Naresh Kamboju wrote:
    > On 22 December 2017 at 19:48, Dan Rue <dan.rue@linaro.org> wrote:
    > > On Fri, Dec 22, 2017 at 09:45:08AM +0100, Greg Kroah-Hartman wrote:
    > >> 4.14-stable review patch. If anyone has any objections, please let me know.
    > >>
    > >> ------------------
    > >>
    > >> From: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    > >>
    > >> commit 83e3c48729d9ebb7af5a31a504f3fd6aff0348c4 upstream.
    > >>
    > >> Size of the mem_section[] array depends on the size of the physical address space.
    > >>
    > >> In preparation for boot-time switching between paging modes on x86-64
    > >> we need to make the allocation of mem_section[] dynamic, because otherwise
    > >> we waste a lot of RAM: with CONFIG_NODE_SHIFT=10, mem_section[] size is 32kB
    > >> for 4-level paging and 2MB for 5-level paging mode.
    > >>
    > >> The patch allocates the array on the first call to sparse_memory_present_with_active_regions().
    > >>
    > >> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    > >> Cc: Andrew Morton <akpm@linux-foundation.org>
    > >> Cc: Andy Lutomirski <luto@amacapital.net>
    > >> Cc: Borislav Petkov <bp@suse.de>
    > >> Cc: Cyrill Gorcunov <gorcunov@openvz.org>
    > >> Cc: Linus Torvalds <torvalds@linux-foundation.org>
    > >> Cc: Peter Zijlstra <peterz@infradead.org>
    > >> Cc: Thomas Gleixner <tglx@linutronix.de>
    > >> Cc: linux-mm@kvack.org
    > >> Link: http://lkml.kernel.org/r/20170929140821.37654-2-kirill.shutemov@linux.intel.com
    > >> Signed-off-by: Ingo Molnar <mingo@kernel.org>
    > >> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > >
    > > This patch causes a boot failure on arm64.
    > >
    > > Please drop this patch, or pick up the fix in:
    > >
    > > commit 629a359bdb0e0652a8227b4ff3125431995fec6e
    > > Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    > > Date: Tue Nov 7 11:33:37 2017 +0300
    > >
    > > mm/sparsemem: Fix ARM64 boot crash when CONFIG_SPARSEMEM_EXTREME=y
    > >
    > > See https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1527427.html
    >
    > +1.
    > Boot failed on arm64 without 629a359b
    > mm/sparsemem: Fix ARM64 boot crash when CONFIG_SPARSEMEM_EXTREME=y
    >
    > Boot Error log:
    > --------------------
    > [ 0.000000] Unable to handle kernel NULL pointer dereference at
    > virtual address 00000000
    > [ 0.000000] Mem abort info:
    > [ 0.000000] Exception class = DABT (current EL), IL = 32 bits
    > [ 0.000000] SET = 0, FnV = 0
    > [ 0.000000] EA = 0, S1PTW = 0
    > [ 0.000000] Data abort info:
    > [ 0.000000] ISV = 0, ISS = 0x00000004
    > [ 0.000000] CM = 0, WnR = 0
    > [ 0.000000] [0000000000000000] user address but active_mm is swapper
    > [ 0.000000] Internal error: Oops: 96000004 [#1] PREEMPT SMP
    > [ 0.000000] Modules linked in:
    > [ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.14.9-rc1 #1
    > [ 0.000000] Hardware name: ARM Juno development board (r2) (DT)
    > [ 0.000000] task: ffff0000091d9380 task.stack: ffff0000091c0000
    > [ 0.000000] PC is at memory_present+0x64/0xf4
    > [ 0.000000] LR is at memory_present+0x38/0xf4
    > [ 0.000000] pc : [<ffff0000090a1f54>] lr : [<ffff0000090a1f28>]
    > pstate: 800000c5
    > [ 0.000000] sp : ffff0000091c3e80
    >
    > More information,
    > https://pastebin.com/KambxUwb

    -rc2 is out with the fix, hopefully that survives longer :)

    thanks,

    greg k-h

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