• Minchan Kim's avatar
    memory-hotplug: don't replace lowmem pages with highmem · 74c08f98
    Minchan Kim authored
    The changelog for commit 6a6dccba ("mm: cma: don't replace lowmem
    pages with highmem") mentioned that lowmem pages can be replaced by
    highmem pages during CMA migration.  6a6dccba fixed that issue.
    
    Quote from that changelog:
    
    :   The filesystem layer expects pages in the block device's mapping to not
    :   be in highmem (the mapping's gfp mask is set in bdget()), but CMA can
    :   currently replace lowmem pages with highmem pages, leading to crashes in
    :   filesystem code such as the one below:
    :
    :     Unable to handle kernel NULL pointer dereference at virtual address 00000400
    :     pgd = c0c98000
    :     [00000400] *pgd=00c91831, *pte=00000000, *ppte=00000000
    :     Internal error: Oops: 817 [#1] PREEMPT SMP ARM
    :     CPU: 0    Not tainted  (3.5.0-rc5+ #80)
    :     PC is at __memzero+0x24/0x80
    :     ...
    :     Process fsstress (pid: 323, stack limit = 0xc0cbc2f0)
    :     Backtrace:
    :     [<c010e3f0>] (ext4_getblk+0x0/0x180) from [<c010e58c>] (ext4_bread+0x1c/0x98)
    :     [<c010e570>] (ext4_bread+0x0/0x98) from [<c0117944>] (ext4_mkdir+0x160/0x3bc)
    :      r4:c15337f0
    :     [<c01177e4>] (ext4_mkdir+0x0/0x3bc) from [<c00c29e0>] (vfs_mkdir+0x8c/0x98)
    :     [<c00c2954>] (vfs_mkdir+0x0/0x98) from [<c00c2a60>] (sys_mkdirat+0x74/0xac)
    :      r6:00000000 r5:c152eb40 r4:000001ff r3:c14b43f0
    :     [<c00c29ec>] (sys_mkdirat+0x0/0xac) from [<c00c2ab8>] (sys_mkdir+0x20/0x24)
    :      r6:beccdcf0 r5:00074000 r4:beccdbbc
    :     [<c00c2a98>] (sys_mkdir+0x0/0x24) from [<c000e3c0>] (ret_fast_syscall+0x0/0x30)
    
    Memory-hotplug has same problem as CMA has so the same fix can be applied
    to memory-hotplug as well.
    
    Fix it by reusing.
    Signed-off-by: default avatarMinchan Kim <minchan@kernel.org>
    Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Reviewed-by: default avatarYasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
    Acked-by: default avatarMichal Nazarewicz <mina86@mina86.com>
    Cc: Marek Szyprowski <m.szyprowski@samsung.com>
    Cc: Wen Congyang <wency@cn.fujitsu.com>
    Acked-by: default avatarDavid Rientjes <rientjes@google.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    74c08f98
memory_hotplug.c 24.4 KB