• Dan Williams's avatar
    mm: fix devm_memremap_pages crash, use mem_hotplug_{begin, done} · 70429b97
    Dan Williams authored
    commit f931ab47 upstream.
    Both arch_add_memory() and arch_remove_memory() expect a single threaded
    For example, arch/x86/mm/init_64.c::kernel_physical_mapping_init() does
    not hold any locks over this check and branch:
        if (pgd_val(*pgd)) {
        	pud = (pud_t *)pgd_page_vaddr(*pgd);
        	paddr_last = phys_pud_init(pud, __pa(vaddr),
        pud = alloc_low_page();
        paddr_last = phys_pud_init(pud, __pa(vaddr), __pa(vaddr_end),
    The result is that two threads calling devm_memremap_pages()
    simultaneously can end up colliding on pgd initialization.  This leads
    to crash signatures like the following where the loser of the race
    initializes the wrong pgd entry:
        BUG: unable to handle kernel paging request at ffff888ebfff0000
        IP: memcpy_erms+0x6/0x10
        PGD 2f8e8fc067 PUD 0 /* <---- Invalid PUD */
        Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
        CPU: 54 PID: 3818 Comm: systemd-udevd Not tainted 4.6.7+ #13
        task: ffff882fac290040 ti: ffff882f887a4000 task.ti: ffff882f887a4000
        RIP: memcpy_erms+0x6/0x10
        Call Trace:
          ? pmem_do_bvec+0x205/0x370 [nd_pmem]
          ? blk_queue_enter+0x3a/0x280
          pmem_rw_page+0x38/0x80 [nd_pmem]
    Hold the standard memory hotplug mutex over calls to
    Fixes: 41e94a85 ("add devm_memremap_pages")
    Link: http://lkml.kernel.org/r/148357647831.9498.12606007370121652979.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: default avatarDan Williams <dan.j.williams@intel.com>
    Cc: Christoph Hellwig <hch@lst.de>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
memremap.c 5.55 KB