• Thomas Gleixner's avatar
    mm/memory-hotplug: switch locking to a percpu rwsem · 3f906ba2
    Thomas Gleixner authored
    Andrey reported a potential deadlock with the memory hotplug lock and
    the cpu hotplug lock.
    
    The reason is that memory hotplug takes the memory hotplug lock and then
    calls stop_machine() which calls get_online_cpus().  That's the reverse
    lock order to get_online_cpus(); get_online_mems(); in mm/slub_common.c
    
    The problem has been there forever.  The reason why this was never
    reported is that the cpu hotplug locking had this homebrewn recursive
    reader writer semaphore construct which due to the recursion evaded the
    full lock dep coverage.  The memory hotplug code copied that construct
    verbatim and therefor has similar issues.
    
    Three steps to fix this:
    
    1) Convert the memory hotplug locking to a per cpu rwsem so the
       potential issues get reported proper by lockdep.
    
    2) Lock the online cpus in mem_hotplug_begin() before taking the memory
       hotplug rwsem and use stop_machine_cpuslocked() in the page_alloc
       code to avoid recursive locking.
    
    3) The cpu hotpluck locking in #2 causes a recursive locking of the cpu
       hotplug lock via __offline_pages() -> lru_add_drain_all(). Solve this
       by invoking lru_add_drain_all_cpuslocked() instead.
    
    Link: http://lkml.kernel.org/r/20170704093421.506836322@linutronix.deReported-by: default avatarAndrey Ryabinin <aryabinin@virtuozzo.com>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Acked-by: default avatarMichal Hocko <mhocko@suse.com>
    Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
    Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Davidlohr Bueso <dave@stgolabs.net>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    3f906ba2
memory_hotplug.c 50.1 KB