vmalloc: back off when the current task is OOM-killed

Huge vmalloc allocation on heavy loaded node can lead to a global memory
shortage.  Task called vmalloc can have worst badness and be selected by
OOM-killer, however taken fatal signal does not interrupt allocation
cycle.  Vmalloc repeat page allocaions again and again, exacerbating the
crisis and consuming the memory freed up by another killed tasks.

After a successful completion of the allocation procedure, a fatal
signal will be processed and task will be destroyed finally.  However it
may not release the consumed memory, since the allocated object may have
a lifetime unrelated to the completed task.  In the worst case, this can
lead to the host will panic due to "Out of memory and no killable
processes..."

This patch allows OOM-killer to break vmalloc cycle, makes OOM more
effective and avoid host panic.  It does not check oom condition
directly, however, and breaks page allocation cycle when fatal signal
was received.

This may trigger some hidden problems, when caller does not handle
vmalloc failures, or when rollaback after failed vmalloc calls own
vmallocs inside.  However all of these scenarios are incorrect: vmalloc
does not guarantee successful allocation, it has never been called with
__GFP_NOFAIL and threfore either should not be used for any rollbacks or
should handle such errors correctly and not lead to critical failures.

Link: https://lkml.kernel.org/r/83efc664-3a65-2adb-d7c4-2885784cf109@virtuozzo.com


Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>