kernel/notifier.c: double register detection
authorVasily Averin <vvs@virtuozzo.com>
Tue, 14 May 2019 22:42:28 +0000 (15:42 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 15 May 2019 02:52:49 +0000 (19:52 -0700)
commit831246570d34692e0550da952d0655bdcc985419
tree74ad4a7f33497497762446634c993b94a6ceed29
parent9012d011660ea5cf2a623e1de207a2bc0ca6936d
kernel/notifier.c: double register detection

By design notifiers can be registerd once only, 2nd register attempt
called by mistake silently corrupts notifiers list.

A few years ago I investigated described problem, the host was power
cycled because of notifier list corruption.  I've prepared this patch
and applied it to the OpenVZ kernel and sent this patch but nobody
commented on it.  Later it helped us to detect a similar problem in the
OpenVz kernel.

Mistakes with notifier registration can happen for example during
subsystem initialization from different namespaces, or because of a lost
unregister in the roll-back path on initialization failures.

The proposed check cannot prevent the described problem, however it
allows us to detect its reason quickly without coredump analysis.

Link: http://lkml.kernel.org/r/04127e71-4782-9bbb-fe5a-7c01e93a99b0@virtuozzo.com
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/notifier.c