PM / Hibernate: Freeze kernel threads after preallocating memory

There is a problem with the current ordering of hibernate code which
leads to deadlocks in some filesystems' memory shrinkers.  Namely,
some filesystems use freezable kernel threads that are inactive when
the hibernate memory preallocation is carried out.  Those same
filesystems use memory shrinkers that may be triggered by the
hibernate memory preallocation.  If those memory shrinkers wait for
the frozen kernel threads, the hibernate process deadlocks (this
happens with XFS, for one example).

Apparently, it is not technically viable to redesign the filesystems
in question to avoid the situation described above, so the only
possible solution of this issue is to defer the freezing of kernel
threads until the hibernate memory preallocation is done, which is
implemented by this change.

Unfortunately, this requires the memory preallocation to be done
before the "prepare" stage of device freeze, so after this change the
only way drivers can allocate additional memory for their freeze
routines in a clean way is to use PM notifiers.

Reported-by: Christoph <cr2005@u-club.de>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

1 files changed, 0 insertions, 4 deletions

diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt
index 29b7a9817f5a..646a89e0c07d 100644
--- a/Documentation/power/devices.txt
+++ b/Documentation/power/devices.txt
@@ -281,10 +281,6 @@ When the system goes into the standby or memory sleep state, the phases are:
         time.)  Unlike the other suspend-related phases, during the prepare
         phase the device tree is traversed top-down.
 
-        In addition to that, if device drivers need to allocate additional
-        memory to be able to hadle device suspend correctly, that should be
-        done in the prepare phase.
-
         After the prepare callback method returns, no new children may be
         registered below the device.  The method may also prepare the device or
         driver in some way for the upcoming system power transition (for