[RFC PATCH 0/2] kernel/power: fix swap device reference handling in hibernation swap path

[Youngjun Park <youngjun.park@lge.com>]

This series addresses two issues in the hibernation swap path.

First, grabbing and releasing the swap device reference on every slot
allocation is inefficient across the entire hibernation swap path.

Second, in the uswsusp path, only the swap type value is retrieved at
lookup time without holding a reference. If swapoff races after the
type is acquired, subsequent slot allocations operate on a stale swap
device.

The fix is to hold the swap device reference from the point the swap
device is looked up, and release it once at each exit path.

  Patch 1: Release the reference immediately after each slot allocation
            as a preparatory step.
  Patch 2: Lift the reference acquisition to the lookup site and place
            put_swap_device_by_type() at all relevant cleanup paths in
            swap.c and user.c.

This series is based on mm-new.

I'm sending this as RFC because my familiarity with the kernel/power
and snapshot paths is limited. I believe the approach is reasonable,
but I'd appreciate any feedback before moving forward with proper
testing and a formal submission.

Thanks,
Youngjun Park

Youngjun Park (2):
  mm/swap: release swap reference on each hibernation slot allocation
  kernel/power: hold swap device reference across hibernation swap
    operation

 include/linux/swap.h |  1 +
 kernel/power/swap.c  | 12 +++++++---
 kernel/power/user.c  |  9 +++++++-
 mm/swapfile.c        | 55 ++++++++++++++++++++++----------------------
 4 files changed, 45 insertions(+), 32 deletions(-)

-- 
2.34.1