[PATCH 0/18] change mmap_sem taken for write killable v2

[Michal Hocko]

Hi,
The previous version of the series was posted here [0]. There were
no large changes since then. I have rebased the series on top of the
current linux-next (next-20160426) and added few clarifications based on
the review feedback and acks/reviewed-by.

This is a follow up work for oom_reaper [1]. As the async OOM killing
depends on oom_sem for read we would really appreciate if a holder
for write didn't stood in the way. This patchset is changing many of
down_write calls to be killable to help those cases when the writer
is blocked and waiting for readers to release the lock and so help
__oom_reap_task to process the oom victim.

Most of the patches are really trivial because the lock is help from a
shallow syscall paths where we can return EINTR trivially and allow the
current task to die (note that EINTR will never get to the userspace as
the task has fatal signal pending). Others seem to be easy as well as
the callers are already handling fatal errors and bail and return to
userspace which should be sufficient to handle the failure gracefully. I
am not familiar with all those code paths so a deeper review is really
appreciated.

As this work is touching more areas which are not directly connected I
have tried to keep the CC list as small as possible and people who I
believed would be familiar are CCed only to the specific patches (all
should have received the cover though).

This patchset is based on linux-next and it depends on
down_write_killable for rw_semaphores which got merged into tip
locking/rwsem branch and it is merged into this next tree.  I guess
it would be easiest to route these patches via mmotm because of the
dependency on the tip tree but if respective maintainers prefer other
way I have no objections.

I haven't covered all the mmap_write(mm->mmap_sem) instances here

$ git grep "down_write(.*\<mmap_sem\>)" next/master | wc -l
98
$ git grep "down_write(.*\<mmap_sem\>)" | wc -l
62

I have tried to cover those which should be relatively easy to review in
this series because this alone should be a nice improvement. Other places
can be changed on top.

Any feedback is highly appreciated.

---
[0] http://lkml.kernel.org/r/1456752417-9626-1-git-send-email-mhocko@xxxxxxxxxx
[1] http://lkml.kernel.org/r/1452094975-551-1-git-send-email-mhocko@xxxxxxxxxx
[2] http://lkml.kernel.org/r/1456750705-7141-1-git-send-email-mhocko@xxxxxxxxxx