[PATCH v2 0/2] vma_start_write_killable

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

When we added the VMA lock, we made a major oversight in not adding a
killable variant.  That can run us into trouble where a thread takes
the VMA lock for read (eg handling a page fault) and then goes out to
lunch for an hour (eg doing reclaim).  Another thread tries to modify
the VMA, taking the mmap_lock for write, then attempts to lock the VMA
for write.  That blocks on the first thread, and ensures that every
other page fault now tries to take the mmap_lock for read.  Because
everything's in an uninterruptible sleep, we can't kill the task,
which makes me angry.

This patch set just adds vma_start_write_killable() and converts one
caller to use it.  Most users are somewhat tricky to convert, so expect
follow-up individual patches per call-site which need careful analysis
to make sure we've done proper cleanup.

v2:
 - Document the return value from __vma_start_write() (Suren)
 - Call rwsem_release() on failure to make lockdep happy
 - Reformat the prototype for vma_start_write_killable() to make
   both Suren & me happy
 - Add the kernel-doc for vma_start_write_killable() to
   Documentation/mm/process_addrs.rst
 - Collect R-b from Suren & Liam (thanks!)

Matthew Wilcox (Oracle) (2):
  mm: Add vma_start_write_killable()
  mm: Use vma_start_write_killable() in dup_mmap()

 Documentation/mm/process_addrs.rst |  9 +++++++-
 include/linux/mmap_lock.h          | 30 ++++++++++++++++++++++++--
 mm/mmap.c                          | 12 +++--------
 mm/mmap_lock.c                     | 34 ++++++++++++++++++++++--------
 tools/testing/vma/vma_internal.h   |  8 +++++++
 5 files changed, 72 insertions(+), 21 deletions(-)

-- 
2.47.2