mmap locking API: add mmap_read_trylock_non_owner()

Add a couple APIs used by kernel/bpf/stackmap.c only:
- mmap_read_trylock_non_owner()
- mmap_read_unlock_non_owner() (may be called from a work queue).

It's still not ideal that bpf/stackmap subverts the lock ownership in this
way.  Thanks to Peter Zijlstra for suggesting this API as the least-ugly
way of addressing this in the short term.

Signed-off-by: Michel Lespinasse <walken@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Laurent Dufour <ldufour@linux.ibm.com>
Cc: Liam Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ying Han <yinghan@google.com>
Link: http://lkml.kernel.org/r/20200520052908.204642-8-walken@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michel Lespinasse 2020-06-08 21:33:37 -07:00 committed by Linus Torvalds
parent aaa2cc56c1
commit 0cc55a0213
2 changed files with 19 additions and 12 deletions

View file

@ -56,4 +56,18 @@ static inline void mmap_read_unlock(struct mm_struct *mm)
up_read(&mm->mmap_sem);
}
static inline bool mmap_read_trylock_non_owner(struct mm_struct *mm)
{
if (down_read_trylock(&mm->mmap_sem)) {
rwsem_release(&mm->mmap_sem.dep_map, _RET_IP_);
return true;
}
return false;
}
static inline void mmap_read_unlock_non_owner(struct mm_struct *mm)
{
up_read_non_owner(&mm->mmap_sem);
}
#endif /* _LINUX_MMAP_LOCK_H */