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    Subject[PATCH 5.4 70/87] mmap locking API: initial implementation as rwsem wrappers
    Date
    From: Michel Lespinasse <walken@google.com>

    [ Upstream commit 9740ca4e95b43b91a4a848694a20d01ba6818f7b ]

    This patch series adds a new mmap locking API replacing the existing
    mmap_sem lock and unlocks. Initially the API is just implemente in terms
    of inlined rwsem calls, so it doesn't provide any new functionality.

    There are two justifications for the new API:

    - At first, it provides an easy hooking point to instrument mmap_sem
    locking latencies independently of any other rwsems.

    - In the future, it may be a starting point for replacing the rwsem
    implementation with a different one, such as range locks. This is
    something that is being explored, even though there is no wide concensus
    about this possible direction yet. (see
    https://patchwork.kernel.org/cover/11401483/)

    This patch (of 12):

    This change wraps the existing mmap_sem related rwsem calls into a new
    mmap locking API. There are two justifications for the new API:

    - At first, it provides an easy hooking point to instrument mmap_sem
    locking latencies independently of any other rwsems.

    - In the future, it may be a starting point for replacing the rwsem
    implementation with a different one, such as range locks.

    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: Davidlohr Bueso <dbueso@suse.de>
    Reviewed-by: Laurent Dufour <ldufour@linux.ibm.com>
    Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Matthew Wilcox <willy@infradead.org>
    Cc: Liam Howlett <Liam.Howlett@oracle.com>
    Cc: Jerome Glisse <jglisse@redhat.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Ying Han <yinghan@google.com>
    Cc: Jason Gunthorpe <jgg@ziepe.ca>
    Cc: John Hubbard <jhubbard@nvidia.com>
    Cc: Michel Lespinasse <walken@google.com>
    Link: http://lkml.kernel.org/r/20200520052908.204642-1-walken@google.com
    Link: http://lkml.kernel.org/r/20200520052908.204642-2-walken@google.com
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    include/linux/mm.h | 1 +
    include/linux/mmap_lock.h | 54 +++++++++++++++++++++++++++++++++++++++
    2 files changed, 55 insertions(+)
    create mode 100644 include/linux/mmap_lock.h

    diff --git a/include/linux/mm.h b/include/linux/mm.h
    index c125fea49752..d35c29d322d8 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -15,6 +15,7 @@
    #include <linux/atomic.h>
    #include <linux/debug_locks.h>
    #include <linux/mm_types.h>
    +#include <linux/mmap_lock.h>
    #include <linux/range.h>
    #include <linux/pfn.h>
    #include <linux/percpu-refcount.h>
    diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
    new file mode 100644
    index 000000000000..97ac53b66052
    --- /dev/null
    +++ b/include/linux/mmap_lock.h
    @@ -0,0 +1,54 @@
    +#ifndef _LINUX_MMAP_LOCK_H
    +#define _LINUX_MMAP_LOCK_H
    +
    +static inline void mmap_init_lock(struct mm_struct *mm)
    +{
    + init_rwsem(&mm->mmap_sem);
    +}
    +
    +static inline void mmap_write_lock(struct mm_struct *mm)
    +{
    + down_write(&mm->mmap_sem);
    +}
    +
    +static inline int mmap_write_lock_killable(struct mm_struct *mm)
    +{
    + return down_write_killable(&mm->mmap_sem);
    +}
    +
    +static inline bool mmap_write_trylock(struct mm_struct *mm)
    +{
    + return down_write_trylock(&mm->mmap_sem) != 0;
    +}
    +
    +static inline void mmap_write_unlock(struct mm_struct *mm)
    +{
    + up_write(&mm->mmap_sem);
    +}
    +
    +static inline void mmap_write_downgrade(struct mm_struct *mm)
    +{
    + downgrade_write(&mm->mmap_sem);
    +}
    +
    +static inline void mmap_read_lock(struct mm_struct *mm)
    +{
    + down_read(&mm->mmap_sem);
    +}
    +
    +static inline int mmap_read_lock_killable(struct mm_struct *mm)
    +{
    + return down_read_killable(&mm->mmap_sem);
    +}
    +
    +static inline bool mmap_read_trylock(struct mm_struct *mm)
    +{
    + return down_read_trylock(&mm->mmap_sem) != 0;
    +}
    +
    +static inline void mmap_read_unlock(struct mm_struct *mm)
    +{
    + up_read(&mm->mmap_sem);
    +}
    +
    +#endif /* _LINUX_MMAP_LOCK_H */
    --
    2.35.1


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