[v2,01/10] mmap locking API: initial implementation as rwsem wrappers

Commit Message

Michel Lespinasse March 27, 2020, 2:10 a.m. UTC

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 <[e-mail]>
---
 include/linux/mm.h        |  1 +
 include/linux/mmap_lock.h | 59 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 include/linux/mmap_lock.h

Comments

Jason Gunthorpe March 27, 2020, 12:16 p.m. UTC | #1

On Thu, Mar 26, 2020 at 07:10:49PM -0700, Michel Lespinasse wrote:

> +static inline bool mmap_is_locked(struct mm_struct *mm)
> +{
> +	return rwsem_is_locked(&mm->mmap_sem) != 0;
> +}

I didn't notice any callers to this in the series? Can it be deleted?

Jason

Michel Lespinasse March 27, 2020, 9:52 p.m. UTC | #2

On Fri, Mar 27, 2020 at 5:16 AM Jason Gunthorpe <[e-mail]> wrote:
>
> On Thu, Mar 26, 2020 at 07:10:49PM -0700, Michel Lespinasse wrote:
>
> > +static inline bool mmap_is_locked(struct mm_struct *mm)
> > +{
> > +     return rwsem_is_locked(&mm->mmap_sem) != 0;
> > +}
>
> I didn't notice any callers to this in the series? Can it be deleted?

Good catch. Yes, it should be deleted. There were 5 uses in v1 of this
patchset and I got rid of these in v2 of the patchset, but forgot to
actually remove the function definition here.

Patch

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c54fb96cb1e6..2f13c9198999 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..cffd25afe92b
--- /dev/null
+++ b/include/linux/mmap_lock.h
@@ -0,0 +1,59 @@ 
+#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_downgrade_write_lock(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);
+}
+
+static inline bool mmap_is_locked(struct mm_struct *mm)
+{
+	return rwsem_is_locked(&mm->mmap_sem) != 0;
+}
+
+#endif /* _LINUX_MMAP_LOCK_H */