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* [PATCH v6] ANDROID: binder: change down_write to down_read
@ 2018-05-07 14:15 Minchan Kim
  2018-05-07 17:28 ` Joel Fernandes
  0 siblings, 1 reply; 10+ messages in thread
From: Minchan Kim @ 2018-05-07 14:15 UTC (permalink / raw)
  To: LKML
  Cc: Minchan Kim, Ganesh Mahendran, Joe Perches,
	Arve Hjønnevåg, Todd Kjos, Greg Kroah-Hartman,
	Martijn Coenen

binder_update_page_range needs down_write of mmap_sem because
vm_insert_page need to change vma->vm_flags to VM_MIXEDMAP unless
it is set. However, when I profile binder working, it seems
every binder buffers should be mapped in advance by binder_mmap.
It means we could set VM_MIXEDMAP in binder_mmap time which is
already hold a mmap_sem as down_write so binder_update_page_range
doesn't need to hold a mmap_sem as down_write.
Please use proper API down_read. It would help mmap_sem contention
problem as well as fixing down_write abuse.

Ganesh Mahendran tested app launching and binder throughput test
and he said he couldn't find any problem and I did binder latency
test per Greg KH request(Thanks Martijn to teach me how I can do)
I cannot find any problem, too.

Cc: Ganesh Mahendran <opensource.ganesh@gmail.com>
Cc: Joe Perches <joe@perches.com>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Todd Kjos <tkjos@google.com>
Reviewed-by: Martijn Coenen <maco@android.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 drivers/android/binder.c       | 4 +++-
 drivers/android/binder_alloc.c | 6 +++---
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 4eab5be3d00f..7b8e96f60719 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -4730,7 +4730,9 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
 		failure_string = "bad vm_flags";
 		goto err_bad_arg;
 	}
-	vma->vm_flags = (vma->vm_flags | VM_DONTCOPY) & ~VM_MAYWRITE;
+	vma->vm_flags |= VM_DONTCOPY | VM_MIXEDMAP;
+	vma->vm_flags &= ~VM_MAYWRITE;
+
 	vma->vm_ops = &binder_vm_ops;
 	vma->vm_private_data = proc;
 
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 5a426c877dfb..4f382d51def1 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -219,7 +219,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
 		mm = alloc->vma_vm_mm;
 
 	if (mm) {
-		down_write(&mm->mmap_sem);
+		down_read(&mm->mmap_sem);
 		vma = alloc->vma;
 	}
 
@@ -288,7 +288,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
 		/* vm_insert_page does not seem to increment the refcount */
 	}
 	if (mm) {
-		up_write(&mm->mmap_sem);
+		up_read(&mm->mmap_sem);
 		mmput(mm);
 	}
 	return 0;
@@ -321,7 +321,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
 	}
 err_no_vma:
 	if (mm) {
-		up_write(&mm->mmap_sem);
+		up_read(&mm->mmap_sem);
 		mmput(mm);
 	}
 	return vma ? -ENOMEM : -ESRCH;
-- 
2.17.0.441.gb46fe60e1d-goog

^ permalink raw reply	[flat|nested] 10+ messages in thread

end of thread, other threads:[~2018-05-17  3:23 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-05-07 14:15 [PATCH v6] ANDROID: binder: change down_write to down_read Minchan Kim
2018-05-07 17:28 ` Joel Fernandes
2018-05-08 10:51   ` Minchan Kim
2018-05-08 23:08     ` Joel Fernandes
2018-05-09  6:40       ` Minchan Kim
2018-05-09 23:19         ` Joel Fernandes
2018-05-15  6:27           ` Minchan Kim
2018-05-15  7:46             ` Martijn Coenen
2018-05-15  8:56               ` Minchan Kim
2018-05-17  3:23             ` Joel Fernandes

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