From: Minchan Kim <minchan@kernel.org>
To: LKML <linux-kernel@vger.kernel.org>
Cc: "Minchan Kim" <minchan@kernel.org>,
"Ganesh Mahendran" <opensource.ganesh@gmail.com>,
"Joe Perches" <joe@perches.com>,
"Arve Hjønnevåg" <arve@android.com>,
"Todd Kjos" <tkjos@google.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Martijn Coenen" <maco@android.com>
Subject: [PATCH v6] ANDROID: binder: change down_write to down_read
Date: Mon, 7 May 2018 23:15:37 +0900 [thread overview]
Message-ID: <20180507141537.4855-1-minchan@kernel.org> (raw)
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
next reply other threads:[~2018-05-07 14:15 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-07 14:15 Minchan Kim [this message]
2018-05-07 17:28 ` [PATCH v6] ANDROID: binder: change down_write to down_read 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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