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binder: reduce mmap_sem write-side lock

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binder has used write-side mmap_sem semaphore to release memory
mapped at address space of the process. However, right lock to
release pages is down_read, not down_write because page table lock
already protects the race for parallel freeing.

Please do not use mmap_sem write-side lock which is well known
contented lock.

Cc: Todd Kjos <tkjos@google.com>
Cc: Martijn Coenen <maco@android.com>
Cc: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Minchan Kim 2019-02-18 17:11:45 +09:00 committed by Greg Kroah-Hartman
parent 7c11df42d0
commit 3013bf62b6
1 changed files with 2 additions and 2 deletions
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4
drivers/android/binder_alloc.c
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@ -932,7 +932,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
if (!mmget_not_zero(alloc->vma_vm_mm))
goto err_mmget;
mm = alloc->vma_vm_mm;
if (!down_write_trylock(&mm->mmap_sem))
if (!down_read_trylock(&mm->mmap_sem))
goto err_down_write_mmap_sem_failed;
}
@ -946,7 +946,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
trace_binder_unmap_user_end(alloc, index);
up_write(&mm->mmap_sem);
up_read(&mm->mmap_sem);
mmput(mm);
}