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From:   Yangtao Li <tiny.windzz@gmail.com>
To:     akpm@linux-foundation.org, mhocko@suse.com, rientjes@google.com,
        dan.j.williams@intel.com, linux@dominikbrodowski.net,
        dave.hansen@linux.intel.com, dwmw@amazon.co.uk, mhocko@kernel.org
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Yangtao Li <tiny.windzz@gmail.com>
Subject: [PATCH] mm: mmap: remove verify_mm_writelocked()
Date:   Thu,  8 Nov 2018 12:48:56 -0500
Message-Id: <20181108174856.10811-1-tiny.windzz@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

We should get rid of this function. It no longer serves its purpose.This
is a historical artifact from 2005 where do_brk was called outside of
the core mm.We do have a proper abstraction in vm_brk_flags and that one
does the locking properly.So there is no need to use this function.

Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
---
 mm/mmap.c | 16 ----------------
 1 file changed, 16 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index f7cd9cb966c0..1cee506494d2 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2910,16 +2910,6 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 	return ret;
 }
 
-static inline void verify_mm_writelocked(struct mm_struct *mm)
-{
-#ifdef CONFIG_DEBUG_VM
-	if (unlikely(down_read_trylock(&mm->mmap_sem))) {
-		WARN_ON(1);
-		up_read(&mm->mmap_sem);
-	}
-#endif
-}
-
 /*
  *  this is really a simplified "do_mmap".  it only handles
  *  anonymous maps.  eventually we may be able to do some
@@ -2946,12 +2936,6 @@ static int do_brk_flags(unsigned long addr, unsigned long len, unsigned long fla
 	if (error)
 		return error;
 
-	/*
-	 * mm->mmap_sem is required to protect against another thread
-	 * changing the mappings in case we sleep.
-	 */
-	verify_mm_writelocked(mm);
-
 	/*
 	 * Clear old maps.  this also does some error checking for us
 	 */
-- 
2.17.0