linux-kernel - [PATCH 2/2] MIPS/c-r4k: do no use mmap_sem for gup

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Message-Id: <20190207053740.26915-3-dave@stgolabs.net>
Date:   Wed,  6 Feb 2019 21:37:40 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, dave@...olabs.net,
        linux-kernel@...r.kernel.org, Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>, linux-mips@...r.kernel.org,
        Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 2/2] MIPS/c-r4k: do no use mmap_sem for gup_fast()

It is well known that because the mm can internally
call the regular gup_unlocked if the lockless approach
fails and take the sem there, the caller must not hold
the mmap_sem already.

Fixes: e523f289fe4d (MIPS: c-r4k: Fix sigtramp SMP call to use kmap)
Cc: Ralf Baechle <ralf@...ux-mips.org>
Cc: Paul Burton <paul.burton@...s.com>
Cc: James Hogan <jhogan@...nel.org>
Cc: linux-mips@...r.kernel.org
Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 arch/mips/mm/c-r4k.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/arch/mips/mm/c-r4k.c b/arch/mips/mm/c-r4k.c
index cc4e17caeb26..38fe86928837 100644
--- a/arch/mips/mm/c-r4k.c
+++ b/arch/mips/mm/c-r4k.c
@@ -1034,11 +1034,9 @@ static void r4k_flush_cache_sigtramp(unsigned long addr)
 	struct flush_cache_sigtramp_args args;
 	int npages;
 
-	down_read(&current->mm->mmap_sem);
-
 	npages = get_user_pages_fast(addr, 1, 0, &args.page);
 	if (npages < 1)
-		goto out;
+		return;
 
 	args.mm = current->mm;
 	args.addr = addr;
@@ -1046,8 +1044,6 @@ static void r4k_flush_cache_sigtramp(unsigned long addr)
 	r4k_on_each_cpu(R4K_HIT, local_r4k_flush_cache_sigtramp, &args);
 
 	put_page(args.page);
-out:
-	up_read(&current->mm->mmap_sem);
 }
 
 static void r4k_flush_icache_all(void)
-- 
2.16.4