linux-kernel - [PATCH AUTOSEL 4.4 29/29] parisc: Avoid calling faulthandler

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Date:   Mon, 17 Jan 2022 22:08:22 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     John David Anglin <dave.anglin@...l.net>,
        Helge Deller <deller@....de>, Sasha Levin <sashal@...nel.org>,
        James.Bottomley@...senPartnership.com, svens@...ckframe.org,
        akpm@...ux-foundation.org, mpe@...erman.id.au,
        rmk+kernel@...linux.org.uk, wangkefeng.wang@...wei.com,
        ebiederm@...ssion.com, linux-parisc@...r.kernel.org
Subject: [PATCH AUTOSEL 4.4 29/29] parisc: Avoid calling faulthandler_disabled() twice

From: John David Anglin <dave.anglin@...l.net>

[ Upstream commit 9e9d4b460f23bab61672eae397417d03917d116c ]

In handle_interruption(), we call faulthandler_disabled() to check whether the
fault handler is not disabled. If the fault handler is disabled, we immediately
call do_page_fault(). It then calls faulthandler_disabled(). If disabled,
do_page_fault() attempts to fixup the exception by jumping to no_context:

no_context:

        if (!user_mode(regs) && fixup_exception(regs)) {
                return;
        }

        parisc_terminate("Bad Address (null pointer deref?)", regs, code, address);

Apart from the error messages, the two blocks of code perform the same
function.

We can avoid two calls to faulthandler_disabled() by a simple revision
to the code in handle_interruption().

Note: I didn't try to fix the formatting of this code block.

Signed-off-by: John David Anglin <dave.anglin@...l.net>
Signed-off-by: Helge Deller <deller@....de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/parisc/kernel/traps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/parisc/kernel/traps.c b/arch/parisc/kernel/traps.c
index 6f61a17e2485a..55e7ba06511df 100644
--- a/arch/parisc/kernel/traps.c
+++ b/arch/parisc/kernel/traps.c
@@ -796,7 +796,7 @@ void notrace handle_interruption(int code, struct pt_regs *regs)
 	     * unless pagefault_disable() was called before.
 	     */
 
-	    if (fault_space == 0 && !faulthandler_disabled())
+	    if (faulthandler_disabled() || fault_space == 0)
 	    {
 		/* Clean up and return if in exception table. */
 		if (fixup_exception(regs))
-- 
2.34.1