linux-kernel - Re: [PATCH v12 22/22] selftests/vm: Fix deadlock in protection

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Date:   Mon, 26 Feb 2018 10:19:51 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     Ram Pai <linuxram@...ibm.com>
Cc:     shuahkh@....samsung.com, linux-kselftest@...r.kernel.org,
        mpe@...erman.id.au, linuxppc-dev@...ts.ozlabs.org,
        linux-mm@...ck.org, x86@...nel.org, linux-arch@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, akpm@...ux-foundation.org, dave.hansen@...el.com,
        benh@...nel.crashing.org, paulus@...ba.org,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        hbabu@...ibm.com, mhocko@...nel.org, bauerman@...ux.vnet.ibm.com,
        ebiederm@...ssion.com, arnd@...db.de
Subject: Re: [PATCH v12 22/22] selftests/vm: Fix deadlock in
 protection_keys.c

On Wed, 21 Feb 2018 17:55:41 -0800
Ram Pai <linuxram@...ibm.com> wrote:

> From: Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
> 
> The sig_chld() handler calls dprintf2() taking care of setting
> dprint_in_signal so that sigsafe_printf() won't call printf().
> Unfortunately, this precaution is is negated by dprintf_level(), which
> has a call to fflush().
>

fflush() is not the signal-safe function list, so this makes sense.
I wonder if fflush() is needed in sigsafe_printf()?

How about?

diff --git a/tools/testing/selftests/x86/pkey-helpers.h b/tools/testing/selftests/x86/pkey-helpers.h
index b3cb7670e026..2c3b39851f10 100644
--- a/tools/testing/selftests/x86/pkey-helpers.h
+++ b/tools/testing/selftests/x86/pkey-helpers.h
@@ -29,6 +29,7 @@ static inline void sigsafe_printf(const char *format, ...)
 	va_start(ap, format);
 	if (!dprint_in_signal) {
 		vprintf(format, ap);
+		fflush(NULL);				\
 	} else {
 		int ret;
 		int len = vsnprintf(dprint_in_signal_buffer,
@@ -49,7 +50,6 @@ static inline void sigsafe_printf(const char *format, ...)
 #define dprintf_level(level, args...) do {	\
 	if (level <= DEBUG_LEVEL)		\
 		sigsafe_printf(args);		\
-	fflush(NULL);				\
 } while (0)
 #define dprintf0(args...) dprintf_level(0, args)
 #define dprintf1(args...) dprintf_level(1, args)


But both are equivalent I guess, so
Acked-by: Balbir Singh <bsingharora@...il.com>