x86/pkeys/selftests: Avoid printf-in-signal deadlocks

BugLink: http://bugs.launchpad.net/bugs/1794889
[ Upstream commit caf9eb6b4c82fc6cbd03697052ff22d97b0c377b ]

printf() and friends are unusable in signal handlers.  They deadlock.
The pkey selftest does not do any normal printing in signal handlers,
only extra debugging.  So, just print the format string so we get
*some* output when debugging.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Ellermen <mpe@ellerman.id.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20180509171344.C53FD2F3@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/tools/testing/selftests/x86/pkey-helpers.h b/tools/testing/selftests/x86/pkey-helpers.h
index b3cb7670e02661cd2ab66fd3da98b3940dd44c70..254e5436bdd9926091dc7c53bdd37be8bdb19121 100644 (file)
--- a/tools/testing/selftests/x86/pkey-helpers.h
+++ b/tools/testing/selftests/x86/pkey-helpers.h
@@ -26,30 +26,26 @@ static inline void sigsafe_printf(const char *format, ...)
 {
        va_list ap;
 
-       va_start(ap, format);
        if (!dprint_in_signal) {
+               va_start(ap, format);
                vprintf(format, ap);
+               va_end(ap);
        } else {
                int ret;
-               int len = vsnprintf(dprint_in_signal_buffer,
-                                   DPRINT_IN_SIGNAL_BUF_SIZE,
-                                   format, ap);
                /*
-                * len is amount that would have been printed,
-                * but actual write is truncated at BUF_SIZE.
+                * No printf() functions are signal-safe.
+                * They deadlock easily. Write the format
+                * string to get some output, even if
+                * incomplete.
                 */
-               if (len > DPRINT_IN_SIGNAL_BUF_SIZE)
-                       len = DPRINT_IN_SIGNAL_BUF_SIZE;
-               ret = write(1, dprint_in_signal_buffer, len);
+               ret = write(1, format, strlen(format));
                if (ret < 0)
-                       abort();
+                       exit(1);
        }
-       va_end(ap);
 }
 #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)