From ce73ec6db47af84d1466402781ae0872a9e7873c Mon Sep 17 00:00:00 2001 From: Shan Hai Date: Thu, 8 Nov 2012 15:57:49 +0000 Subject: [PATCH 1/2] powerpc/vdso: Remove redundant locking in update_vsyscall_tz() The locking in update_vsyscall_tz() is not only unnecessary because the vdso code copies the data unproteced in __kernel_gettimeofday() but also introduces a hard to reproduce race condition between update_vsyscall() and update_vsyscall_tz(), which causes user space process to loop forever in vdso code. The following patch removes the locking from update_vsyscall_tz(). Locking is not only unnecessary because the vdso code copies the data unprotected in __kernel_gettimeofday() but also erroneous because updating the tb_update_count is not atomic and introduces a hard to reproduce race condition between update_vsyscall() and update_vsyscall_tz(), which further causes user space process to loop forever in vdso code. The below scenario describes the race condition, x==0 Boot CPU other CPU proc_P: x==0 timer interrupt update_vsyscall x==1 x++;sync settimeofday update_vsyscall_tz x==2 x++;sync x==3 sync;x++ sync;x++ proc_P: x==3 (loops until x becomes even) Because the ++ operator would be implemented as three instructions and not atomic on powerpc. A similar change was made for x86 in commit 6c260d58634 ("x86: vdso: Remove bogus locking in update_vsyscall_tz") Signed-off-by: Shan Hai CC: Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/kernel/time.c | 5 ----- 1 file changed, 5 deletions(-) diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c index b3b14352b05e..6f6b1cccc916 100644 --- a/arch/powerpc/kernel/time.c +++ b/arch/powerpc/kernel/time.c @@ -770,13 +770,8 @@ void update_vsyscall_old(struct timespec *wall_time, struct timespec *wtm, void update_vsyscall_tz(void) { - /* Make userspace gettimeofday spin until we're done. */ - ++vdso_data->tb_update_count; - smp_mb(); vdso_data->tz_minuteswest = sys_tz.tz_minuteswest; vdso_data->tz_dsttime = sys_tz.tz_dsttime; - smp_mb(); - ++vdso_data->tb_update_count; } static void __init clocksource_init(void) From e6449c9b2d90c1bd9a5985bf05ddebfd1631cd6b Mon Sep 17 00:00:00 2001 From: Gabor Juhos Date: Thu, 20 Dec 2012 03:44:28 +0000 Subject: [PATCH 2/2] powerpc: Add missing NULL terminator to avoid boot panic on PPC40x The missing NULL terminator can cause a panic on PPC405 boards during boot: Linux/PowerPC load: console=ttyS0,115200 root=/dev/mtdblock1 rootfstype=squashfs,jffs2 noinitrd init=/etc/preinit Finalizing device tree... flat tree at 0x6a5160 bootconsole [udbg0] enabled Page fault in user mode with in_atomic() = 1 mm = (null) NIP = c0275f50 MSR = fffffffe Oops: Weird page fault, sig: 11 [#1] PowerPC 40x Platform Modules linked in: NIP: c0275f50 LR: c0275f60 CTR: c0280000 REGS: c0275eb0 TRAP: 636f7265 Not tainted (3.7.1) MSR: fffffffe CR: c06a6190 XER: 00000001 TASK = c02662a8[0] 'swapper' THREAD: c0274000 GPR00: c0275ec0 c000c658 c027c4bf 00000000 c0275ee0 c000a0ec c020a1a8 c020a1f0 GPR08: c020f631 c020f404 c025f078 c025f080 c0275f10 Call Trace: ---[ end trace 31fd0ba7d8756001 ]--- Kernel panic - not syncing: Attempted to kill the idle task! The panic happens since commit 9597abe00c1bab2aedce6b49866bf6d1e81c9eed (sections: fix section conflicts in arch/powerpc), however the root cause of this is that the NULL terminator were not added in commit a4f740cf33f7f6c164bbde3c0cdbcc77b0c4997c (of/flattree: Add of_flat_dt_match() helper function). Cc: Grant Likely Cc: Signed-off-by: Gabor Juhos Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/platforms/40x/ppc40x_simple.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/platforms/40x/ppc40x_simple.c b/arch/powerpc/platforms/40x/ppc40x_simple.c index 969dddcf3320..8f3920e5a046 100644 --- a/arch/powerpc/platforms/40x/ppc40x_simple.c +++ b/arch/powerpc/platforms/40x/ppc40x_simple.c @@ -57,7 +57,8 @@ static const char * const board[] __initconst = { "amcc,makalu", "apm,klondike", "est,hotfoot", - "plathome,obs600" + "plathome,obs600", + NULL }; static int __init ppc40x_probe(void)