| Message ID | 1358288444-30492-1-git-send-email-herton.krzesinski@canonical.com |
|---|---|
| State | New |
| Headers | show |
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c index be171ee..3c50ed9 100644 --- a/arch/powerpc/kernel/time.c +++ b/arch/powerpc/kernel/time.c @@ -750,13 +750,8 @@ void update_vsyscall(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)
This is a note to let you know that I have just added a patch titled powerpc/vdso: Remove redundant locking in to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.5.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Herton ------ From dd6b0a210c4b156e6d2fcf9e66c816e42466bd0b Mon Sep 17 00:00:00 2001 From: Shan Hai <shan.hai@windriver.com> Date: Thu, 8 Nov 2012 15:57:49 +0000 Subject: [PATCH] powerpc/vdso: Remove redundant locking in update_vsyscall_tz() commit ce73ec6db47af84d1466402781ae0872a9e7873c upstream. 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 <shan.hai@windriver.com> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com> --- arch/powerpc/kernel/time.c | 5 ----- 1 file changed, 5 deletions(-) -- 1.7.9.5