Patch "clockevents/tcb_clksrc: Prevent disabling an already disabled clock" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

clockevents/tcb_clksrc: Prevent disabling an already disabled clock

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
clockevents-tcb_clksrc-prevent-disabling-an-already-disabled-clock.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alexandre Belloni <[email protected]>
Date: Fri, 15 Jan 2016 11:34:21 +0100
Subject: clockevents/tcb_clksrc: Prevent disabling an already disabled clock

From: Alexandre Belloni <[email protected]>

commit f02b4b72d12cbae7020a959e2ed0410a464b4cc4 upstream.

clockevents_exchange_device is calling clockevents_shutdown() on the new clockenvents device but it may have never been enabled in the first place. This results in the tcb clock being disabled without being enabled first:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 1 at drivers/clk/clk.c:680 clk_disable+0x28/0x34()
Modules linked in:
CPU: 0 PID: 1 Comm: swapper Not tainted 4.4.0+ #6
Hardware name: Atmel AT91SAM9
[<c000f2b8>] (unwind_backtrace) from [<c000d01c>] (show_stack+0x10/0x14)
[<c000d01c>] (show_stack) from [<c00172f0>] (warn_slowpath_common+0x78/0xa0)
[<c00172f0>] (warn_slowpath_common) from [<c00173a8>] (warn_slowpath_null+0x18/0x20)
[<c00173a8>] (warn_slowpath_null) from [<c0361528>] (clk_disable+0x28/0x34)
[<c0361528>] (clk_disable) from [<c034d560>] (tc_shutdown+0x38/0x4c)
[<c034d560>] (tc_shutdown) from [<c0059ad4>] (clockevents_switch_state+0x38/0x6c)
[<c0059ad4>] (clockevents_switch_state) from [<c0059b18>] (clockevents_shutdown+0x10/0x24)
[<c0059b18>] (clockevents_shutdown) from [<c005a458>] (tick_check_new_device+0x84/0xac)
[<c005a458>] (tick_check_new_device) from [<c0059660>] (clockevents_register_device+0x7c/0x108)
[<c0059660>] (clockevents_register_device) from [<c06b5a68>] (tcb_clksrc_init+0x390/0x3e8)
[<c06b5a68>] (tcb_clksrc_init) from [<c00097cc>] (do_one_initcall+0x114/0x1d4)
[<c00097cc>] (do_one_initcall) from [<c069bd54>] (kernel_init_freeable+0xfc/0x1b8)
[<c069bd54>] (kernel_init_freeable) from [<c04c3818>] (kernel_init+0x8/0xe0)
[<c04c3818>] (kernel_init) from [<c000a410>] (ret_from_fork+0x14/0x24)
---[ end trace 0000000000000001 ]---

Check what state we were in before trying to disable the clock.

---
 drivers/clocksource/tcb_clksrc.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -98,7 +98,8 @@ static int tc_shutdown(struct clock_even
 
 	__raw_writel(0xff, regs + ATMEL_TC_REG(2, IDR));
 	__raw_writel(ATMEL_TC_CLKDIS, regs + ATMEL_TC_REG(2, CCR));
-	clk_disable(tcd->clk);
+	if (!clockevent_state_detached(d))
+		clk_disable(tcd->clk);
 
 	return 0;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/clockevents-tcb_clksrc-prevent-disabling-an-already-disabled-clock.patch