linux-kernel - [PATCH AUTOSEL for 4.15 73/78] clk: Don't touch hardware when reparenting during registration

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Message-ID: <20180308045525.7662-73-alexander.levin@microsoft.com>
Date:   Thu, 8 Mar 2018 04:56:33 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
CC:     Stephen Boyd <sboyd@...eaurora.org>,
        Michael Turquette <mturquette@...libre.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 4.15 73/78] clk: Don't touch hardware when
 reparenting during registration

From: Stephen Boyd <sboyd@...eaurora.org>

[ Upstream commit f8f8f1d04494d3a6546bee3f0618c4dba31d7b72 ]

The orphan clocks reparent operation shouldn't touch the hardware
if clocks are enabled, otherwise it may get a chance to disable a
newly registered critical clock which triggers the warning below.

Assuming we have two clocks: A and B, B is the parent of A.
Clock A has flag: CLK_OPS_PARENT_ENABLE
Clock B has flag: CLK_IS_CRITICAL

Step 1:
Clock A is registered, then it becomes orphan.

Step 2:
Clock B is registered. Before clock B reach the critical clock enable
operation, orphan A will find the newly registered parent B and do
reparent operation, then parent B will be finally disabled in
__clk_set_parent_after() due to CLK_OPS_PARENT_ENABLE flag as there's
still no users of B which will then trigger the following warning.

WARNING: CPU: 0 PID: 0 at drivers/clk/clk.c:597 clk_core_disable+0xb4/0xe0
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.11.0-rc1-00056-gdff1f66-dirty #1373
Hardware name: Generic DT based system
Backtrace:
[<c010c4bc>] (dump_backtrace) from [<c010c764>] (show_stack+0x18/0x1c)
 r6:600000d3 r5:00000000 r4:c0e26358 r3:00000000
[<c010c74c>] (show_stack) from [<c040599c>] (dump_stack+0xb4/0xe8)
[<c04058e8>] (dump_stack) from [<c0125c94>] (__warn+0xd8/0x104)
 r10:c0c21cd0 r9:c048aa78 r8:00000255 r7:00000009 r6:c0c1cd90 r5:00000000
 r4:00000000 r3:c0e01d34
[<c0125bbc>] (__warn) from [<c0125d74>] (warn_slowpath_null+0x28/0x30)
 r9:00000000 r8:ef00bf80 r7:c165ac4c r6:ef00bf80 r5:ef00bf80 r4:ef00bf80
[<c0125d4c>] (warn_slowpath_null) from [<c048aa78>] (clk_core_disable+0xb4/0xe0)
[<c048a9c4>] (clk_core_disable) from [<c048be88>] (clk_core_disable_lock+0x20/0x2c)
 r4:000000d3 r3:c0e0af00
[<c048be68>] (clk_core_disable_lock) from [<c048c224>] (clk_core_disable_unprepare+0x14/0x28)
 r5:00000000 r4:ef00bf80
[<c048c210>] (clk_core_disable_unprepare) from [<c048c270>] (__clk_set_parent_after+0x38/0x54)
 r4:ef00bd80 r3:000010a0
[<c048c238>] (__clk_set_parent_after) from [<c048daa8>] (clk_register+0x4d0/0x648)
 r6:ef00d500 r5:ef00bf80 r4:ef00bd80 r3:ef00bfd4
[<c048d5d8>] (clk_register) from [<c048dc30>] (clk_hw_register+0x10/0x1c)
 r9:00000000 r8:00000003 r7:00000000 r6:00000824 r5:00000001 r4:ef00d500
[<c048dc20>] (clk_hw_register) from [<c048e698>] (_register_divider+0xcc/0x120)
[<c048e5cc>] (_register_divider) from [<c048e730>] (clk_register_divider+0x44/0x54)
 r10:00000004 r9:00000003 r8:00000001 r7:00000000 r6:00000003 r5:00000001
 r4:f0810030
[<c048e6ec>] (clk_register_divider) from [<c0d3ff58>] (imx7ulp_clocks_init+0x558/0xe98)
 r7:c0e296f8 r6:c165c808 r5:00000000 r4:c165c808
[<c0d3fa00>] (imx7ulp_clocks_init) from [<c0d24db0>] (of_clk_init+0x118/0x1e0)
 r10:00000001 r9:c0e01f68 r8:00000000 r7:c0e01f60 r6:ef7f8974 r5:ef0035c0
 r4:00000006
[<c0d24c98>] (of_clk_init) from [<c0d04a50>] (time_init+0x2c/0x38)
 r10:efffed40 r9:c0d61a48 r8:c0e78000 r7:c0e07900 r6:ffffffff r5:c0e78000
 r4:00000000
[<c0d04a24>] (time_init) from [<c0d00b8c>] (start_kernel+0x218/0x394)
[<c0d00974>] (start_kernel) from [<6000807c>] (0x6000807c)
 r10:00000000 r9:410fc075 r8:6000406a r7:c0e0c930 r6:c0d61a44 r5:c0e07918
 r4:c0e78294

We know that the clk isn't enabled with any sort of prepare_count
here so we don't need to enable anything to prevent a race. And
we're holding the prepare mutex so set_rate/set_parent can't race
here either. Based on an earlier patch by Dong Aisheng.

Fixes: fc8726a2c021 ("clk: core: support clocks which requires parents enable (part 2)")
Cc: Michael Turquette <mturquette@...libre.com>
Cc: Shawn Guo <shawnguo@...nel.org>
Reported-by: Dong Aisheng <aisheng.dong@....com>
Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 drivers/clk/clk.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 0cca063f70e7..6c18fa7bcc23 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -2597,14 +2597,17 @@ static int __clk_core_init(struct clk_core *core)
 	 */
 	hlist_for_each_entry_safe(orphan, tmp2, &clk_orphan_list, child_node) {
 		struct clk_core *parent = __clk_init_parent(orphan);
+		unsigned long flags;
 
 		/*
 		 * we could call __clk_set_parent, but that would result in a
 		 * redundant call to the .set_rate op, if it exists
 		 */
 		if (parent) {
-			__clk_set_parent_before(orphan, parent);
-			__clk_set_parent_after(orphan, parent, NULL);
+			/* update the clk tree topology */
+			flags = clk_enable_lock();
+			clk_reparent(orphan, parent);
+			clk_enable_unlock(flags);
 			__clk_recalc_accuracies(orphan);
 			__clk_recalc_rates(orphan, 0);
 		}
-- 
2.14.1