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Date:	Mon, 15 Sep 2014 12:25:24 -0700
From:	Greg Kroah-Hartman <>
Cc:	Greg Kroah-Hartman <>,, Gavin Shan <>,
	Benjamin Herrenschmidt <>
Subject: [PATCH 3.14 024/114] powerpc/pseries: Avoid deadlock on removing ddw

3.14-stable review patch.  If anyone has any objections, please let me know.


From: Gavin Shan <>

commit 5efbabe09d986f25c02d19954660238fcd7f008a upstream.

Function remove_ddw() could be called in of_reconfig_notifier and
we potentially remove the dynamic DMA window property, which invokes
of_reconfig_notifier again. Eventually, it leads to the deadlock as
following backtrace shows.

The patch fixes the above issue by deferring releasing the dynamic
DMA window property while releasing the device node.

[ INFO: possible recursive locking detected ]
3.16.0+ #428 Tainted: G        W
drmgr/2273 is trying to acquire lock:
 ((of_reconfig_chain).rwsem){.+.+..}, at: [<c000000000091890>] \

but task is already holding lock:
 ((of_reconfig_chain).rwsem){.+.+..}, at: [<c000000000091890>] \

other info that might help us debug this:
 Possible unsafe locking scenario:

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by drmgr/2273:
 #0:  (sb_writers#4){.+.+.+}, at: [<c0000000001cbe70>] \
 #1:  ((of_reconfig_chain).rwsem){.+.+..}, at: [<c000000000091890>] \

stack backtrace:
CPU: 17 PID: 2273 Comm: drmgr Tainted: G        W     3.16.0+ #428
Call Trace:
[c0000000137e7000] [c000000000013d9c] .show_stack+0x88/0x148 (unreliable)
[c0000000137e70b0] [c00000000083cd34] .dump_stack+0x7c/0x9c
[c0000000137e7130] [c0000000000b8afc] .__lock_acquire+0x128c/0x1c68
[c0000000137e7280] [c0000000000b9a4c] .lock_acquire+0xe8/0x104
[c0000000137e7350] [c00000000083588c] .down_read+0x4c/0x90
[c0000000137e73e0] [c000000000091890] .__blocking_notifier_call_chain+0x40/0x78
[c0000000137e7490] [c000000000091900] .blocking_notifier_call_chain+0x38/0x48
[c0000000137e7520] [c000000000682a28] .of_reconfig_notify+0x34/0x5c
[c0000000137e75b0] [c000000000682a9c] .of_property_notify+0x4c/0x54
[c0000000137e7650] [c000000000682bf0] .of_remove_property+0x30/0xd4
[c0000000137e76f0] [c000000000052a44] .remove_ddw+0x144/0x168
[c0000000137e7790] [c000000000053204] .iommu_reconfig_notifier+0x30/0xe0
[c0000000137e7820] [c00000000009137c] .notifier_call_chain+0x6c/0xb4
[c0000000137e78c0] [c0000000000918ac] .__blocking_notifier_call_chain+0x5c/0x78
[c0000000137e7970] [c000000000091900] .blocking_notifier_call_chain+0x38/0x48
[c0000000137e7a00] [c000000000682a28] .of_reconfig_notify+0x34/0x5c
[c0000000137e7a90] [c000000000682e14] .of_detach_node+0x44/0x1fc
[c0000000137e7b40] [c0000000000518e4] .ofdt_write+0x3ac/0x688
[c0000000137e7c20] [c000000000238430] .proc_reg_write+0xb8/0xd4
[c0000000137e7cd0] [c0000000001cbeac] .vfs_write+0xec/0x1f8
[c0000000137e7d70] [c0000000001cc3b0] .SyS_write+0x58/0xa0
[c0000000137e7e30] [c00000000000a064] syscall_exit+0x0/0x98

Signed-off-by: Gavin Shan <>
Signed-off-by: Benjamin Herrenschmidt <>
Signed-off-by: Greg Kroah-Hartman <>

 arch/powerpc/platforms/pseries/iommu.c |   20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

--- a/arch/powerpc/platforms/pseries/iommu.c
+++ b/arch/powerpc/platforms/pseries/iommu.c
@@ -721,13 +721,13 @@ static int __init disable_ddw_setup(char
 early_param("disable_ddw", disable_ddw_setup);
-static void remove_ddw(struct device_node *np)
+static void remove_ddw(struct device_node *np, bool remove_prop)
 	struct dynamic_dma_window_prop *dwp;
 	struct property *win64;
 	const u32 *ddw_avail;
 	u64 liobn;
-	int len, ret;
+	int len, ret = 0;
 	ddw_avail = of_get_property(np, "ibm,ddw-applicable", &len);
 	win64 = of_find_property(np, DIRECT64_PROPNAME, NULL);
@@ -761,7 +761,8 @@ static void remove_ddw(struct device_nod
 			np->full_name, ret, ddw_avail[2], liobn);
-	ret = of_remove_property(np, win64);
+	if (remove_prop)
+		ret = of_remove_property(np, win64);
 	if (ret)
 		pr_warning("%s: failed to remove direct window property: %d\n",
 			np->full_name, ret);
@@ -805,7 +806,7 @@ static int find_existing_ddw_windows(voi
 		window = kzalloc(sizeof(*window), GFP_KERNEL);
 		if (!window || len < sizeof(struct dynamic_dma_window_prop)) {
-			remove_ddw(pdn);
+			remove_ddw(pdn, true);
@@ -1045,7 +1046,7 @@ out_free_window:
-	remove_ddw(pdn);
+	remove_ddw(pdn, true);
@@ -1255,7 +1256,14 @@ static int iommu_reconfig_notifier(struc
 	switch (action) {
-		remove_ddw(np);
+		/*
+		 * Removing the property will invoke the reconfig
+		 * notifier again, which causes dead-lock on the
+		 * read-write semaphore of the notifier chain. So
+		 * we have to remove the property when releasing
+		 * the device node.
+		 */
+		remove_ddw(np, false);
 		if (pci && pci->iommu_table)
 			iommu_free_table(pci->iommu_table, np->full_name);

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