[PATCH 2/2] powerpc/pseries: Avoid deadlock on removing ddw

[Gavin Shan]

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>] \
 .__blocking_notifier_call_chain+0x40/0x78

but task is already holding lock:
 ((of_reconfig_chain).rwsem){.+.+..}, at: [<c000000000091890>] \
 .__blocking_notifier_call_chain+0x40/0x78

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

       CPU0
       ----
  lock((of_reconfig_chain).rwsem);
  lock((of_reconfig_chain).rwsem);
 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by drmgr/2273:
 #0:  (sb_writers#4){.+.+.+}, at: [<c0000000001cbe70>] \
      .vfs_write+0xb0/0x1f8
 #1:  ((of_reconfig_chain).rwsem){.+.+..}, at: [<c000000000091890>] \
      .__blocking_notifier_call_chain+0x40/0x78

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

Cc: stable at vger.kernel.org
Signed-off-by: Gavin Shan <gwshan at linux.vnet.ibm.com>
---
 arch/powerpc/platforms/pseries/iommu.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
index 33b552f..4642d6a 100644
--- 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 *str)
 
 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_node *np)
 			np->full_name, ret, ddw_avail[2], liobn);
 
 delprop:
-	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(void)
 		window = kzalloc(sizeof(*window), GFP_KERNEL);
 		if (!window || len < sizeof(struct dynamic_dma_window_prop)) {
 			kfree(window);
-			remove_ddw(pdn);
+			remove_ddw(pdn, true);
 			continue;
 		}
 
@@ -1045,7 +1046,7 @@ out_free_window:
 	kfree(window);
 
 out_clear_window:
-	remove_ddw(pdn);
+	remove_ddw(pdn, true);
 
 out_free_prop:
 	kfree(win64->name);
@@ -1255,7 +1256,14 @@ static int iommu_reconfig_notifier(struct notifier_block *nb, unsigned long acti
 
 	switch (action) {
 	case OF_RECONFIG_DETACH_NODE:
-		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);
 
-- 
1.8.3.2