linux-kernel - [PATCH] swiotlb: ensure io_tlb_default

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Date:   Fri,  8 Jul 2022 18:08:11 +0100
From:   Ben Dooks <ben.dooks@...ive.com>
To:     linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
        iommu@...ts.linux-foundation.org
Cc:     Sudip Mukherjee <sudip.mukherjee@...ive.com>,
        Jude Onyenegecha <jude.onyenegecha@...ive.com>,
        Ben Dooks <ben.dooks@...ive.com>
Subject: [PATCH] swiotlb: ensure io_tlb_default_mem spinlock always initialised

If the io_tlb_default_mem is used by a device that then gets used
by the swiotlb code, the spinlock warning is triggered causing a
lot of stack-trace.

Fix this by making the structure's lock initialised at build time.

Avoids the following BUG trigger:

[    3.046401] BUG: spinlock bad magic on CPU#3, kworker/u8:0/7
[    3.046689]  lock: io_tlb_default_mem+0x30/0x60, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
[    3.047217] CPU: 3 PID: 7 Comm: kworker/u8:0 Not tainted 5.17.0-00056-g1e9bac738084-dirty #310
[    3.048363] Workqueue: events_unbound deferred_probe_work_func
[    3.048892] Call Trace:
[    3.049224] [<ffffffff800048aa>] dump_backtrace+0x1c/0x24
[    3.049576] [<ffffffff805c5f74>] show_stack+0x2c/0x38
[    3.049898] [<ffffffff805cade2>] dump_stack_lvl+0x40/0x58
[    3.050216] [<ffffffff805cae0e>] dump_stack+0x14/0x1c
[    3.050460] [<ffffffff805c69f6>] spin_dump+0x62/0x6e
[    3.050681] [<ffffffff8004e000>] do_raw_spin_lock+0xb0/0xd0
[    3.050934] [<ffffffff805d5b58>] _raw_spin_lock_irqsave+0x20/0x2c
[    3.051157] [<ffffffff80067e38>] swiotlb_tbl_map_single+0xce/0x3da
[    3.051372] [<ffffffff80068320>] swiotlb_map+0x3a/0x15c
[    3.051668] [<ffffffff80065a56>] dma_map_page_attrs+0x76/0x162
[    3.051975] [<ffffffff8031d542>] dw_pcie_host_init+0x326/0x3f2

Signed-off-by: Ben Dooks <ben.dooks@...ive.com>
---
 kernel/dma/swiotlb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index cb50f8d38360..a707a944c39a 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -65,7 +65,7 @@
 static bool swiotlb_force_bounce;
 static bool swiotlb_force_disable;
 
-struct io_tlb_mem io_tlb_default_mem;
+struct io_tlb_mem io_tlb_default_mem = { .lock = __SPIN_LOCK_UNLOCKED(io_tlb_default_mem.lock) } ;
 
 phys_addr_t swiotlb_unencrypted_base;
 
-- 
2.35.1