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Subject[PATCH] mailbox: PCC: Fix lockdep warning when request PCC channel
Date
This patch fixes the lockdep warning below

[ 7.229767] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
[ 7.229776] ------------[ cut here ]------------
[ 7.229787] WARNING: CPU: 1 PID: 1 at linux-next/kernel/locking/lockdep.c:2876 loc
kdep_trace_alloc+0xe0/0xf0
[ 7.229790] Modules linked in:
[ 7.229793]
[ 7.229798] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.8.0-11756-g86c5152 #46
...
[ 7.229900] Call trace:
[ 7.229903] Exception stack(0xffff8007da837890 to 0xffff8007da8379c0)
[ 7.229906] 7880: ffff8007da834000 0001000000000000
[ 7.229909] 78a0: ffff8007da837a70 ffff0000081111a0 00000000600000c5 000000000000003d
[ 7.229912] 78c0: 9374bc6a7f3c7832 0000000000381878 ffff000009db7ab8 000000000000002f
[ 7.229915] 78e0: ffff00000811aabc ffff000008be2548 ffff8007da837990 ffff00000811adf8
[ 7.229918] 7900: ffff8007da834000 00000000024080c0 00000000000000c0 ffff000009021000
[ 7.229921] 7920: 0000000000000000 0000000000000000 ffff000008c8f7c8 ffff8007da579810
[ 7.229923] 7940: 000000000000002f ffff8007da858000 0000000000000000 0000000000000001
[ 7.229926] 7960: 0000000000000001 0000000000000000 ffff00000811a468 0000000000000002
[ 7.229929] 7980: 656c62617369645f 0000000000038187 00000000000000ee ffff8007da837850
[ 7.229932] 79a0: ffff000009db50c0 ffff000009db569d 0000000000000006 ffff000089db568f
[ 7.229936] [<ffff0000081111a0>] lockdep_trace_alloc+0xe0/0xf0
[ 7.229940] [<ffff0000081f4950>] __kmalloc_track_caller+0x50/0x250
[ 7.229945] [<ffff00000857c088>] devres_alloc_node+0x28/0x60
[ 7.229949] [<ffff0000081220e0>] devm_request_threaded_irq+0x50/0xe0
[ 7.229955] [<ffff0000087e6220>] pcc_mbox_request_channel+0x110/0x170
[ 7.229960] [<ffff0000084b2660>] acpi_cppc_processor_probe+0x264/0x414
[ 7.229963] [<ffff0000084ae9f4>] __acpi_processor_start+0x28/0xa0
[ 7.229966] [<ffff0000084aeab0>] acpi_processor_start+0x44/0x54
[ 7.229970] [<ffff00000857897c>] driver_probe_device+0x1fc/0x2b0
[ 7.229974] [<ffff000008578ae4>] __driver_attach+0xb4/0xc0
[ 7.229977] [<ffff00000857683c>] bus_for_each_dev+0x5c/0xa0
[ 7.229980] [<ffff000008578110>] driver_attach+0x20/0x30
[ 7.229983] [<ffff000008577c20>] bus_add_driver+0x110/0x230
[ 7.229987] [<ffff000008579320>] driver_register+0x60/0x100
[ 7.229991] [<ffff000008d478b8>] acpi_processor_driver_init+0x2c/0xb0
[ 7.229996] [<ffff000008083168>] do_one_initcall+0x38/0x130
[ 7.230000] [<ffff000008d20d6c>] kernel_init_freeable+0x210/0x2b4
[ 7.230004] [<ffff000008945d90>] kernel_init+0x10/0x110
[ 7.230007] [<ffff000008082e80>] ret_from_fork+0x10/0x50

It's because the spinlock inside pcc_mbox_request_channel() is
kept too long. Adding a mutex to protect critical section of this
function. Beside of that, spinlock is still used to protect the
data of channel.

Signed-off-by: Hoan Tran <hotran@apm.com>
---
drivers/mailbox/pcc.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
index 08c87fa..b6cece0 100644
--- a/drivers/mailbox/pcc.c
+++ b/drivers/mailbox/pcc.c
@@ -81,6 +81,8 @@
static int *pcc_doorbell_irq;

static struct mbox_controller pcc_mbox_ctrl = {};
+static DEFINE_MUTEX(pcc_con_mutex);
+
/**
* get_pcc_channel - Given a PCC subspace idx, get
* the respective mbox_channel.
@@ -243,6 +245,7 @@ struct mbox_chan *pcc_mbox_request_channel(struct mbox_client *cl,
struct mbox_chan *chan;
unsigned long flags;

+ mutex_lock(&pcc_con_mutex);
/*
* Each PCC Subspace is a Mailbox Channel.
* The PCC Clients get their PCC Subspace ID
@@ -254,6 +257,7 @@ struct mbox_chan *pcc_mbox_request_channel(struct mbox_client *cl,

if (IS_ERR(chan) || chan->cl) {
dev_err(dev, "Channel not found for idx: %d\n", subspace_id);
+ mutex_unlock(&pcc_con_mutex);
return ERR_PTR(-EBUSY);
}

@@ -267,6 +271,8 @@ struct mbox_chan *pcc_mbox_request_channel(struct mbox_client *cl,
if (chan->txdone_method == TXDONE_BY_POLL && cl->knows_txdone)
chan->txdone_method |= TXDONE_BY_ACK;

+ spin_unlock_irqrestore(&chan->lock, flags);
+
if (pcc_doorbell_irq[subspace_id] > 0) {
int rc;

@@ -279,7 +285,7 @@ struct mbox_chan *pcc_mbox_request_channel(struct mbox_client *cl,
}
}

- spin_unlock_irqrestore(&chan->lock, flags);
+ mutex_unlock(&pcc_con_mutex);

return chan;
}
--
1.9.1
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