Re: [PATCH] crypto/ccp: don't disable interrupts while setting up debugfs

[Hook, Gary]

On 2/23/2018 5:33 PM, Sebastian Andrzej Siewior wrote:
I don't why we need take a single write lock and disable interrupts
while setting up debugfs. This is what what happens when we try anyway:

There is more than one CCP on some processors. The lock is intended to
serialize attempts to initialize the new directory, but a R/W lock isn't 
required.

My testing on  an EPYC (8 CCPs) didn't expose this problem. May I ask 
what hardware you used here?

|ccp 0000:03:00.2: enabling device (0000 -> 0002)
|BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:69
|in_atomic(): 1, irqs_disabled(): 1, pid: 3, name: kworker/0:0
|irq event stamp: 17150
|hardirqs last  enabled at (17149): [<0000000097a18c49>] 
restore_regs_and_return_to_kernel+0x0/0x23
|hardirqs last disabled at (17150): [<000000000773b3a9>] 
_raw_write_lock_irqsave+0x1b/0x50
|softirqs last  enabled at (17148): [<0000000064d56155>] 
__do_softirq+0x3b8/0x4c1
|softirqs last disabled at (17125): [<0000000092633c18>] irq_exit+0xb1/0xc0
|CPU: 0 PID: 3 Comm: kworker/0:0 Not tainted 4.16.0-rc2+ #30
|Workqueue: events work_for_cpu_fn
|Call Trace:
| dump_stack+0x7d/0xb6
| ___might_sleep+0x1eb/0x250
| down_write+0x17/0x60
| start_creating+0x4c/0xe0
| debugfs_create_dir+0x9/0x100
| ccp5_debugfs_setup+0x191/0x1b0
| ccp5_init+0x8a7/0x8c0
| ccp_dev_init+0xb8/0xe0
| sp_init+0x6c/0x90
| sp_pci_probe+0x26e/0x590
| local_pci_probe+0x3f/0x90
| work_for_cpu_fn+0x11/0x20
| process_one_work+0x1ff/0x650
| worker_thread+0x1d4/0x3a0
| kthread+0xfe/0x130
| ret_from_fork+0x27/0x50

If any locking is required, a simple mutex will do it.

Cc: Gary R Hook <gary.h...@amd.com>
Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
---
  drivers/crypto/ccp/ccp-debugfs.c | 7 +++----
  1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/crypto/ccp/ccp-debugfs.c b/drivers/crypto/ccp/ccp-debugfs.c
index 59d4ca4e72d8..1a734bd2070a 100644
--- a/drivers/crypto/ccp/ccp-debugfs.c
+++ b/drivers/crypto/ccp/ccp-debugfs.c
@@ -278,7 +278,7 @@ static const struct file_operations ccp_debugfs_stats_ops = 
{
  };
  
  static struct dentry *ccp_debugfs_dir;
-static DEFINE_RWLOCK(ccp_debugfs_lock);
+static DEFINE_MUTEX(ccp_debugfs_lock);
  
  #define	MAX_NAME_LEN	20
  
@@ -290,16 +290,15 @@ void ccp5_debugfs_setup(struct ccp_device *ccp)
        struct dentry *debugfs_stats;
        struct dentry *debugfs_q_instance;
        struct dentry *debugfs_q_stats;
-       unsigned long flags;
        int i;
  
  	if (!debugfs_initialized())
                return;
  
-	write_lock_irqsave(&ccp_debugfs_lock, flags);
+       mutex_lock(&ccp_debugfs_lock);
        if (!ccp_debugfs_dir)
                ccp_debugfs_dir = debugfs_create_dir(KBUILD_MODNAME, NULL);
-       write_unlock_irqrestore(&ccp_debugfs_lock, flags);
+       mutex_unlock(&ccp_debugfs_lock);
        if (!ccp_debugfs_dir)
                return;