linux-ext4 - Re: [RFC v3 12/13] vfs: add debugfs support

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Date:	Wed, 10 Oct 2012 18:53:18 +0200
From:	David Sterba <dave@...os.cz>
To:	zwu.kernel@...il.com
Cc:	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linuxram@...ux.vnet.ibm.com, viro@...iv.linux.org.uk,
	david@...morbit.com, dave@...os.cz, tytso@....edu, cmm@...ibm.com,
	Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
Subject: Re: [RFC v3 12/13] vfs: add debugfs support

On Wed, Oct 10, 2012 at 06:07:34PM +0800, zwu.kernel@...il.com wrote:
> +static int hot_debugfs_log_init(struct debugfs_vol_data *data)
> +{
> +	int err = 0;
> +	struct lstring *debugfs_log = data->debugfs_log;
> +
> +	spin_lock(&data->log_lock);
> +	debugfs_log->str = vmalloc(INIT_LOG_ALLOC_SIZE);

vmalloc __might_sleep(), do the allocation outside of the lock and assign
the value inside. Also, you may use vzalloc and drop the following memset.

dmesg:

vfs: turning on hot data tracking
BUG: sleeping function called from invalid context at mm/slab.c:3220
in_atomic(): 1, irqs_disabled(): 0, pid: 3103, name: mc
1 lock held by mc/3103:
 #0:  (&(&inode_data->log_lock)->rlock){+.+.+.}, at: [<ffffffff8118c656>] __hot_debugfs_comm_read+0x216/0x280
Pid: 3103, comm: mc Tainted: G        W    3.6.0hottrack-default+ #208
Call Trace:
 [<ffffffff8108068c>] __might_sleep+0xfc/0x130
 [<ffffffff8114f7c1>] kmem_cache_alloc_trace+0xe1/0x270
 [<ffffffff81142005>] __get_vm_area_node+0x95/0x1a0
 [<ffffffff8108630f>] ? local_clock+0x6f/0x80
 [<ffffffff8118c660>] ? __hot_debugfs_comm_read+0x220/0x280
 [<ffffffff8114283d>] __vmalloc_node_range+0x6d/0x200
 [<ffffffff8118c660>] ? __hot_debugfs_comm_read+0x220/0x280
 [<ffffffff8118b810>] ? hot_debugfs_log+0xe0/0xe0
 [<ffffffff81142a05>] __vmalloc_node+0x35/0x40
 [<ffffffff8118c660>] ? __hot_debugfs_comm_read+0x220/0x280
 [<ffffffff81142bcc>] vmalloc+0x2c/0x30
 [<ffffffff8118c660>] __hot_debugfs_comm_read+0x220/0x280
 [<ffffffff8191fd58>] ? __do_page_fault+0x238/0x590
 [<ffffffff810ab825>] ? trace_hardirqs_on_caller+0x155/0x1d0
 [<ffffffff8138d01e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
 [<ffffffff8118c6d5>] __hot_debugfs_inode_read+0x15/0x20
 [<ffffffff8115a19b>] vfs_read+0xcb/0x190
 [<ffffffff8115a2c2>] sys_read+0x62/0xb0
 [<ffffffff8138d01e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
 [<ffffffff81924979>] system_call_fastpath+0x16/0x1b

> +	if (debugfs_log->str) {
> +		memset(debugfs_log->str, 0, INIT_LOG_ALLOC_SIZE);
> +		data->log_alloc_size = INIT_LOG_ALLOC_SIZE;
> +	} else {
> +		err = -ENOMEM;
> +	}
> +	spin_unlock(&data->log_lock);
> +
> +	return err;
> +}

I'm now playing with it, and haven't gone through the code yet,
david
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