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    Subject[PATCH][-mm] reclassify sg_sysfs_class for lockdep
    As register sg_interface, the sg_add will be called, which then will
    add device to sg_sysfs_class. This will cause lockdep warning,
    please see following email

    In this case the locks are from diffrent classi, one is sdev_class,
    another is sg_sysfs_class

    Here reclassify the sg_sysfs_class for lockdep

    Date: Wed, 14 May 2008 08:56:39 -0700
    From: Greg KH <greg@kroah.com>
    To: Andrew Morton <akpm@linux-foundation.org>,
    Dave Young <hidave.darkstar@gmail.com>
    Cc: linux-scsi@vger.kernel.org, Kay Sievers <kay.sievers@vrfy.org>
    Subject: Re: lockdep whine in 2.6.26-rc2-mm1
    Message-ID: <20080514155639.GB28594@kroah.com>
    References: <20080514000933.56adc131.akpm@linux-foundation.org>
    MIME-Version: 1.0
    Content-Type: text/plain; charset=us-ascii
    Content-Disposition: inline
    In-Reply-To: <20080514000933.56adc131.akpm@linux-foundation.org>
    User-Agent: Mutt/1.5.16 (2007-06-09)


    On Wed, May 14, 2008 at 12:09:33AM -0700, Andrew Morton wrote:
    >
    > =============================================
    > [ INFO: possible recursive locking detected ]
    > 2.6.26-rc2-mm1 #15
    > ---------------------------------------------
    > modprobe/942 is trying to acquire lock:
    > (&cls->mutex){--..}, at: [<ffffffff811b431e>] device_add+0x43d/0x57a
    >
    > but task is already holding lock:
    > (&cls->mutex){--..}, at: [<ffffffff811b6787>] class_interface_register+0x48/0xbd
    >
    > other info that might help us debug this:
    > 1 lock held by modprobe/942:
    > #0: (&cls->mutex){--..}, at: [<ffffffff811b6787>] class_interface_register+0x48/0xbd
    >
    > stack backtrace:
    > Pid: 942, comm: modprobe Not tainted 2.6.26-rc2-mm1 #15
    >
    > Call Trace:
    > [<ffffffff81056be1>] __lock_acquire+0x90d/0xc50
    > [<ffffffff8100c50f>] ? restore_args+0x0/0x30
    > [<ffffffff811b431e>] ? device_add+0x43d/0x57a
    > [<ffffffff81057276>] lock_acquire+0x91/0xb7
    > [<ffffffff811b431e>] ? device_add+0x43d/0x57a
    > [<ffffffff812b23ab>] mutex_lock_nested+0xf2/0x278
    > [<ffffffff811b431e>] ? device_add+0x43d/0x57a
    > [<ffffffff812b3acd>] ? _spin_unlock+0x23/0x28
    > [<ffffffff811b431e>] device_add+0x43d/0x57a
    > [<ffffffff811b4471>] device_register+0x16/0x1b
    > [<ffffffff811b4555>] device_create+0xdf/0x112
    > [<ffffffff81055fdc>] ? trace_hardirqs_on+0xd/0xf
    > [<ffffffff81055fdc>] ? trace_hardirqs_on+0xd/0xf
    > [<ffffffff812b1fe1>] ? mutex_unlock+0x9/0xb
    > [<ffffffff811b79b7>] ? kobj_map+0x113/0x124
    > [<ffffffff810ac0f5>] ? exact_lock+0x0/0x14
    > [<ffffffff810abd09>] ? exact_match+0x0/0x9
    > [<ffffffffa00ec448>] :sg:sg_add+0x2a3/0x3bd
    > [<ffffffff811b67b6>] class_interface_register+0x77/0xbd
    > [<ffffffffa005d869>] :scsi_mod:scsi_register_interface+0x11/0x13
    > [<ffffffffa00d50a3>] :sg:init_sg+0xa3/0x155
    > [<ffffffff8105ea8f>] sys_init_module+0x1823/0x197a
    > [<ffffffff810c45bc>] ? seq_release+0x0/0x56
    > [<ffffffff8100bebb>] system_call_after_swapgs+0x7b/0x80

    Signed-off-by: Dave Young <hidave.darkstar@gmail.com>

    ---
    drivers/scsi/sg.c | 6 ++++++
    1 file changed, 6 insertions(+)

    diff -upr linux/drivers/scsi/sg.c linux.new/drivers/scsi/sg.c
    --- linux/drivers/scsi/sg.c 2008-05-27 17:09:42.000000000 +0800
    +++ linux.new/drivers/scsi/sg.c 2008-05-27 17:09:51.000000000 +0800
    @@ -49,6 +49,7 @@ static int sg_version_num = 30534; /* 2
    #include <linux/delay.h>
    #include <linux/scatterlist.h>
    #include <linux/blktrace_api.h>
    +#include <linux/lockdep.h>

    #include "scsi.h"
    #include <scsi/scsi_dbg.h>
    @@ -67,6 +68,8 @@ static int sg_proc_init(void);
    static void sg_proc_cleanup(void);
    #endif

    +static struct lock_class_key sg_class_key;
    +
    #define SG_ALLOW_DIO_DEF 0
    #define SG_ALLOW_DIO_CODE /* compile out by commenting this define */

    @@ -1579,6 +1582,9 @@ init_sg(void)
    rc = PTR_ERR(sg_sysfs_class);
    goto err_out;
    }
    +
    + lockdep_set_class_and_name(&sg_sysfs_class->mutex, &sg_class_key,
    + sg_sysfs_class->name);
    sg_sysfs_valid = 1;
    rc = scsi_register_interface(&sg_interface);
    if (0 == rc) {

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