From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Yan Subject: [PATCH] scsi: fix race condition when removing target Date: Wed, 29 Nov 2017 11:05:56 +0800 Message-ID: <20171129030556.47833-1-yanaijie@huawei.com> Mime-Version: 1.0 Content-Type: text/plain Return-path: Received: from szxga05-in.huawei.com ([45.249.212.191]:11035 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752720AbdK2DAV (ORCPT ); Tue, 28 Nov 2017 22:00:21 -0500 Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: martin.petersen@oracle.com, jejb@linux.vnet.ibm.com Cc: linux-scsi@vger.kernel.org, Jason Yan , Hannes Reinecke , Christoph Hellwig , Johannes Thumshirn , Zhaohongjiang , Miao Xie In commit fbce4d97fd43 ("scsi: fixup kernel warning during rmmod()"), we removed scsi_device_get() and directly called get_device() to increase the refcount of the device. But actullay scsi_device_get() will fail in three cases: 1. the scsi device is in SDEV_DEL or SDEV_CANCEL state 2. get_device() fail 3. the module is not alive The intended purpose was to remove the check of the module alive. Unfortunately the check of the device state was droped too. And this introduced a race condition like this: CPU0 CPU1 __scsi_remove_target() ->iterate shost->__devices ->scsi_remove_device() ->put_device() someone still hold a refcount sd_release() ->scsi_disk_put() ->put_device() last put and trigger the device release ->goto restart ->iterate shost->__devices and got the same device ->get_device() while refcount is 0 ->scsi_remove_device() ->put_device() refcount decreased to 0 again ->scsi_device_dev_release() ->scsi_device_dev_release_usercontext() ->scsi_device_dev_release() ->scsi_device_dev_release_usercontext() The same scsi device will be found agian because it is in the shost->__devices list until scsi_device_dev_release_usercontext() called, although the device state was set to SDEV_DEL after the first scsi_remove_device(). Finally we got a oops in scsi_device_dev_release_usercontext() when the second time be called. Call trace: [] scsi_device_dev_release_usercontext+0x7c/0x1c0 [] execute_in_process_context+0x70/0x80 [] scsi_device_dev_release+0x28/0x38 [] device_release+0x3c/0xa0 [] kobject_put+0x80/0xf0 [] put_device+0x24/0x30 [] scsi_device_put+0x30/0x40 [] scsi_disk_put+0x44/0x60 [] sd_release+0x50/0x80 [] __blkdev_put+0x21c/0x230 [] blkdev_put+0x54/0x118 [] blkdev_close+0x2c/0x40 [] __fput+0x94/0x1d8 [] ____fput+0x20/0x30 [] task_work_run+0x9c/0xb8 [] do_exit+0x2b4/0x9f8 [] do_group_exit+0x3c/0xa0 [] __wake_up_parent+0x0/0x40 And sometimes in __scsi_remove_target() it will loop for a long time removing the same device if someone else holding a refcount until the last refcount is released. Notice that if CONFIG_REFCOUNT_FULL is open this race won't be triggered because the full refcount implement will prevent the refcount increase when it is 0. Fix this by checking the sdev_state again like we did before in scsi_device_get(). Then when iterating shost again we will skip the device deleted because scsi_remove_device() will set the device state to SDEV_CANCEL or SDEV_DEL. Fixes: fbce4d97fd43 ("scsi: fixup kernel warning during rmmod()") Signed-off-by: Jason Yan CC: Hannes Reinecke CC: Christoph Hellwig CC: Johannes Thumshirn CC: Zhaohongjiang CC: Miao Xie --- drivers/scsi/scsi_sysfs.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c index 50e7d7e..d398894 100644 --- a/drivers/scsi/scsi_sysfs.c +++ b/drivers/scsi/scsi_sysfs.c @@ -1398,6 +1398,15 @@ void scsi_remove_device(struct scsi_device *sdev) } EXPORT_SYMBOL(scsi_remove_device); +static int scsi_device_get_not_deleted(struct scsi_device *sdev) +{ + if (sdev->sdev_state == SDEV_DEL || sdev->sdev_state == SDEV_CANCEL) + return -ENXIO; + if (!get_device(&sdev->sdev_gendev)) + return -ENXIO; + return 0; +} + static void __scsi_remove_target(struct scsi_target *starget) { struct Scsi_Host *shost = dev_to_shost(starget->dev.parent); @@ -1415,7 +1424,7 @@ static void __scsi_remove_target(struct scsi_target *starget) */ if (sdev->channel != starget->channel || sdev->id != starget->id || - !get_device(&sdev->sdev_gendev)) + scsi_device_get_not_deleted(sdev)) continue; spin_unlock_irqrestore(shost->host_lock, flags); scsi_remove_device(sdev); -- 2.9.5