From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Elder Subject: Re: [PATCH 1/2] rbd: move calls that may sleep out of spin lock range Date: Tue, 01 Oct 2013 16:17:25 -0500 Message-ID: <524B3BE5.5080406@linaro.org> References: <1379993136-29246-1-git-send-email-guangliang@unitedstack.com> <1380604559-5331-2-git-send-email-josh.durgin@inktank.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ie0-f173.google.com ([209.85.223.173]:49127 "EHLO mail-ie0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751454Ab3JAVRM (ORCPT ); Tue, 1 Oct 2013 17:17:12 -0400 Received: by mail-ie0-f173.google.com with SMTP id ar20so15087264iec.4 for ; Tue, 01 Oct 2013 14:17:11 -0700 (PDT) In-Reply-To: <1380604559-5331-2-git-send-email-josh.durgin@inktank.com> Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Josh Durgin , ceph-devel@vger.kernel.org On 10/01/2013 12:15 AM, Josh Durgin wrote: > get_user() and set_disk_ro() may allocate memory, leading to a > potential deadlock if theye are called while a spin lock is held. > > Move the acquisition and release of rbd_dev->lock from rbd_ioctl() > into rbd_ioctl_set_ro(), so it can occur between get_user() and > set_disk_ro(). This fix looks good. I have a couple small comments to consider. Reviewed-by: Alex Elder > Signed-off-by: Josh Durgin > --- > drivers/block/rbd.c | 36 +++++++++++++++++++++++------------- > 1 files changed, 23 insertions(+), 13 deletions(-) > > diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c > index 34bcdb7..b3b1b57 100644 > --- a/drivers/block/rbd.c > +++ b/drivers/block/rbd.c > @@ -510,23 +510,42 @@ static void rbd_release(struct gendisk *disk, fmode_t mode) > > static int rbd_ioctl_set_ro(struct rbd_device *rbd_dev, unsigned long arg) > { > + int ret = 0; > int val; > bool ro; > + bool ro_changed = false; > > + /* get_user() may sleep, so call it before taking rbd_dev->lock */ > if (get_user(val, (int __user *)(arg))) > return -EFAULT; > > + spin_lock_irq(&rbd_dev->lock); > + /* prevent others open this device */ > + if (rbd_dev->open_count > 1) { > + ret = -EBUSY; > + goto out; > + } I like to do as little as possible inside spinlock protection. > + > ro = val ? true : false; This assignment can be made outside the lock. > /* Snapshot doesn't allow to write*/ > - if (rbd_dev->spec->snap_id != CEPH_NOSNAP && !ro) > - return -EROFS; > + if (rbd_dev->spec->snap_id != CEPH_NOSNAP && !ro) { > + ret = -EROFS; > + goto out; > + } This check can be too. > > if (rbd_dev->mapping.read_only != ro) { > rbd_dev->mapping.read_only = ro; > - set_disk_ro(rbd_dev->disk, ro ? 1 : 0); > + ro_changed = true; > } > > - return 0; > +out: > + spin_unlock_irq(&rbd_dev->lock); > + /* set_disk_ro() may sleep, so call it after releasing rbd_dev->lock */ > + if (ret == 0 && ro_changed) > + set_disk_ro(rbd_dev->disk, ro ? 1 : 0); > + I like white space a lot, but this is one too many. > + > + return ret; > } > > static int rbd_ioctl(struct block_device *bdev, fmode_t mode, > @@ -535,13 +554,6 @@ static int rbd_ioctl(struct block_device *bdev, fmode_t mode, > struct rbd_device *rbd_dev = bdev->bd_disk->private_data; > int ret = 0; > > - spin_lock_irq(&rbd_dev->lock); > - /* prevent others open this device */ > - if (rbd_dev->open_count > 1) { > - ret = -EBUSY; > - goto out; > - } > - > switch (cmd) { > case BLKROSET: > ret = rbd_ioctl_set_ro(rbd_dev, arg); > @@ -550,8 +562,6 @@ static int rbd_ioctl(struct block_device *bdev, fmode_t mode, > ret = -ENOTTY; > } > > -out: > - spin_unlock_irq(&rbd_dev->lock); > return ret; > } > >