[lustre-devel] [PATCH v2] lustre: mdc: fix possible deadlock in chlg_open()

NeilBrown neilb at suse.com
Mon Nov 5 19:11:54 PST 2018

On Mon, Nov 05 2018, quentin.bouget at cea.fr wrote:

> Le 04/11/2018 à 22:34, James Simmons a écrit :
>>> Lockdep reports a possible deadlock between chlg_open() and
>>> mdc_changelog_cdev_init()
>>> mdc_changelog_cdev_init() takes chlg_registered_dev_lock and then
>>> calls misc_register() which takes misc_mtx.
>>> chlg_open() is called while misc_mtx is held, and tries to take
>>> chlg_registered_dev_lock.
>>> If these two functions race, a deadlock can occur as each thread will
>>> hold one of the locks while trying to take the other.
>>> chlg_open() does not need to take a lock.  It only uses the
>>> lock to stablize a list while looking for the matching
>>> chlg_registered_dev, and this can be found directly by examining
>>> file->private_data.
>>> So remove chlg_obd_get(), and use file->private_data to find the
>>> obd_device.
>>> Also ensure the device is fully initialized before calling
>>> misc_register().  This means setting up some list linkage before the
>>> call, and tearing it down if there is an error.
>> I have been testing this but I'm no HSM expert. I pushed this patch
>> to OpenSFS branch as well.
>> https://jira.whamcloud.com/browse/LU-11617
>> https://review.whamcloud.com/#/c/33572/
>> Reviewed-by: James Simmons <jsimmons at infradead.org>
> Reviewed-by: Quentin Bouget <quentin.bouget at cea.fr>

Thanks to you both for the review.


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