[lustre-devel] mdc_resource_inode_free()

[lustre-devel] mdc_resource_inode_free()

[Sudheendra Sampath]

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Hi,

I was trying to understand more about LDLM, specifically Lock Value Block
(LVB's) and stumbled upon the following code block :

static int mdc_resource_inode_free(struct ldlm_resource *res)
{
        if (res->lr_lvb_inode)
                res->lr_lvb_inode = NULL;

        return 0;
}

Shouldn't the pointer (lr_lvb_inode) be freed before assigning it to NULL
?

Just curious to know.
-- 
Regards

Sudheendra Sampath

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Re: [lustre-devel] mdc_resource_inode_free()

[Andreas Dilger]

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On Dec 22, 2020, at 13:25, Sudheendra Sampath <sudheendra.sampath@gmail.com<mailto:sudheendra.sampath@gmail.com>> wrote:

Hi,

I was trying to understand more about LDLM, specifically Lock Value Block (LVB's) and stumbled upon the following code block :

static int mdc_resource_inode_free(struct ldlm_resource *res)
{
        if (res->lr_lvb_inode)
                res->lr_lvb_inode = NULL;

        return 0;
}

Shouldn't the pointer (lr_lvb_inode) be freed before assigning it to NULL ?

Just curious to know.

The "lr_lvb_inode" pointer is a pointer to the VFS inode that is referencing a lock/resource:

int mdc_set_lock_data(struct obd_export *exp, const struct lustre_handle *lockh,
                      void *data, __u64 *bits)
{
        struct inode *new_inode = data;
        :
        lock->l_resource->lr_lvb_inode = new_inode;
}

The inode is allocated/freed separately by the VFS.  The lr_lvb_inode pointer is used to quickly find the VFS inode from a DLM resource, but does not take a reference on the inode itself.  Otherwise, the inode would always have an elevated reference count and would never be freed by the VFS.

Cheers, Andreas
--
Andreas Dilger
Principal Lustre Architect
Whamcloud







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