1111#include <linux/printk.h>
1212#include <linux/slab.h>
1313#include <linux/sysfs.h>
14+ #include <linux/workqueue.h>
1415
1516#include "dma-buf-sysfs-stats.h"
1617
@@ -135,10 +136,51 @@ void dma_buf_uninit_sysfs_statistics(void)
135136 kset_unregister (dma_buf_stats_kset );
136137}
137138
139+ static void sysfs_add_workfn (struct work_struct * work )
140+ {
141+ /* The ABI would have to change for this to be false, but let's be paranoid. */
142+ _Static_assert (sizeof (struct kobject ) >= sizeof (struct work_struct ),
143+ "kobject is smaller than work_struct" );
144+
145+ struct dma_buf_sysfs_entry * sysfs_entry =
146+ container_of ((struct kobject * )work , struct dma_buf_sysfs_entry , kobj );
147+ struct dma_buf * dmabuf = sysfs_entry -> dmabuf ;
148+
149+ /*
150+ * A dmabuf is ref-counted via its file member. If this handler holds the only
151+ * reference to the dmabuf, there is no need for sysfs kobject creation. This is an
152+ * optimization and a race; when the reference count drops to 1 immediately after
153+ * this check it is not harmful as the sysfs entry will still get cleaned up in
154+ * dma_buf_stats_teardown, which won't get called until the final dmabuf reference
155+ * is released, and that can't happen until the end of this function.
156+ */
157+ if (file_count (dmabuf -> file ) > 1 ) {
158+ /*
159+ * kobject_init_and_add expects kobject to be zero-filled, but we have populated it
160+ * to trigger this work function.
161+ */
162+ memset (& dmabuf -> sysfs_entry -> kobj , 0 , sizeof (dmabuf -> sysfs_entry -> kobj ));
163+ dmabuf -> sysfs_entry -> kobj .kset = dma_buf_per_buffer_stats_kset ;
164+ if (kobject_init_and_add (& dmabuf -> sysfs_entry -> kobj , & dma_buf_ktype , NULL ,
165+ "%lu" , file_inode (dmabuf -> file )-> i_ino )) {
166+ kobject_put (& dmabuf -> sysfs_entry -> kobj );
167+ dmabuf -> sysfs_entry = NULL ;
168+ }
169+ } else {
170+ /*
171+ * Free the sysfs_entry and reset the pointer so dma_buf_stats_teardown doesn't
172+ * attempt to operate on it.
173+ */
174+ kfree (dmabuf -> sysfs_entry );
175+ dmabuf -> sysfs_entry = NULL ;
176+ }
177+ dma_buf_put (dmabuf );
178+ }
179+
138180int dma_buf_stats_setup (struct dma_buf * dmabuf )
139181{
140182 struct dma_buf_sysfs_entry * sysfs_entry ;
141- int ret ;
183+ struct work_struct * work ;
142184
143185 if (!dmabuf || !dmabuf -> file )
144186 return - EINVAL ;
@@ -148,25 +190,21 @@ int dma_buf_stats_setup(struct dma_buf *dmabuf)
148190 return - EINVAL ;
149191 }
150192
151- sysfs_entry = kzalloc (sizeof (struct dma_buf_sysfs_entry ), GFP_KERNEL );
193+ sysfs_entry = kmalloc (sizeof (struct dma_buf_sysfs_entry ), GFP_KERNEL );
152194 if (!sysfs_entry )
153195 return - ENOMEM ;
154196
155- sysfs_entry -> kobj .kset = dma_buf_per_buffer_stats_kset ;
156197 sysfs_entry -> dmabuf = dmabuf ;
157-
158198 dmabuf -> sysfs_entry = sysfs_entry ;
159199
160- /* create the directory for buffer stats */
161- ret = kobject_init_and_add (& sysfs_entry -> kobj , & dma_buf_ktype , NULL ,
162- "%lu" , file_inode (dmabuf -> file )-> i_ino );
163- if (ret )
164- goto err_sysfs_dmabuf ;
200+ /*
201+ * The use of kobj as a work_struct is an ugly hack
202+ * to avoid an ABI break in this frozen kernel.
203+ */
204+ work = (struct work_struct * )& dmabuf -> sysfs_entry -> kobj ;
205+ INIT_WORK (work , sysfs_add_workfn );
206+ get_dma_buf (dmabuf ); /* This reference will be dropped in sysfs_add_workfn. */
207+ schedule_work (work );
165208
166209 return 0 ;
167-
168- err_sysfs_dmabuf :
169- kobject_put (& sysfs_entry -> kobj );
170- dmabuf -> sysfs_entry = NULL ;
171- return ret ;
172210}
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