locking in fs/9p ->readdir()

... is really excessive. First of all, ->readdir() is serialized by file->f_path.dentry->d_inode->i_mutex; playing with file->f_path.dentry->d_lock is not buying you anything. Moreover, rdir->mutex is pointless for exactly the same reason - you'll never see contention on it. While we are at it, there's no point in having rdir->buf a pointer - you have it point just past the end of rdir, so it might as well be a flex array (and no, it's not a gccism). Absolutely untested patch follows: Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

locking in fs/9p ->readdir()
... is really excessive. First of all, ->readdir() is serialized by file->f_path.dentry->d_inode->i_mutex; playing with file->f_path.dentry->d_lock is not buying you anything. Moreover, rdir->mutex is pointless for exactly the same reason - you'll never see contention on it. While we are at it, there's no point in having rdir->buf a pointer - you have it point just past the end of rdir, so it might as well be a flex array (and no, it's not a gccism). Absolutely untested patch follows: Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
Al Viro · Eric Van Hensbergen
1 parent 836dc9e3fb
Showing 1 changed file with 23 additions and 69 deletions Side-by-side Diff
fs/9p/vfs_dir.c
@@ -52,10 +52,9 @@
  */
  
 struct p9_rdir {
-	struct mutex mutex;
 	int head;
 	int tail;
-	uint8_t *buf;
+	uint8_t buf[];
 };
  
 /**
  
@@ -93,33 +92,12 @@
  *
  */
  
-static int v9fs_alloc_rdir_buf(struct file *filp, int buflen)
+static struct p9_rdir *v9fs_alloc_rdir_buf(struct file *filp, int buflen)
 {
-	struct p9_rdir *rdir;
-	struct p9_fid *fid;
-	int err = 0;
-
-	fid = filp->private_data;
-	if (!fid->rdir) {
-		rdir = kmalloc(sizeof(struct p9_rdir) + buflen, GFP_KERNEL);
-
-		if (rdir == NULL) {
-			err = -ENOMEM;
-			goto exit;
-		}
-		spin_lock(&filp->f_dentry->d_lock);
-		if (!fid->rdir) {
-			rdir->buf = (uint8_t *)rdir + sizeof(struct p9_rdir);
-			mutex_init(&rdir->mutex);
-			rdir->head = rdir->tail = 0;
-			fid->rdir = (void *) rdir;
-			rdir = NULL;
-		}
-		spin_unlock(&filp->f_dentry->d_lock);
-		kfree(rdir);
-	}
-exit:
-	return err;
+	struct p9_fid *fid = filp->private_data;
+	if (!fid->rdir)
+		fid->rdir = kzalloc(sizeof(struct p9_rdir) + buflen, GFP_KERNEL);
+	return fid->rdir;
 }
  
 /**
  
  
@@ -145,20 +123,16 @@
  
 	buflen = fid->clnt->msize - P9_IOHDRSZ;
  
-	err = v9fs_alloc_rdir_buf(filp, buflen);
-	if (err)
-		goto exit;
-	rdir = (struct p9_rdir *) fid->rdir;
+	rdir = v9fs_alloc_rdir_buf(filp, buflen);
+	if (!rdir)
+		return -ENOMEM;
  
-	err = mutex_lock_interruptible(&rdir->mutex);
-	if (err)
-		return err;
-	while (err == 0) {
+	while (1) {
 		if (rdir->tail == rdir->head) {
 			err = v9fs_file_readn(filp, rdir->buf, NULL,
 							buflen, filp->f_pos);
 			if (err <= 0)
-				goto unlock_and_exit;
+				return err;
  
 			rdir->head = 0;
 			rdir->tail = err;
  
@@ -169,9 +143,8 @@
 					  rdir->tail - rdir->head, &st);
 			if (err) {
 				p9_debug(P9_DEBUG_VFS, "returned %d\n", err);
-				err = -EIO;
 				p9stat_free(&st);
-				goto unlock_and_exit;
+				return -EIO;
 			}
 			reclen = st.size+2;
  
  
@@ -180,19 +153,13 @@
  
 			p9stat_free(&st);
  
-			if (over) {
-				err = 0;
-				goto unlock_and_exit;
-			}
+			if (over)
+				return 0;
+
 			rdir->head += reclen;
 			filp->f_pos += reclen;
 		}
 	}
-
-unlock_and_exit:
-	mutex_unlock(&rdir->mutex);
-exit:
-	return err;
 }
  
 /**
  
  
@@ -218,21 +185,16 @@
  
 	buflen = fid->clnt->msize - P9_READDIRHDRSZ;
  
-	err = v9fs_alloc_rdir_buf(filp, buflen);
-	if (err)
-		goto exit;
-	rdir = (struct p9_rdir *) fid->rdir;
+	rdir = v9fs_alloc_rdir_buf(filp, buflen);
+	if (!rdir)
+		return -ENOMEM;
  
-	err = mutex_lock_interruptible(&rdir->mutex);
-	if (err)
-		return err;
-
-	while (err == 0) {
+	while (1) {
 		if (rdir->tail == rdir->head) {
 			err = p9_client_readdir(fid, rdir->buf, buflen,
 						filp->f_pos);
 			if (err <= 0)
-				goto unlock_and_exit;
+				return err;
  
 			rdir->head = 0;
 			rdir->tail = err;
@@ -245,8 +207,7 @@
 					    &curdirent);
 			if (err < 0) {
 				p9_debug(P9_DEBUG_VFS, "returned %d\n", err);
-				err = -EIO;
-				goto unlock_and_exit;
+				return -EIO;
 			}
  
 			/* d_off in dirent structure tracks the offset into
  
@@ -261,20 +222,13 @@
 					curdirent.d_type);
 			oldoffset = curdirent.d_off;
  
-			if (over) {
-				err = 0;
-				goto unlock_and_exit;
-			}
+			if (over)
+				return 0;
  
 			filp->f_pos = curdirent.d_off;
 			rdir->head += err;
 		}
 	}
-
-unlock_and_exit:
-	mutex_unlock(&rdir->mutex);
-exit:
-	return err;
 }
...	...	@@ -52,10 +52,9 @@
52	52	*/
53	53
54	54	struct p9_rdir {
55		- struct mutex mutex;
56	55	int head;
57	56	int tail;
58		- uint8_t *buf;
	57	+ uint8_t buf[];
59	58	};
60	59
61	60	/**
62	61
...	...	@@ -93,33 +92,12 @@
93	92	*
94	93	*/
95	94
96		-static int v9fs_alloc_rdir_buf(struct file *filp, int buflen)
	95	+static struct p9_rdir v9fs_alloc_rdir_buf(struct file filp, int buflen)
97	96	{
98		- struct p9_rdir *rdir;
99		- struct p9_fid *fid;
100		- int err = 0;
101		-
102		- fid = filp->private_data;
103		- if (!fid->rdir) {
104		- rdir = kmalloc(sizeof(struct p9_rdir) + buflen, GFP_KERNEL);
105		-
106		- if (rdir == NULL) {
107		- err = -ENOMEM;
108		- goto exit;
109		- }
110		- spin_lock(&filp->f_dentry->d_lock);
111		- if (!fid->rdir) {
112		- rdir->buf = (uint8_t *)rdir + sizeof(struct p9_rdir);
113		- mutex_init(&rdir->mutex);
114		- rdir->head = rdir->tail = 0;
115		- fid->rdir = (void *) rdir;
116		- rdir = NULL;
117		- }
118		- spin_unlock(&filp->f_dentry->d_lock);
119		- kfree(rdir);
120		- }
121		-exit:
122		- return err;
	97	+ struct p9_fid *fid = filp->private_data;
	98	+ if (!fid->rdir)
	99	+ fid->rdir = kzalloc(sizeof(struct p9_rdir) + buflen, GFP_KERNEL);
	100	+ return fid->rdir;
123	101	}
124	102
125	103	/**
126	104
127	105
...	...	@@ -145,20 +123,16 @@
145	123
146	124	buflen = fid->clnt->msize - P9_IOHDRSZ;
147	125
148		- err = v9fs_alloc_rdir_buf(filp, buflen);
149		- if (err)
150		- goto exit;
151		- rdir = (struct p9_rdir *) fid->rdir;
	126	+ rdir = v9fs_alloc_rdir_buf(filp, buflen);
	127	+ if (!rdir)
	128	+ return -ENOMEM;
152	129
153		- err = mutex_lock_interruptible(&rdir->mutex);
154		- if (err)
155		- return err;
156		- while (err == 0) {
	130	+ while (1) {
157	131	if (rdir->tail == rdir->head) {
158	132	err = v9fs_file_readn(filp, rdir->buf, NULL,
159	133	buflen, filp->f_pos);
160	134	if (err <= 0)
161		- goto unlock_and_exit;
	135	+ return err;
162	136
163	137	rdir->head = 0;
164	138	rdir->tail = err;
165	139
...	...	@@ -169,9 +143,8 @@
169	143	rdir->tail - rdir->head, &st);
170	144	if (err) {
171	145	p9_debug(P9_DEBUG_VFS, "returned %d\n", err);
172		- err = -EIO;
173	146	p9stat_free(&st);
174		- goto unlock_and_exit;
	147	+ return -EIO;
175	148	}
176	149	reclen = st.size+2;
177	150
178	151
...	...	@@ -180,19 +153,13 @@
180	153
181	154	p9stat_free(&st);
182	155
183		- if (over) {
184		- err = 0;
185		- goto unlock_and_exit;
186		- }
	156	+ if (over)
	157	+ return 0;
	158	+
187	159	rdir->head += reclen;
188	160	filp->f_pos += reclen;
189	161	}
190	162	}
191		-
192		-unlock_and_exit:
193		- mutex_unlock(&rdir->mutex);
194		-exit:
195		- return err;
196	163	}
197	164
198	165	/**
199	166
200	167
...	...	@@ -218,21 +185,16 @@
218	185
219	186	buflen = fid->clnt->msize - P9_READDIRHDRSZ;
220	187
221		- err = v9fs_alloc_rdir_buf(filp, buflen);
222		- if (err)
223		- goto exit;
224		- rdir = (struct p9_rdir *) fid->rdir;
	188	+ rdir = v9fs_alloc_rdir_buf(filp, buflen);
	189	+ if (!rdir)
	190	+ return -ENOMEM;
225	191
226		- err = mutex_lock_interruptible(&rdir->mutex);
227		- if (err)
228		- return err;
229		-
230		- while (err == 0) {
	192	+ while (1) {
231	193	if (rdir->tail == rdir->head) {
232	194	err = p9_client_readdir(fid, rdir->buf, buflen,
233	195	filp->f_pos);
234	196	if (err <= 0)
235		- goto unlock_and_exit;
	197	+ return err;
236	198
237	199	rdir->head = 0;
238	200	rdir->tail = err;
...	...	@@ -245,8 +207,7 @@
245	207	&curdirent);
246	208	if (err < 0) {
247	209	p9_debug(P9_DEBUG_VFS, "returned %d\n", err);
248		- err = -EIO;
249		- goto unlock_and_exit;
	210	+ return -EIO;
250	211	}
251	212
252	213	/* d_off in dirent structure tracks the offset into
253	214
...	...	@@ -261,20 +222,13 @@
261	222	curdirent.d_type);
262	223	oldoffset = curdirent.d_off;
263	224
264		- if (over) {
265		- err = 0;
266		- goto unlock_and_exit;
267		- }
	225	+ if (over)
	226	+ return 0;
268	227
269	228	filp->f_pos = curdirent.d_off;
270	229	rdir->head += err;
271	230	}
272	231	}
273		-
274		-unlock_and_exit:
275		- mutex_unlock(&rdir->mutex);
276		-exit:
277		- return err;
278	232	}
279	233
280	234