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authorNeilBrown <neilb@suse.de>2014-10-13 16:41:28 +1100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-11-07 10:53:25 -0800
commit2b75869bba676c248d8d25ae6d2bd9221dfffdb6 (patch)
treebcbf58a3e4da882e9cc4dda7da4b65f18a01fa81
parent0936896056365349afa867c16e9f9100a6707cbf (diff)
sysfs/kernfs: allow attributes to request write buffer be pre-allocated.
md/raid allows metadata management to be performed in user-space. A various times, particularly on device failure, the metadata needs to be updated before further writes can be permitted. This means that the user-space program which updates metadata much not block on writeout, and so must not allocate memory. mlockall(MCL_CURRENT|MCL_FUTURE) and pre-allocation can avoid all memory allocation issues for user-memory, but that does not help kernel memory. Several kernel objects can be pre-allocated. e.g. files opened before any writes to the array are permitted. However some kernel allocation happens in places that cannot be pre-allocated. In particular, writes to sysfs files (to tell md that it can now allow writes to the array) allocate a buffer using GFP_KERNEL. This patch allows attributes to be marked as "PREALLOC". In that case the maximal buffer is allocated when the file is opened, and then used on each write instead of allocating a new buffer. As the same buffer is now shared for all writes on the same file description, the mutex is extended to cover full use of the buffer including the copy_from_user(). The new __ATTR_PREALLOC() 'or's a new flag in to the 'mode', which is inspected by sysfs_add_file_mode_ns() to determine if the file should be marked as requiring prealloc. Despite the comment, we *do* use ->seq_show together with ->prealloc in this patch. The next patch fixes that. Signed-off-by: NeilBrown <neilb@suse.de> Reviewed-by: Tejun Heo <tj@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--fs/kernfs/file.c45
-rw-r--r--fs/sysfs/file.c31
-rw-r--r--include/linux/kernfs.h8
-rw-r--r--include/linux/sysfs.h9
4 files changed, 71 insertions, 22 deletions
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 4429d6d9217f..70186e2e692a 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -106,7 +106,7 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
const struct kernfs_ops *ops;
/*
- * @of->mutex nests outside active ref and is just to ensure that
+ * @of->mutex nests outside active ref and is primarily to ensure that
* the ops aren't called concurrently for the same open file.
*/
mutex_lock(&of->mutex);
@@ -194,7 +194,7 @@ static ssize_t kernfs_file_direct_read(struct kernfs_open_file *of,
return -ENOMEM;
/*
- * @of->mutex nests outside active ref and is just to ensure that
+ * @of->mutex nests outside active ref and is primarily to ensure that
* the ops aren't called concurrently for the same open file.
*/
mutex_lock(&of->mutex);
@@ -278,19 +278,16 @@ static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
len = min_t(size_t, count, PAGE_SIZE);
}
- buf = kmalloc(len + 1, GFP_KERNEL);
+ buf = of->prealloc_buf;
+ if (!buf)
+ buf = kmalloc(len + 1, GFP_KERNEL);
if (!buf)
return -ENOMEM;
- if (copy_from_user(buf, user_buf, len)) {
- len = -EFAULT;
- goto out_free;
- }
- buf[len] = '\0'; /* guarantee string termination */
-
/*
- * @of->mutex nests outside active ref and is just to ensure that
- * the ops aren't called concurrently for the same open file.
+ * @of->mutex nests outside active ref and is used both to ensure that
+ * the ops aren't called concurrently for the same open file, and
+ * to provide exclusive access to ->prealloc_buf (when that exists).
*/
mutex_lock(&of->mutex);
if (!kernfs_get_active(of->kn)) {
@@ -299,19 +296,27 @@ static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
goto out_free;
}
+ if (copy_from_user(buf, user_buf, len)) {
+ len = -EFAULT;
+ goto out_unlock;
+ }
+ buf[len] = '\0'; /* guarantee string termination */
+
ops = kernfs_ops(of->kn);
if (ops->write)
len = ops->write(of, buf, len, *ppos);
else
len = -EINVAL;
- kernfs_put_active(of->kn);
- mutex_unlock(&of->mutex);
-
if (len > 0)
*ppos += len;
+
+out_unlock:
+ kernfs_put_active(of->kn);
+ mutex_unlock(&of->mutex);
out_free:
- kfree(buf);
+ if (buf != of->prealloc_buf)
+ kfree(buf);
return len;
}
@@ -685,6 +690,14 @@ static int kernfs_fop_open(struct inode *inode, struct file *file)
*/
of->atomic_write_len = ops->atomic_write_len;
+ if (ops->prealloc) {
+ int len = of->atomic_write_len ?: PAGE_SIZE;
+ of->prealloc_buf = kmalloc(len + 1, GFP_KERNEL);
+ error = -ENOMEM;
+ if (!of->prealloc_buf)
+ goto err_free;
+ }
+
/*
* Always instantiate seq_file even if read access doesn't use
* seq_file or is not requested. This unifies private data access
@@ -715,6 +728,7 @@ static int kernfs_fop_open(struct inode *inode, struct file *file)
err_close:
seq_release(inode, file);
err_free:
+ kfree(of->prealloc_buf);
kfree(of);
err_out:
kernfs_put_active(kn);
@@ -728,6 +742,7 @@ static int kernfs_fop_release(struct inode *inode, struct file *filp)
kernfs_put_open_node(kn, of);
seq_release(inode, filp);
+ kfree(of->prealloc_buf);
kfree(of);
return 0;
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 589abee16a39..4ad3721a991c 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -184,6 +184,17 @@ static const struct kernfs_ops sysfs_file_kfops_rw = {
.write = sysfs_kf_write,
};
+static const struct kernfs_ops sysfs_prealloc_kfops_wo = {
+ .write = sysfs_kf_write,
+ .prealloc = true,
+};
+
+static const struct kernfs_ops sysfs_prealloc_kfops_rw = {
+ .seq_show = sysfs_kf_seq_show,
+ .write = sysfs_kf_write,
+ .prealloc = true,
+};
+
static const struct kernfs_ops sysfs_bin_kfops_ro = {
.read = sysfs_kf_bin_read,
};
@@ -222,13 +233,19 @@ int sysfs_add_file_mode_ns(struct kernfs_node *parent,
kobject_name(kobj)))
return -EINVAL;
- if (sysfs_ops->show && sysfs_ops->store)
- ops = &sysfs_file_kfops_rw;
- else if (sysfs_ops->show)
+ if (sysfs_ops->show && sysfs_ops->store) {
+ if (mode & SYSFS_PREALLOC)
+ ops = &sysfs_prealloc_kfops_rw;
+ else
+ ops = &sysfs_file_kfops_rw;
+ } else if (sysfs_ops->show)
ops = &sysfs_file_kfops_ro;
- else if (sysfs_ops->store)
- ops = &sysfs_file_kfops_wo;
- else
+ else if (sysfs_ops->store) {
+ if (mode & SYSFS_PREALLOC)
+ ops = &sysfs_prealloc_kfops_wo;
+ else
+ ops = &sysfs_file_kfops_wo;
+ } else
ops = &sysfs_file_kfops_empty;
size = PAGE_SIZE;
@@ -253,7 +270,7 @@ int sysfs_add_file_mode_ns(struct kernfs_node *parent,
if (!attr->ignore_lockdep)
key = attr->key ?: (struct lock_class_key *)&attr->skey;
#endif
- kn = __kernfs_create_file(parent, attr->name, mode, size, ops,
+ kn = __kernfs_create_file(parent, attr->name, mode & 0777, size, ops,
(void *)attr, ns, true, key);
if (IS_ERR(kn)) {
if (PTR_ERR(kn) == -EEXIST)
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 30faf797c2c3..d4e01b358341 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -179,6 +179,7 @@ struct kernfs_open_file {
struct mutex mutex;
int event;
struct list_head list;
+ char *prealloc_buf;
size_t atomic_write_len;
bool mmapped;
@@ -214,6 +215,13 @@ struct kernfs_ops {
* larger ones are rejected with -E2BIG.
*/
size_t atomic_write_len;
+ /*
+ * "prealloc" causes a buffer to be allocated at open for
+ * all read/write requests. As ->seq_show uses seq_read()
+ * which does its own allocation, it is incompatible with
+ * ->prealloc. Provide ->read and ->write with ->prealloc.
+ */
+ bool prealloc;
ssize_t (*write)(struct kernfs_open_file *of, char *buf, size_t bytes,
loff_t off);
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index f97d0dbb59fa..ddad16148bd6 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -70,6 +70,8 @@ struct attribute_group {
* for examples..
*/
+#define SYSFS_PREALLOC 010000
+
#define __ATTR(_name, _mode, _show, _store) { \
.attr = {.name = __stringify(_name), \
.mode = VERIFY_OCTAL_PERMISSIONS(_mode) }, \
@@ -77,6 +79,13 @@ struct attribute_group {
.store = _store, \
}
+#define __ATTR_PREALLOC(_name, _mode, _show, _store) { \
+ .attr = {.name = __stringify(_name), \
+ .mode = SYSFS_PREALLOC | VERIFY_OCTAL_PERMISSIONS(_mode) },\
+ .show = _show, \
+ .store = _store, \
+}
+
#define __ATTR_RO(_name) { \
.attr = { .name = __stringify(_name), .mode = S_IRUGO }, \
.show = _name##_show, \