/*
* Buffer for holding data from partial reads which may happen since
* we’re rounding user read requests to a multiple of a max packet size.
+ *
+ * The pointer is initialised with NULL value and may be set by
+ * __ffs_epfile_read_data function to point to a temporary buffer.
+ *
+ * In normal operation, calls to __ffs_epfile_read_buffered will consume
+ * data from said buffer and eventually free it. Importantly, while the
+ * function is using the buffer, it sets the pointer to NULL. This is
+ * all right since __ffs_epfile_read_data and __ffs_epfile_read_buffered
+ * can never run concurrently (they are synchronised by epfile->mutex)
+ * so the latter will not assign a new value to the pointer.
+ *
+ * Meanwhile ffs_func_eps_disable frees the buffer (if the pointer is
+ * valid) and sets the pointer to READ_BUFFER_DROP value. This special
+ * value is crux of the synchronisation between ffs_func_eps_disable and
+ * __ffs_epfile_read_data.
+ *
+ * Once __ffs_epfile_read_data is about to finish it will try to set the
+ * pointer back to its old value (as described above), but seeing as the
+ * pointer is not-NULL (namely READ_BUFFER_DROP) it will instead free
+ * the buffer.
+ *
+ * == State transitions ==
+ *
+ * • ptr == NULL: (initial state)
+ * ◦ __ffs_epfile_read_buffer_free: go to ptr == DROP
+ * ◦ __ffs_epfile_read_buffered: nop
+ * ◦ __ffs_epfile_read_data allocates temp buffer: go to ptr == buf
+ * ◦ reading finishes: n/a, not in ‘and reading’ state
+ * • ptr == DROP:
+ * ◦ __ffs_epfile_read_buffer_free: nop
+ * ◦ __ffs_epfile_read_buffered: go to ptr == NULL
+ * ◦ __ffs_epfile_read_data allocates temp buffer: free buf, nop
+ * ◦ reading finishes: n/a, not in ‘and reading’ state
+ * • ptr == buf:
+ * ◦ __ffs_epfile_read_buffer_free: free buf, go to ptr == DROP
+ * ◦ __ffs_epfile_read_buffered: go to ptr == NULL and reading
+ * ◦ __ffs_epfile_read_data: n/a, __ffs_epfile_read_buffered
+ * is always called first
+ * ◦ reading finishes: n/a, not in ‘and reading’ state
+ * • ptr == NULL and reading:
+ * ◦ __ffs_epfile_read_buffer_free: go to ptr == DROP and reading
+ * ◦ __ffs_epfile_read_buffered: n/a, mutex is held
+ * ◦ __ffs_epfile_read_data: n/a, mutex is held
+ * ◦ reading finishes and …
+ * … all data read: free buf, go to ptr == NULL
+ * … otherwise: go to ptr == buf and reading
+ * • ptr == DROP and reading:
+ * ◦ __ffs_epfile_read_buffer_free: nop
+ * ◦ __ffs_epfile_read_buffered: n/a, mutex is held
+ * ◦ __ffs_epfile_read_data: n/a, mutex is held
+ * ◦ reading finishes: free buf, go to ptr == DROP
*/
- struct ffs_buffer *read_buffer; /* P: epfile->mutex */
+ struct ffs_buffer *read_buffer;
+#define READ_BUFFER_DROP ((struct ffs_buffer *)ERR_PTR(-ESHUTDOWN))
char name[5];
schedule_work(&io_data->work);
}
+static void __ffs_epfile_read_buffer_free(struct ffs_epfile *epfile)
+{
+ /*
+ * See comment in struct ffs_epfile for full read_buffer pointer
+ * synchronisation story.
+ */
+ struct ffs_buffer *buf = xchg(&epfile->read_buffer, READ_BUFFER_DROP);
+ if (buf && buf != READ_BUFFER_DROP)
+ kfree(buf);
+}
+
/* Assumes epfile->mutex is held. */
static ssize_t __ffs_epfile_read_buffered(struct ffs_epfile *epfile,
struct iov_iter *iter)
{
- struct ffs_buffer *buf = epfile->read_buffer;
+ /*
+ * Null out epfile->read_buffer so ffs_func_eps_disable does not free
+ * the buffer while we are using it. See comment in struct ffs_epfile
+ * for full read_buffer pointer synchronisation story.
+ */
+ struct ffs_buffer *buf = xchg(&epfile->read_buffer, NULL);
ssize_t ret;
- if (!buf)
+ if (!buf || buf == READ_BUFFER_DROP)
return 0;
ret = copy_to_iter(buf->data, buf->length, iter);
if (buf->length == ret) {
kfree(buf);
- epfile->read_buffer = NULL;
- } else if (unlikely(iov_iter_count(iter))) {
+ return ret;
+ }
+
+ if (unlikely(iov_iter_count(iter))) {
ret = -EFAULT;
} else {
buf->length -= ret;
buf->data += ret;
}
+
+ if (cmpxchg(&epfile->read_buffer, NULL, buf))
+ kfree(buf);
+
return ret;
}
buf->length = data_len;
buf->data = buf->storage;
memcpy(buf->storage, data + ret, data_len);
- epfile->read_buffer = buf;
+
+ /*
+ * At this point read_buffer is NULL or READ_BUFFER_DROP (if
+ * ffs_func_eps_disable has been called in the meanwhile). See comment
+ * in struct ffs_epfile for full read_buffer pointer synchronisation
+ * story.
+ */
+ if (unlikely(cmpxchg(&epfile->read_buffer, NULL, buf)))
+ kfree(buf);
return ret;
}
ENTER();
- kfree(epfile->read_buffer);
- epfile->read_buffer = NULL;
+ __ffs_epfile_read_buffer_free(epfile);
ffs_data_closed(epfile->ffs);
return 0;
unsigned count = func->ffs->eps_count;
unsigned long flags;
+ spin_lock_irqsave(&func->ffs->eps_lock, flags);
do {
- if (epfile)
- mutex_lock(&epfile->mutex);
- spin_lock_irqsave(&func->ffs->eps_lock, flags);
/* pending requests get nuked */
if (likely(ep->ep))
usb_ep_disable(ep->ep);
++ep;
- spin_unlock_irqrestore(&func->ffs->eps_lock, flags);
if (epfile) {
epfile->ep = NULL;
- kfree(epfile->read_buffer);
- epfile->read_buffer = NULL;
- mutex_unlock(&epfile->mutex);
+ __ffs_epfile_read_buffer_free(epfile);
++epfile;
}
} while (--count);
+ spin_unlock_irqrestore(&func->ffs->eps_lock, flags);
}
static int ffs_func_eps_enable(struct ffs_function *func)
projects / cascardo / linux.git / blobdiff