gspca: Fix locking issues related to suspend/resume

Hello Hans Verkuil,

This is a semi-automatic email about new static checker warnings.

The patch 254902b01d2a: "[media] gspca: Fix locking issues related to suspend/resume" from May 6, 2012, leads to the following Smatch complaint:

drivers/media/video/gspca/sq905c.c:176 sq905c_dostream()

	 warn: variable dereferenced before check 'gspca_dev->dev' (see line 180)

drivers/media/video/gspca/sq905c.c
158 /* Request the header, which tells the size to download */
159 ret = usb_bulk_msg(gspca_dev->dev,
160 usb_rcvbulkpipe(gspca_dev->dev, 0x81),

                                                        ^^^^^^^^^^^^^^

Derereference inside the calls to usb_bulk_msg() and usb_rcvbulkpipe().

161 buffer, FRAME_HEADER_LEN, &act_len,
162 SQ905C_DATA_TIMEOUT);
163 PDEBUG(D_STREAM,
164 "Got %d bytes out of %d for header",
165 act_len, FRAME_HEADER_LEN);
166 if (ret < 0 || act_len < FRAME_HEADER_LEN)
167 goto quit_stream;
168 /* size is read from 4 bytes starting 0x40, little endian */
169 bytes_left = buffer[0x40]|(buffer[0x41]<<8)|(buffer[0x42]<<16)
170 |(buffer[0x43]<<24);

   171                  PDEBUG(D_STREAM, "bytes_left = 0x%x", bytes_left);
   172                  /* We keep the header. It has other information, too. */
   173                  packet_type = FIRST_PACKET;
   174                  gspca_frame_add(gspca_dev, packet_type,
   175                                  buffer, FRAME_HEADER_LEN);
   176			while (bytes_left > 0 && gspca_dev->dev) {
                                                 ^^^^^^^^^^^^^^

New check.

177 data_len = bytes_left > SQ905C_MAX_TRANSFER ?
178 SQ905C_MAX_TRANSFER : bytes_left;
179 ret = usb_bulk_msg(gspca_dev->dev,
180 usb_rcvbulkpipe(gspca_dev->dev, 0x81),

                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Some more dereferences here.

   181					buffer, data_len, &act_len,
   182					SQ905C_DATA_TIMEOUT);
   183                          if (ret < 0 || act_len < data_len)
   184                                  goto quit_stream;
   185                          PDEBUG(D_STREAM,
   186                                  "Got %d bytes out of %d for frame",
   187                                  data_len, bytes_left);
   188                          bytes_left -= data_len;
   189                          if (bytes_left == 0)
   190                                  packet_type = LAST_PACKET;
   191                          else
   192                                  packet_type = INTER_PACKET;
   193                          gspca_frame_add(gspca_dev, packet_type,
   194                                          buffer, data_len);
   195                  }

regards,
dan carpenter

Hi,

Thanks for the report, it turns out that the checking for gspca_dev->dev, rather then gspca_dev->present (which is a mod I made on top of Hans Verkuil's orginal patch), turns out to be a bad idea in general as its racy, this race has been fixed by this commit:
http://git.linuxtv.org/hgoede/gspca.git/commitdiff/a454f0811950742475b76dbf5ac10876e48ffaaa

Which should also appease the static checker warnings.

Thanks & Regards,

Hans