UBI: fix races in I/O debugging checks
When paranoid checs are enabled, the 'io_paral' test from the
'mtd-utils' package fails. The symptoms are:
UBI error: paranoid_check_all_ff: flash region at PEB 3973:512, length 15872 does not contain all 0xFF bytes
UBI error: paranoid_check_all_ff: paranoid check failed for PEB 3973
UBI: hex dump of the 512-16384 region
It turned out to be a bug in the checking function. Suppose there
are 2 tasks - A and B. Task A is the wear-levelling working
('wear_leveling_worker()'). It is reading the VID header to find
which LEB this PEB belongs to. Say, task A is reading header
of PEB X. Suppose PEB X is unmapped, and has no VID header.
Task B is trying to write to PEB X.
Task A: in 'ubi_io_read_vid_hdr()': reads the VID header from PEB X.
The read data contain all 0xFF bytes.
Task B: writes VID header and some data to PEB X
Task A: assumes PEB X is empty, calls 'paranoid_check_all_ff()', which
fails.
The solution for this problem is to make 'paranoid_check_all_ff()'
re-read the VID header, re-check it, and only if it is not there,
check the rest. This now implemented by the 'paranoid_check_empty()'
function.
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/drivers/mtd/ubi/io.c b/drivers/mtd/ubi/io.c
index fe81039..ac6604a 100644
--- a/drivers/mtd/ubi/io.c
+++ b/drivers/mtd/ubi/io.c
@@ -100,6 +100,7 @@
const struct ubi_vid_hdr *vid_hdr);
static int paranoid_check_all_ff(struct ubi_device *ubi, int pnum, int offset,
int len);
+static int paranoid_check_empty(struct ubi_device *ubi, int pnum);
#else
#define paranoid_check_not_bad(ubi, pnum) 0
#define paranoid_check_peb_ec_hdr(ubi, pnum) 0
@@ -107,6 +108,7 @@
#define paranoid_check_peb_vid_hdr(ubi, pnum) 0
#define paranoid_check_vid_hdr(ubi, pnum, vid_hdr) 0
#define paranoid_check_all_ff(ubi, pnum, offset, len) 0
+#define paranoid_check_empty(ubi, pnum) 0
#endif
/**
@@ -670,11 +672,6 @@
if (read_err != -EBADMSG &&
check_pattern(ec_hdr, 0xFF, UBI_EC_HDR_SIZE)) {
/* The physical eraseblock is supposedly empty */
-
- /*
- * The below is just a paranoid check, it has to be
- * compiled out if paranoid checks are disabled.
- */
err = paranoid_check_all_ff(ubi, pnum, 0,
ubi->peb_size);
if (err)
@@ -955,8 +952,7 @@
* The below is just a paranoid check, it has to be
* compiled out if paranoid checks are disabled.
*/
- err = paranoid_check_all_ff(ubi, pnum, ubi->leb_start,
- ubi->leb_size);
+ err = paranoid_check_empty(ubi, pnum);
if (err)
return err > 0 ? UBI_IO_BAD_VID_HDR : err;
@@ -1280,4 +1276,74 @@
return err;
}
+/**
+ * paranoid_check_empty - whether a PEB is empty.
+ * @ubi: UBI device description object
+ * @pnum: the physical eraseblock number to check
+ *
+ * This function makes sure PEB @pnum is empty, which means it contains only
+ * %0xFF data bytes. Returns zero if the PEB is empty, %1 if not, and a
+ * negative error code in case of failure.
+ *
+ * Empty PEBs have the EC header, and do not have the VID header. The caller of
+ * this function should have already made sure the PEB does not have the VID
+ * header. However, this function re-checks that, because it is possible that
+ * the header and data has already been written to the PEB.
+ *
+ * Let's consider a possible scenario. Suppose there are 2 tasks - A and B.
+ * Task A is in 'wear_leveling_worker()'. It is reading VID header of PEB X to
+ * find which LEB it corresponds to. PEB X is currently unmapped, and has no
+ * VID header. Task B is trying to write to PEB X.
+ *
+ * Task A: in 'ubi_io_read_vid_hdr()': reads the VID header from PEB X. The
+ * read data contain all 0xFF bytes;
+ * Task B: writes VID header and some data to PEB X;
+ * Task A: assumes PEB X is empty, calls 'paranoid_check_empty()'. And if we
+ * do not re-read the VID header, and do not cancel the checking if it
+ * is there, we fail.
+ */
+static int paranoid_check_empty(struct ubi_device *ubi, int pnum)
+{
+ int err, offs = ubi->vid_hdr_aloffset, len = ubi->vid_hdr_alsize;
+ size_t read;
+ uint32_t magic;
+ const struct ubi_vid_hdr *vid_hdr;
+
+ mutex_lock(&ubi->dbg_buf_mutex);
+ err = ubi->mtd->read(ubi->mtd, offs, len, &read, ubi->dbg_peb_buf);
+ if (err && err != -EUCLEAN) {
+ ubi_err("error %d while reading %d bytes from PEB %d:%d, "
+ "read %zd bytes", err, len, pnum, offs, read);
+ goto error;
+ }
+
+ vid_hdr = ubi->dbg_peb_buf;
+ magic = be32_to_cpu(vid_hdr->magic);
+ if (magic == UBI_VID_HDR_MAGIC)
+ /* The PEB contains VID header, so it is not empty */
+ goto out;
+
+ err = check_pattern(ubi->dbg_peb_buf, 0xFF, len);
+ if (err == 0) {
+ ubi_err("flash region at PEB %d:%d, length %d does not "
+ "contain all 0xFF bytes", pnum, offs, len);
+ goto fail;
+ }
+
+out:
+ mutex_unlock(&ubi->dbg_buf_mutex);
+ return 0;
+
+fail:
+ ubi_err("paranoid check failed for PEB %d", pnum);
+ ubi_msg("hex dump of the %d-%d region", offs, offs + len);
+ print_hex_dump(KERN_DEBUG, "", DUMP_PREFIX_OFFSET, 32, 1,
+ ubi->dbg_peb_buf, len, 1);
+ err = 1;
+error:
+ ubi_dbg_dump_stack();
+ mutex_unlock(&ubi->dbg_buf_mutex);
+ return err;
+}
+
#endif /* CONFIG_MTD_UBI_DEBUG_PARANOID */