diff options
| -rw-r--r-- | fs/ubifs/recovery.c | 82 |
1 files changed, 72 insertions, 10 deletions
diff --git a/fs/ubifs/recovery.c b/fs/ubifs/recovery.c index 74281f1..731d9e2 100644 --- a/fs/ubifs/recovery.c +++ b/fs/ubifs/recovery.c @@ -564,13 +564,16 @@ static int fix_unclean_leb(struct ubifs_info *c, struct ubifs_scan_leb *sleb, } /** - * drop_incomplete_group - drop nodes from an incomplete group. + * drop_last_node - drop the last node or group of nodes. * @sleb: scanned LEB information * @offs: offset of dropped nodes is returned here + * @grouped: non-zero if whole group of nodes have to be dropped * - * This function returns %1 if nodes are dropped and %0 otherwise. + * This is a helper function for 'ubifs_recover_leb()' which drops the last + * node of the scanned LEB or the last group of nodes if @grouped is not zero. + * This function returns %1 if a node was dropped and %0 otherwise. */ -static int drop_incomplete_group(struct ubifs_scan_leb *sleb, int *offs) +static int drop_last_node(struct ubifs_scan_leb *sleb, int *offs, int grouped) { int dropped = 0; @@ -589,6 +592,8 @@ static int drop_incomplete_group(struct ubifs_scan_leb *sleb, int *offs) kfree(snod); sleb->nodes_cnt -= 1; dropped = 1; + if (!grouped) + break; } return dropped; } @@ -609,8 +614,7 @@ static int drop_incomplete_group(struct ubifs_scan_leb *sleb, int *offs) struct ubifs_scan_leb *ubifs_recover_leb(struct ubifs_info *c, int lnum, int offs, void *sbuf, int grouped) { - int ret = 0, err, len = c->leb_size - offs; - int start = offs; + int ret = 0, err, len = c->leb_size - offs, start = offs, min_io_unit; struct ubifs_scan_leb *sleb; void *buf = sbuf + offs; @@ -620,6 +624,7 @@ struct ubifs_scan_leb *ubifs_recover_leb(struct ubifs_info *c, int lnum, if (IS_ERR(sleb)) return sleb; + ubifs_assert(len >= 8); while (len >= 8) { dbg_scan("look at LEB %d:%d (%d bytes left)", lnum, offs, len); @@ -684,11 +689,68 @@ struct ubifs_scan_leb *ubifs_recover_leb(struct ubifs_info *c, int lnum, } } - /* Drop nodes from incomplete group */ - if (grouped && drop_incomplete_group(sleb, &offs)) { - buf = sbuf + offs; - len = c->leb_size - offs; - } + min_io_unit = round_down(offs, c->min_io_size); + if (grouped) + /* + * If nodes are grouped, always drop the incomplete group at + * the end. + */ + drop_last_node(sleb, &offs, 1); + + /* + * While we are in the middle of the same min. I/O unit keep dropping + * nodes. So basically, what we want is to make sure that the last min. + * I/O unit where we saw the corruption is dropped completely with all + * the uncorrupted node which may possibly sit there. + * + * In other words, let's name the min. I/O unit where the corruption + * starts B, and the previous min. I/O unit A. The below code tries to + * deal with a situation when half of B contains valid nodes or the end + * of a valid node, and the second half of B contains corrupted data or + * garbage. This means that UBIFS had been writing to B just before the + * power cut happened. I do not know how realistic is this scenario + * that half of the min. I/O unit had been written successfully and the + * other half not, but this is possible in our 'failure mode emulation' + * infrastructure at least. + * + * So what is the problem, why we need to drop those nodes? Whey can't + * we just clean-up the second half of B by putting a padding node + * there? We can, and this works fine with one exception which was + * reproduced with power cut emulation testing and happens extremely + * rarely. The description follows, but it is worth noting that that is + * only about the GC head, so we could do this trick only if the bud + * belongs to the GC head, but it does not seem to be worth an + * additional "if" statement. + * + * So, imagine the file-system is full, we run GC which is moving valid + * nodes from LEB X to LEB Y (obviously, LEB Y is the current GC head + * LEB). The @c->gc_lnum is -1, which means that GC will retain LEB X + * and will try to continue. Imagine that LEB X is currently the + * dirtiest LEB, and the amount of used space in LEB Y is exactly the + * same as amount of free space in LEB X. + * + * And a power cut happens when nodes are moved from LEB X to LEB Y. We + * are here trying to recover LEB Y which is the GC head LEB. We find + * the min. I/O unit B as described above. Then we clean-up LEB Y by + * padding min. I/O unit. And later 'ubifs_rcvry_gc_commit()' function + * fails, because it cannot find a dirty LEB which could be GC'd into + * LEB Y! Even LEB X does not match because the amount of valid nodes + * there does not fit the free space in LEB Y any more! And this is + * because of the padding node which we added to LEB Y. The + * user-visible effect of this which I once observed and analysed is + * that we cannot mount the file-system with -ENOSPC error. + * + * So obviously, to make sure that situation does not happen we should + * free min. I/O unit B in LEB Y completely and the last used min. I/O + * unit in LEB Y should be A. This is basically what the below code + * tries to do. + */ + while (min_io_unit == round_down(offs, c->min_io_size) && + min_io_unit != offs && + drop_last_node(sleb, &offs, grouped)); + + buf = sbuf + offs; + len = c->leb_size - offs; clean_buf(c, &buf, lnum, &offs, &len); ubifs_end_scan(c, sleb, lnum, offs); |
