diff options
| -rw-r--r-- | fs/ubifs/recovery.c | 152 |
1 files changed, 87 insertions, 65 deletions
diff --git a/fs/ubifs/recovery.c b/fs/ubifs/recovery.c index 6adb5328a016..783d8e0beb76 100644 --- a/fs/ubifs/recovery.c +++ b/fs/ubifs/recovery.c @@ -564,19 +564,15 @@ static int fix_unclean_leb(struct ubifs_info *c, struct ubifs_scan_leb *sleb, } /** - * drop_last_node - drop the last node or group of nodes. + * drop_last_group - drop the last 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 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. + * group of nodes of the scanned LEB. */ -static int drop_last_node(struct ubifs_scan_leb *sleb, int *offs, int grouped) +static void drop_last_group(struct ubifs_scan_leb *sleb, int *offs) { - int dropped = 0; - while (!list_empty(&sleb->nodes)) { struct ubifs_scan_node *snod; struct ubifs_ch *ch; @@ -585,17 +581,40 @@ static int drop_last_node(struct ubifs_scan_leb *sleb, int *offs, int grouped) list); ch = snod->node; if (ch->group_type != UBIFS_IN_NODE_GROUP) - return dropped; - dbg_rcvry("dropping node at %d:%d", sleb->lnum, snod->offs); + break; + + dbg_rcvry("dropping grouped node at %d:%d", + sleb->lnum, snod->offs); + *offs = snod->offs; + list_del(&snod->list); + kfree(snod); + sleb->nodes_cnt -= 1; + } +} + +/** + * drop_last_node - drop the last node. + * @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 is a helper function for 'ubifs_recover_leb()' which drops the last + * node of the scanned LEB. + */ +static void drop_last_node(struct ubifs_scan_leb *sleb, int *offs) +{ + struct ubifs_scan_node *snod; + + if (!list_empty(&sleb->nodes)) { + snod = list_entry(sleb->nodes.prev, struct ubifs_scan_node, + list); + + dbg_rcvry("dropping last node at %d:%d", sleb->lnum, snod->offs); *offs = snod->offs; list_del(&snod->list); kfree(snod); sleb->nodes_cnt -= 1; - dropped = 1; - if (!grouped) - break; } - return dropped; } /** @@ -697,59 +716,62 @@ struct ubifs_scan_leb *ubifs_recover_leb(struct ubifs_info *c, int lnum, * If nodes are grouped, always drop the incomplete group at * the end. */ - drop_last_node(sleb, &offs, 1); + drop_last_group(sleb, &offs); - /* - * 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 nodes 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)); + if (jhead == GCHD) { + /* + * If this LEB belongs to the GC head then 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 nodes 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? Why + * 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. + * + * Imagine the file-system is full, we run GC which starts + * 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 (offs > min_io_unit) + drop_last_node(sleb, &offs); + } buf = sbuf + offs; len = c->leb_size - offs; |