[Ocfs2-devel] [PATCH] ocfs2: Fix wrong search logic in __ocfs2_resv_find_window - Heming Zhao via Ocfs2-devel

From: Heming Zhao via Ocfs2-devel <ocfs2-devel@oss.oracle.com>
To: joseph.qi@linux.alibaba.com
Cc: ocfs2-devel@oss.oracle.com
Subject: [Ocfs2-devel] [PATCH] ocfs2: Fix wrong search logic in __ocfs2_resv_find_window
Date: Thu,  6 Apr 2023 23:40:52 +0800	[thread overview]
Message-ID: <20230406154052.9863-1-heming.zhao@suse.com> (raw)

** problem **

Current code triggers a defragfs bug [1]:

```
tw-tst:~ # defragfs.ocfs2 /mnt/test_from_dd1
defragfs.ocfs2 1.8.7
[ERROR]Move extent failed:"/mnt/test_from_dd1" - No space left on device
[ERROR]"/mnt/test_from_dd1":No space left on device
```

I added some debug messages in relevant functions. When above error
messages appeared, the la-window still had enough continuous bitmap
to use, the -ENOSPC is wrong.

** analysis **

__ocfs2_resv_find_window should use resv node from rb-tree to do linear
search. But current code logic uses un-managered area between two resvs.
The searching logic deviates from this func job, which should only focus
on reservation areas (when rb_root is non NULL). Another issue of
__ocfs2_resv_find_window is more inclined to generate inner fragment.
It doesn't search & consume existing reservations but be apt to create
new reservation item.

This patch pulls this func (__ocfs2_resv_find_window) to do what it
should do: search & consume resev. if this func fails to get suitable
bitmap area, caller ocfs2_resv_find_window fallbacks to use oldest
resv from LRU to do the final search.

[1]: https://bugzilla.suse.com/show_bug.cgi?id=1131931

Signed-off-by: Heming Zhao <heming.zhao@suse.com>
---
 fs/ocfs2/reservations.c | 48 +++++++++++++++++++++++++++++------------
 1 file changed, 34 insertions(+), 14 deletions(-)

diff --git a/fs/ocfs2/reservations.c b/fs/ocfs2/reservations.c
index a9d1296d736d..eda672622d1d 100644
--- a/fs/ocfs2/reservations.c
+++ b/fs/ocfs2/reservations.c
@@ -458,10 +458,11 @@ static void __ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
 {
 	struct rb_root *root = &resmap->m_reservations;
 	unsigned int gap_start, gap_end, gap_len;
-	struct ocfs2_alloc_reservation *prev_resv, *next_resv;
+	struct ocfs2_alloc_reservation *prev_resv, *next_resv, *best_resv;
 	struct rb_node *prev, *next;
 	unsigned int cstart, clen;
 	unsigned int best_start = 0, best_len = 0;
+	int create_new = 0;
 
 	/*
 	 * Nasty cases to consider:
@@ -540,8 +541,9 @@ static void __ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
 		if (clen) {
 			best_len = clen;
 			best_start = cstart;
+			create_new = 1;
 			if (best_len == wanted)
-				goto out_insert;
+				goto out_create;
 		}
 
 		prev_resv = next_resv;
@@ -557,13 +559,9 @@ static void __ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
 	while (1) {
 		next = rb_next(prev);
 		if (next) {
-			next_resv = rb_entry(next,
-					     struct ocfs2_alloc_reservation,
-					     r_node);
-
-			gap_start = ocfs2_resv_end(prev_resv) + 1;
-			gap_end = next_resv->r_start - 1;
-			gap_len = gap_end - gap_start + 1;
+			gap_start = prev_resv->r_start;
+			gap_end = prev_resv->r_start + prev_resv->r_len - 1;
+			gap_len = prev_resv->r_len;
 		} else {
 			/*
 			 * We're at the rightmost edge of the
@@ -575,8 +573,8 @@ static void __ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
 			gap_end = resmap->m_bitmap_len - 1;
 		}
 
-		trace_ocfs2_resv_find_window_next(next ? next_resv->r_start: -1,
-					next ? ocfs2_resv_end(next_resv) : -1);
+		trace_ocfs2_resv_find_window_next(next ? prev_resv->r_start : -1,
+					next ? ocfs2_resv_end(prev_resv) : -1);
 		/*
 		 * No need to check this gap if we have already found
 		 * a larger region of free bits.
@@ -589,10 +587,16 @@ static void __ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
 		if (clen == wanted) {
 			best_len = clen;
 			best_start = cstart;
-			goto out_insert;
+			best_resv = prev_resv;
+			if (!next)
+				goto out_create;
+			else
+				goto out_insert;
 		} else if (clen > best_len) {
 			best_len = clen;
 			best_start = cstart;
+			best_resv = prev_resv;
+			create_new = 0;
 		}
 
 next_resv:
@@ -604,12 +608,28 @@ static void __ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
 				     r_node);
 	}
 
-out_insert:
-	if (best_len) {
+	if (!best_len)
+		return;
+
+	if (create_new) {
+out_create:
 		resv->r_start = best_start;
 		resv->r_len = best_len;
 		ocfs2_resv_insert(resmap, resv);
+		return;
 	}
+
+out_insert:
+	if (best_resv->r_len <= wanted) {
+		resv->r_start = best_start;
+		resv->r_len = best_len;
+		__ocfs2_resv_discard(resmap, best_resv);
+	} else {
+		best_resv->r_len -= best_len;
+		resv->r_start = ocfs2_resv_end(best_resv) + 1;
+		resv->r_len = best_len;
+	}
+	ocfs2_resv_insert(resmap, resv);
 }
 
 static void ocfs2_cannibalize_resv(struct ocfs2_reservation_map *resmap,
-- 
2.26.2


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