f2fs: don't drop the top folio order in the f2fs_iostat tracepoint

The f2fs_iostat tracepoint stores the per-order read folio counts in a
fixed-size array and prints a fixed number of buckets, both hardcoded to
11. The sysfs iostat accounting array is instead sized by NR_PAGE_ORDERS
(= MAX_PAGE_ORDER + 1), which is not always 11:

	arm64 16K pages -> MAX_PAGE_ORDER 11 -> NR_PAGE_ORDERS 12
	arm64 64K pages -> MAX_PAGE_ORDER 13 -> NR_PAGE_ORDERS 14

f2fs enables large folios for immutable, non-compressed files, and the
read folio order is bounded by MAX_PAGECACHE_ORDER, i.e.
min(MAX_XAS_ORDER, PREFERRED_MAX_PAGECACHE_ORDER). With THP enabled this
reaches order 11 on 16K/64K base-page kernels (MAX_XAS_ORDER caps it at
11). So an order-11 read folio is possible there and is accounted into
index 11 of the array.

On those configurations the sysfs file reports the order-11 count
correctly, but the tracepoint silently drops it: the memcpy is capped at
min(NR_PAGE_ORDERS, 11), so index 11 is never copied and the trace
disagrees with sysfs. There is no memory-safety issue, only the order-11
bucket missing from the trace; 4K-page kernels (NR_PAGE_ORDERS == 11,
max order <= 9) are unaffected.

Size the array and the printed buckets by a ceiling that covers the
largest possible NR_PAGE_ORDERS (14) with headroom, and add a
BUILD_BUG_ON() so any future growth of NR_PAGE_ORDERS fails the build
loudly instead of silently truncating again. The human-readable
"order=count" output is preserved.

Fixes: cb8ff3ead9a3 ("f2fs: add page-order information for large folio reads in iostat")
Cc: stable@vger.kernel.org
Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 16 insertions, 4 deletions

diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
index 270c1a2c24c4..1dd9fc5afc46 100644
--- a/include/trace/events/f2fs.h
+++ b/include/trace/events/f2fs.h
@@ -2114,6 +2114,14 @@ DEFINE_EVENT(f2fs_zip_end, f2fs_decompress_pages_end,
 );
 
 #ifdef CONFIG_F2FS_IOSTAT
+/*
+ * Number of read folio order buckets emitted by the f2fs_iostat tracepoint.
+ * TP_printk() cannot loop, so the field count is fixed here and must be >=
+ * the largest possible NR_PAGE_ORDERS (14 on arm64 with 64K pages). The
+ * BUILD_BUG_ON() in f2fs_update_read_folio_count() enforces this.
+ */
+#define F2FS_IOSTAT_RD_FOLIO_ORDERS	16
+
 TRACE_EVENT(f2fs_iostat,
 
 	TP_PROTO(struct f2fs_sb_info *sbi, unsigned long long *iostat,
@@ -2151,7 +2159,7 @@ TRACE_EVENT(f2fs_iostat,
 		__field(unsigned long long,	fs_mrio)
 		__field(unsigned long long,	fs_discard)
 		__field(unsigned long long,	fs_reset_zone)
-		__array(unsigned long long,	read_folio_count, 11)
+		__array(unsigned long long,	read_folio_count, F2FS_IOSTAT_RD_FOLIO_ORDERS)
 	),
 
 	TP_fast_assign(
@@ -2186,7 +2194,8 @@ TRACE_EVENT(f2fs_iostat,
 		__entry->fs_reset_zone	= iostat[FS_ZONE_RESET_IO];
 		memset(__entry->read_folio_count, 0, sizeof(__entry->read_folio_count));
 		memcpy(__entry->read_folio_count, read_folio_count,
-				sizeof(unsigned long long) * min_t(int, NR_PAGE_ORDERS, 11));
+				sizeof(unsigned long long) *
+				min_t(int, NR_PAGE_ORDERS, F2FS_IOSTAT_RD_FOLIO_ORDERS));
 	),
 
 	TP_printk("dev = (%d,%d), "
@@ -2201,7 +2210,8 @@ TRACE_EVENT(f2fs_iostat,
 		"fs [data=%llu, (gc_data=%llu, cdata=%llu), "
 		"node=%llu, meta=%llu], "
 		"read_folio_count [0=%llu, 1=%llu, 2=%llu, 3=%llu, 4=%llu, "
-		"5=%llu, 6=%llu, 7=%llu, 8=%llu, 9=%llu, 10=%llu]",
+		"5=%llu, 6=%llu, 7=%llu, 8=%llu, 9=%llu, 10=%llu, 11=%llu, "
+		"12=%llu, 13=%llu, 14=%llu, 15=%llu]",
 		show_dev(__entry->dev), __entry->app_wio, __entry->app_dio,
 		__entry->app_bio, __entry->app_mio, __entry->app_bcdio,
 		__entry->app_mcdio, __entry->fs_dio, __entry->fs_cdio,
@@ -2218,7 +2228,9 @@ TRACE_EVENT(f2fs_iostat,
 		__entry->read_folio_count[4], __entry->read_folio_count[5],
 		__entry->read_folio_count[6], __entry->read_folio_count[7],
 		__entry->read_folio_count[8], __entry->read_folio_count[9],
-		__entry->read_folio_count[10])
+		__entry->read_folio_count[10], __entry->read_folio_count[11],
+		__entry->read_folio_count[12], __entry->read_folio_count[13],
+		__entry->read_folio_count[14], __entry->read_folio_count[15])
 );
 
 #ifndef __F2FS_IOSTAT_LATENCY_TYPE