[112/115] xfs: make sure sb_fdblocks is non-negative

Commit Message

Darrick J. Wong July 30, 2024, 12:52 a.m. UTC

From: Wengang Wang <[e-mail]>

Source kernel commit: 58f880711f2ba53fd5e959875aff5b3bf6d5c32e

A user with a completely full filesystem experienced an unexpected
shutdown when the filesystem tried to write the superblock during
runtime.
kernel shows the following dmesg:

[    8.176281] XFS (dm-4): Metadata corruption detected at xfs_sb_write_verify+0x60/0x120 [xfs], xfs_sb block 0x0
[    8.177417] XFS (dm-4): Unmount and run xfs_repair
[    8.178016] XFS (dm-4): First 128 bytes of corrupted metadata buffer:
[    8.178703] 00000000: 58 46 53 42 00 00 10 00 00 00 00 00 01 90 00 00  XFSB............
[    8.179487] 00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
[    8.180312] 00000020: cf 12 dc 89 ca 26 45 29 92 e6 e3 8d 3b b8 a2 c3  .....&E)....;...
[    8.181150] 00000030: 00 00 00 00 01 00 00 06 00 00 00 00 00 00 00 80  ................
[    8.182003] 00000040: 00 00 00 00 00 00 00 81 00 00 00 00 00 00 00 82  ................
[    8.182004] 00000050: 00 00 00 01 00 64 00 00 00 00 00 04 00 00 00 00  .....d..........
[    8.182004] 00000060: 00 00 64 00 b4 a5 02 00 02 00 00 08 00 00 00 00  ..d.............
[    8.182005] 00000070: 00 00 00 00 00 00 00 00 0c 09 09 03 17 00 00 19  ................
[    8.182008] XFS (dm-4): Corruption of in-memory data detected.  Shutting down filesystem
[    8.182010] XFS (dm-4): Please unmount the filesystem and rectify the problem(s)

When xfs_log_sb writes super block to disk, b_fdblocks is fetched from
m_fdblocks without any lock. As m_fdblocks can experience a positive ->
negative -> positive changing when the FS reaches fullness (see
xfs_mod_fdblocks). So there is a chance that sb_fdblocks is negative, and
because sb_fdblocks is type of unsigned long long, it reads super big.
And sb_fdblocks being bigger than sb_dblocks is a problem during log
recovery, xfs_validate_sb_write() complains.

Fix:
As sb_fdblocks will be re-calculated during mount when lazysbcount is
enabled, We just need to make xfs_validate_sb_write() happy -- make sure
sb_fdblocks is not nenative. This patch also takes care of other percpu
counters in xfs_log_sb.

Signed-off-by: Wengang Wang <[e-mail]>
Reviewed-by: Darrick J. Wong <[e-mail]>
Signed-off-by: Chandan Babu R <[e-mail]>
---
 libxfs/libxfs_priv.h |    2 +-
 libxfs/xfs_sb.c      |    7 ++++---
 2 files changed, 5 insertions(+), 4 deletions(-)

Patch

diff --git a/libxfs/libxfs_priv.h b/libxfs/libxfs_priv.h
index 64bc10e10..5d1aa23c7 100644
--- a/libxfs/libxfs_priv.h
+++ b/libxfs/libxfs_priv.h
@@ -210,7 +210,7 @@  static inline bool WARN_ON(bool expr) {
 #define WARN_ON_ONCE(e)			WARN_ON(e)
 #define percpu_counter_read(x)		(*x)
 #define percpu_counter_read_positive(x)	((*x) > 0 ? (*x) : 0)
-#define percpu_counter_sum(x)		(*x)
+#define percpu_counter_sum_positive(x)	((*x) > 0 ? (*x) : 0)
 
 /*
  * get_random_u32 is used for di_gen inode allocation, it must be zero for
diff --git a/libxfs/xfs_sb.c b/libxfs/xfs_sb.c
index f45ffd994..bedb36a06 100644
--- a/libxfs/xfs_sb.c
+++ b/libxfs/xfs_sb.c
@@ -1035,11 +1035,12 @@  xfs_log_sb(
 	 * and hence we don't need have to update it here.
 	 */
 	if (xfs_has_lazysbcount(mp)) {
-		mp->m_sb.sb_icount = percpu_counter_sum(&mp->m_icount);
+		mp->m_sb.sb_icount = percpu_counter_sum_positive(&mp->m_icount);
 		mp->m_sb.sb_ifree = min_t(uint64_t,
-				percpu_counter_sum(&mp->m_ifree),
+				percpu_counter_sum_positive(&mp->m_ifree),
 				mp->m_sb.sb_icount);
-		mp->m_sb.sb_fdblocks = percpu_counter_sum(&mp->m_fdblocks);
+		mp->m_sb.sb_fdblocks =
+				percpu_counter_sum_positive(&mp->m_fdblocks);
 	}
 
 	xfs_sb_to_disk(bp->b_addr, &mp->m_sb);