Hi,
在 2025/08/26 0:08, Meir Elisha 写道:
Hi Kuai
Appreciate your thoughts on V3. Thanks in advance.
On 8/19/25 10:38, Meir Elisha wrote:
When operating in write-through journal mode, a journal device failure
can lead to parity corruption and silent data loss.
This occurs because the current implementation continues to update
parity even when journal writes fail, violating the write-through
consistency guarantee.
Signed-off-by: Meir Elisha <meir.elisha@xxxxxxxxxxx>
---
Changes in v3:
- Remove unnecessary braces in ops_run_io()
- Adding comment on clearing the R5_Want* flags
Changes in v2:
- Drop writes only when s->failed > conf->max_degraded
- Remove changes in handle_stripe()
Wrote a script for showcasing the issue.
#!/bin/bash
set -e
RAID_DEV="/dev/md127"
DATA_OFFSET=32
# Arrays to store disk states
declare -a BEFORE_BYTES
declare -a DISK_NAMES
cleanup() {
mdadm --stop $RAID_DEV 2>/dev/null || true
dmsetup remove disk0-flakey disk1-flakey journal-flakey 2>/dev/null || true
for i in {10..15}; do
losetup -d /dev/loop$i 2>/dev/null || true
done
rm -f /tmp/disk*.img 2>/dev/null || true
}
# Function to read first byte from device at offset
read_first_byte() {
local device=$1
local offset=$2
dd if=$device bs=32k skip=$offset count=4 iflag=direct status=none | head -c 1 | xxd -p
}
# Function to calculate which disk holds parity for a given stripe
# RAID5 left-symmetric algorithm (default)
get_parity_disk() {
local stripe_num=$1
local n_disks=$2
local pd_idx=$((($n_disks - 1) - ($stripe_num % $n_disks)))
echo $pd_idx
}
cleanup
echo "=== RAID5 Parity Bug Test ==="
echo
# Create backing files
for i in {0..5}; do
dd if=/dev/zero of=/tmp/disk$i.img bs=1M count=100 status=none
losetup /dev/loop$((10+i)) /tmp/disk$i.img
done
SIZE=$(blockdev --getsz /dev/loop10)
# Create normal linear targets first
dmsetup create disk0-flakey --table "0 $SIZE linear /dev/loop10 0"
dmsetup create disk1-flakey --table "0 $SIZE linear /dev/loop11 0"
dmsetup create journal-flakey --table "0 $SIZE linear /dev/loop15 0"
# Create RAID5 using the dm devices
echo "1. Creating RAID5 array..."
mdadm --create $RAID_DEV --chunk=32K --level=5 --raid-devices=5 \
/dev/mapper/disk0-flakey \
/dev/mapper/disk1-flakey \
/dev/loop12 /dev/loop13 /dev/loop14 \
--write-journal /dev/mapper/journal-flakey \
--assume-clean --force
echo "write-through" > /sys/block/md127/md/journal_mode
echo 0 > /sys/block/md127/md/safe_mode_delay
# Write test pattern
echo "2. Writing test pattern..."
for i in 0 1 2 3; do
VAL=$((1 << i))
echo "VAL:$VAL"
perl -e "print chr($VAL) x 32768" | dd of=$RAID_DEV bs=32k count=1 seek=$i oflag=direct status=none
done
sync
sleep 1 # Give time for writes to settle
echo "3. Reading disk states before failure..."
# Calculate parity disk for stripe 0 (first 32k chunk)
STRIPE_NUM=0
N_DISKS=5
PARITY_INDEX=$(get_parity_disk $STRIPE_NUM $N_DISKS)
echo "Calculated parity disk index for stripe $STRIPE_NUM: $PARITY_INDEX"
# Map RAID device index to loop device
PARITY_DISK=$((10 + $PARITY_INDEX))
echo "Parity is on loop$PARITY_DISK"
echo
for i in {10..14}; do
# Read first byte from device
BYTE=$(read_first_byte /dev/loop$i $DATA_OFFSET)
BEFORE_BYTES[$i]=$BYTE
DISK_NAMES[$i]="loop$i"
echo -n "loop$i: 0x$BYTE"
if [ "$i" = "$PARITY_DISK" ]; then
echo " <-- PARITY disk"
else
echo
fi
done
echo
echo "4. Fail the first disk..."
dmsetup suspend disk0-flakey
dmsetup reload disk0-flakey --table "0 $SIZE flakey /dev/loop10 0 0 4294967295 2 error_reads error_writes"
dmsetup resume disk0-flakey
perl -e "print chr(4) x 32768" | dd of=$RAID_DEV bs=32k count=1 seek=2 oflag=direct status=none
sync
sleep 1
dmsetup suspend journal-flakey
dmsetup reload journal-flakey --table "0 $SIZE flakey /dev/loop15 0 0 4294967295 2 error_reads error_writes"
dmsetup resume journal-flakey
dmsetup suspend disk1-flakey
dmsetup reload disk1-flakey --table "0 $SIZE flakey /dev/loop11 0 0 4294967295 2 error_reads error_writes"
dmsetup resume disk1-flakey
echo "5. Attempting write (should fail the 2nd disk and the journal)..."
dd if=/dev/zero of=$RAID_DEV bs=32k count=1 seek=0 oflag=direct 2>&1 || echo "Write failed (expected)"
sync
sleep 1
echo
echo "6. Checking if parity was incorrectly updated:"
CHANGED=0
for i in {10..14}; do
# Read current state from device
BYTE_AFTER=$(read_first_byte /dev/loop$i $DATA_OFFSET)
BYTE_BEFORE=${BEFORE_BYTES[$i]}
if [ "$BYTE_BEFORE" != "$BYTE_AFTER" ]; then
echo "*** loop$i CHANGED: 0x$BYTE_BEFORE -> 0x$BYTE_AFTER ***"
CHANGED=$((CHANGED + 1))
if [ "$i" = "$PARITY_DISK" ]; then
echo " ^^ PARITY WAS UPDATED - BUG DETECTED!"
fi
else
echo "loop$i unchanged: 0x$BYTE_BEFORE"
fi
done
echo
echo "RESULT:"
if [ $CHANGED -gt 0 ]; then
echo "*** BUG DETECTED: $CHANGED disk(s) changed despite journal failure ***"
else
echo "✓ GOOD: No disks changed"
fi
cleanup
drivers/md/raid5.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 023649fe2476..da7756cc6a2a 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -1146,9 +1146,21 @@ static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
might_sleep();
+ /* Successfully logged to journal */
if (log_stripe(sh, s) == 0)
return;
+ /*
+ * Journal device failed. Only abort writes if we have
+ * too many failed devices to maintain consistency.
+ */
+ if (conf->log && r5l_log_disk_error(conf) &&
+ s->failed > conf->max_degraded &&
+ (s->to_write || s->written)) {
+ set_bit(STRIPE_HANDLE, &sh->state);
+ return;
+ }
+
should_defer = conf->batch_bio_dispatch && conf->group_cnt;
for (i = disks; i--; ) {
@@ -3672,6 +3684,13 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh,
* still be locked - so just clear all R5_LOCKED flags
*/
clear_bit(R5_LOCKED, &sh->dev[i].flags);
+ /* Clear R5_Want* flags to prevent stale operations
+ * from executing on retry.
+ */
+ clear_bit(R5_Wantwrite, &sh->dev[i].flags);
+ clear_bit(R5_Wantcompute, &sh->dev[i].flags);
+ clear_bit(R5_WantFUA, &sh->dev[i].flags);
+ clear_bit(R5_Wantdrain, &sh->dev[i].flags);
Still not sure about this, I need more time to go through each flag.
BTW, I'm not that familiar with raid5 internal details.
Thanks,
Kuai
}
s->to_write = 0;
s->written = 0;
.
