When revalidating a zoned SCSI disk, we need to do a REPORT ZONES, which
also updates the write-pointer offset cache.
As we don't want a normal REPORT ZONES to constantly update the
write-pointer offset cache, we swap the cache contents from revalidate
with the live version.
But if a second REPORT ZONES is triggered while '->rev_wp_offset' is
already allocated, sd_zbc_parse_report() can't distinguish the two
different REPORT ZONES (from revalidation context or from a
file-system/ioctl).
CPU0 CPU1
sd_zbc_revalidate_zones()
`-> mutex_lock(&sdkp->rev_mutex);
`-> sdkp->rev_wp_offset = kvcalloc();
`->blk_revalidate_disk_zones();
`-> disk->fops->report_zones();
`-> sd_zbc_report_zones();
`-> sd_zbc_parse_report();
`-> if (sdkp->rev_wp_offset)
`-> sdkp->rev_wp_offset[idx] =
blkdev_report_zones()
`-> disk->fops->report_zones();
`-> sd_zbc_report_zones();
`-> sd_zbc_parse_report();
`-> if (sdkp->rev_wp_offset)
`-> sdkp->rev_wp_offset[idx] =
`-> update_driver_data();
`-> sd_zbc_revalidate_zones_cb();
`-> swap(sdkp->zones_wp_offset, sdkp->rev_wp_offset);
`-> kvfree(sdkp->rev_wp_offset);
`-> sdkp->rev_wp_offset = NULL;
`-> mutex_unlock(&sdkp->rev_mutex);
As two concurrent revalidates are excluded via the '->rev_mutex', try to
grab the '->rev_mutex' in sd_zbc_report_zones(). If we cannot lock the
'->rev_mutex' because it's already held, we know we're called in a disk
revalidate context, if we can grab the mutex we need to unlock it again
after sd_zbc_parse_report() as we're not called in a revalidate context.
This way we can ensure a partial REPORT ZONES doesn't set invalid
write-pointer offsets in the revalidate write-pointer offset cache when a
partial REPORT ZONES is running concurrently with a full REPORT ZONES from
disk revalidation.
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
---
drivers/scsi/sd_zbc.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/drivers/scsi/sd_zbc.c b/drivers/scsi/sd_zbc.c
index 6f7eba66687e..d19456220c09 100644
--- a/drivers/scsi/sd_zbc.c
+++ b/drivers/scsi/sd_zbc.c
@@ -198,6 +198,7 @@ int sd_zbc_report_zones(struct gendisk *disk, sector_t sector,
unsigned char *buf;
size_t offset, buflen = 0;
int zone_idx = 0;
+ bool unlock = false;
int ret;
if (!sd_is_zoned(sdkp))
@@ -223,6 +224,14 @@ int sd_zbc_report_zones(struct gendisk *disk, sector_t sector,
if (!nr)
break;
+ /*
+ * Check if we're called by revalidate or by a normal report
+ * zones. Mutually exclude report zones due to revalidation and
+ * normal report zones, so we're not accidentally overriding the
+ * write-pointer offset cache.
+ */
+ if (mutex_trylock(&sdkp->rev_mutex))
+ unlock = true;
for (i = 0; i < nr && zone_idx < nr_zones; i++) {
offset += 64;
ret = sd_zbc_parse_report(sdkp, buf + offset, zone_idx,
@@ -231,6 +240,8 @@ int sd_zbc_report_zones(struct gendisk *disk, sector_t sector,
goto out;
zone_idx++;
}
+ if (unlock)
+ mutex_unlock(&sdkp->rev_mutex);
sector += sd_zbc_zone_sectors(sdkp) * i;
}
--
2.26.2
