Kolbjørn and Jonáš reported that their 32-bit PowerMacs were crashing
in pata-macio since commit 09fe2bfa6b83 ("ata: pata_macio: Fix
max_segment_size with PAGE_SIZE == 64K").
For example:
kernel BUG at drivers/ata/pata_macio.c:544!
Oops: Exception in kernel mode, sig: 5 [#1]
BE PAGE_SIZE=4K MMU=Hash SMP NR_CPUS=2 DEBUG_PAGEALLOC PowerMac
...
NIP pata_macio_qc_prep+0xf4/0x190
LR pata_macio_qc_prep+0xfc/0x190
Call Trace:
0xc1421660 (unreliable)
ata_qc_issue+0x14c/0x2d4
__ata_scsi_queuecmd+0x200/0x53c
ata_scsi_queuecmd+0x50/0xe0
scsi_queue_rq+0x788/0xb1c
__blk_mq_issue_directly+0x58/0xf4
blk_mq_plug_issue_direct+0x8c/0x1b4
blk_mq_flush_plug_list.part.0+0x584/0x5e0
__blk_flush_plug+0xf8/0x194
__submit_bio+0x1b8/0x2e0
submit_bio_noacct_nocheck+0x230/0x304
btrfs_work_helper+0x200/0x338
process_one_work+0x1a8/0x338
worker_thread+0x364/0x4c0
kthread+0x100/0x104
start_kernel_thread+0x10/0x14
That commit increased max_segment_size to 64KB, with the justification
that the SCSI core was already using that size when PAGE_SIZE == 64KB,
and that there was existing logic to split over-sized requests.
However with a sufficiently large request, the splitting logic causes
each sg to be split into two commands in the DMA table, leading to
overflow of the DMA table, triggering the BUG_ON().
With default settings the bug doesn't trigger, because the request size
is limited by max_sectors_kb == 1280, however max_sectors_kb can be
increased, and apparently some distros do that by default using udev
rules.
Fix the bug for 4KB kernels by reverting to the old max_segment_size.
For 64KB kernels the sg_tablesize needs to be halved, to allow for the
possibility that each sg will be split into two.
Fixes: 09fe2bfa6b83 ("ata: pata_macio: Fix max_segment_size with PAGE_SIZE == 64K")
Cc: stable@xxxxxxxxxxxxxxx # v6.10+
Reported-by: Kolbjørn Barmen <linux-ppc@xxxxxxxx>
Closes: https://lore.kernel.org/all/62d248bb-e97a-25d2-bcf2-9160c518cae5@xxxxxxxx/
Reported-by: Jonáš Vidra <vidra@xxxxxxxxxxxxxxxx>
Closes: https://lore.kernel.org/all/3b6441b8-06e6-45da-9e55-f92f2c86933e@xxxxxxxxxxxxxxxx/
Tested-by: Kolbjørn Barmen <linux-ppc@xxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
---
drivers/ata/pata_macio.c | 23 +++++++++++++++--------
1 file changed, 15 insertions(+), 8 deletions(-)
diff --git a/drivers/ata/pata_macio.c b/drivers/ata/pata_macio.c
index 1b85e8bf4ef9..eaffa510de49 100644
--- a/drivers/ata/pata_macio.c
+++ b/drivers/ata/pata_macio.c
@@ -208,6 +208,19 @@ static const char* macio_ata_names[] = {
/* Don't let a DMA segment go all the way to 64K */
#define MAX_DBDMA_SEG 0xff00
+#ifdef CONFIG_PAGE_SIZE_64KB
+/*
+ * The SCSI core requires the segment size to cover at least a page, so
+ * for 64K page size kernels it must be at least 64K. However the
+ * hardware can't handle 64K, so pata_macio_qc_prep() will split large
+ * requests. To handle the split requests the tablesize must be halved.
+ */
+#define MAX_SEGMENT_SIZE SZ_64K
+#define SG_TABLESIZE (MAX_DCMDS / 2)
+#else
+#define MAX_SEGMENT_SIZE MAX_DBDMA_SEG
+#define SG_TABLESIZE MAX_DCMDS
+#endif
/*
* Wait 1s for disk to answer on IDE bus after a hard reset
@@ -912,16 +925,10 @@ static int pata_macio_do_resume(struct pata_macio_priv *priv)
static const struct scsi_host_template pata_macio_sht = {
__ATA_BASE_SHT(DRV_NAME),
- .sg_tablesize = MAX_DCMDS,
+ .sg_tablesize = SG_TABLESIZE,
/* We may not need that strict one */
.dma_boundary = ATA_DMA_BOUNDARY,
- /*
- * The SCSI core requires the segment size to cover at least a page, so
- * for 64K page size kernels this must be at least 64K. However the
- * hardware can't handle 64K, so pata_macio_qc_prep() will split large
- * requests.
- */
- .max_segment_size = SZ_64K,
+ .max_segment_size = MAX_SEGMENT_SIZE,
.device_configure = pata_macio_device_configure,
.sdev_groups = ata_common_sdev_groups,
.can_queue = ATA_DEF_QUEUE,
--
2.46.0
