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authorRyan Kuester <rkuester@kspace.net>2010-04-26 18:11:54 -0500
committerWilly Tarreau <w@1wt.eu>2011-04-30 16:53:40 +0200
commitffe4a23cef7aedc6747f1f092d26dcee941609bd (patch)
treeeaf3be3df47a7b935dcd975297b38beef038e7a2
parent36493e838ff016f2cd54353e81e9213d95c5022f (diff)
mptsas: fix hangs caused by ATA pass-through
commit 2a1b7e575b80ceb19ea50bfa86ce0053ea57181d upstream. I may have an explanation for the LSI 1068 HBA hangs provoked by ATA pass-through commands, in particular by smartctl. First, my version of the symptoms. On an LSI SAS1068E B3 HBA running 01.29.00.00 firmware, with SATA disks, and with smartd running, I'm seeing occasional task, bus, and host resets, some of which lead to hard faults of the HBA requiring a reboot. Abusively looping the smartctl command, # while true; do smartctl -a /dev/sdb > /dev/null; done dramatically increases the frequency of these failures to nearly one per minute. A high IO load through the HBA while looping smartctl seems to improve the chance of a full scsi host reset or a non-recoverable hang. I reduced what smartctl was doing down to a simple test case which causes the hang with a single IO when pointed at the sd interface. See the code at the bottom of this e-mail. It uses an SG_IO ioctl to issue a single pass-through ATA identify device command. If the buffer userspace gives for the read data has certain alignments, the task is issued to the HBA but the HBA fails to respond. If run against the sg interface, neither the test code nor smartctl causes a hang. sd and sg handle the SG_IO ioctl slightly differently. Unless you specifically set a flag to do direct IO, sg passes a buffer of its own, which is page-aligned, to the block layer and later copies the result into the userspace buffer regardless of its alignment. sd, on the other hand, always does direct IO unless the userspace buffer fails an alignment test at block/blk-map.c line 57, in which case a page-aligned buffer is created and used for the transfer. The alignment test currently checks for word-alignment, the default setup by scsi_lib.c; therefore, userspace buffers of almost any alignment are given directly to the HBA as DMA targets. The LSI 1068 hardware doesn't seem to like at least a couple of the alignments which cross a page boundary (see the test code below). Curiously, many page-boundary-crossing alignments do work just fine. So, either the hardware has an bug handling certain alignments or the hardware has a stricter alignment requirement than the driver is advertising. If stricter alignment is required, then in no case should misaligned buffers from userspace be allowed through without being bounced or at least causing an error to be returned. It seems the mptsas driver could use blk_queue_dma_alignment() to advertise a stricter alignment requirement. If it does, sd does the right thing and bounces misaligned buffers (see block/blk-map.c line 57). The following patch to 2.6.34-rc5 makes my symptoms go away. I'm sure this is the wrong place for this code, but it gets my idea across. Acked-by: "Desai Kashyap" <Kashyap.Desai@lsi.com> Signed-off-by: James Bottomley <James.Bottomley@suse.de>
-rw-r--r--drivers/message/fusion/mptscsih.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/drivers/message/fusion/mptscsih.c b/drivers/message/fusion/mptscsih.c
index 9f9354fd3516..3e8c5383ecfe 100644
--- a/drivers/message/fusion/mptscsih.c
+++ b/drivers/message/fusion/mptscsih.c
@@ -2469,6 +2469,8 @@ mptscsih_slave_configure(struct scsi_device *sdev)
ioc->name,sdev->tagged_supported, sdev->simple_tags,
sdev->ordered_tags));
+ blk_queue_dma_alignment (sdev->request_queue, 512 - 1);
+
return 0;
}