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J . Bottomley" , "Martin K . Petersen" Cc: ahuang12@lenovo.com, axboe@kernel.dk, damien.lemoal@opensource.wdc.com, hch@lst.de, iommu@lists.linux.dev, ionut_n2001@yahoo.com, john.g.garry@oracle.com, kbusch@kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org, m.szyprowski@samsung.com, robin.murphy@arm.com, sagi@grimberg.me, stable@vger.kernel.org, sunlightlinux@gmail.com, Ionut Nechita Subject: [PATCH 1/1] scsi: sas: skip opt_sectors when DMA reports no real optimization hint Date: Wed, 18 Mar 2026 09:43:14 +0200 Message-ID: <20260318074314.17372-2-ionut.nechita@windriver.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260318074314.17372-1-ionut.nechita@windriver.com> References: <20260318074314.17372-1-ionut.nechita@windriver.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: BE0P281CA0034.DEUP281.PROD.OUTLOOK.COM (2603:10a6:b10:14::21) To SJ2PR11MB7546.namprd11.prod.outlook.com (2603:10b6:a03:4cc::8) 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priorityscore=1501 adultscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603180063 From: Ionut Nechita sas_host_setup() unconditionally sets shost->opt_sectors from dma_opt_mapping_size(). When the IOMMU is disabled or in passthrough mode and no DMA ops provide an opt_mapping_size callback, dma_opt_mapping_size() returns min(dma_max_mapping_size(), SIZE_MAX) which equals dma_max_mapping_size() =E2=80=94 a hard upper bound, not an optimization hint. On a Dell PowerEdge R750 with mpt3sas (Broadcom SAS3816, FW 33.15.00.00) and intel_iommu=3Doff the following values are observed: dma_opt_mapping_size() =3D dma_max_mapping_size() (no real hint) shost->max_sectors =3D 32767 opt_sectors =3D min(32767, huge >> 9) =3D 32767 optimal_io_size =3D 32767 << 9 =3D 16776704 =E2=86=92 round_down(16776704, 4096) =3D 16773120 The SAS disk (SAMSUNG MZILT800HBHQ0D3) do not report an Optimal Transfer Length in VPD page B0,so sdkp->opt_xfer_blocks remains 0. sd_revalidate_disk() then uses min_not_zero(0, opt_sectors) =3D opt_sectors, propagating the bogus value into the block device's optimal_io_size (visible as OPT-IO =3D 16773120 in lsblk --topology). mkfs.xfs picks up optimal_io_size and minimum_io_size and computes: swidth =3D 16773120 / 4096 =3D 4095 sunit =3D 8192 / 4096 =3D 2 Since 4095 % 2 !=3D 0, XFS rejects the geometry: SB stripe unit sanity check failed This makes it impossible to create XFS filesystems (e.g. for /var/lib/docker) during system bootstrap. Fix this by only setting opt_sectors when dma_opt_mapping_size() returns a value strictly less than dma_max_mapping_size(), which indicates a genuine DMA optimization constraint from an IOMMU or DMA ops backend. When they are equal, no backend provided a real hint, so leave opt_sectors at its default of 0 ("no preference"). Fixes: 4cbfca5f7750 ("scsi: scsi_transport_sas: cap shost opt_sectors accor= ding to DMA optimal limit") Cc: stable@vger.kernel.org Signed-off-by: Ionut Nechita --- drivers/scsi/scsi_transport_sas.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/drivers/scsi/scsi_transport_sas.c b/drivers/scsi/scsi_transpor= t_sas.c index 12124f9d5ccd..6b4de5116feb 100644 --- a/drivers/scsi/scsi_transport_sas.c +++ b/drivers/scsi/scsi_transport_sas.c @@ -240,8 +240,20 @@ static int sas_host_setup(struct transport_container *= tc, struct device *dev, shost->host_no); =20 if (dma_dev->dma_mask) { - shost->opt_sectors =3D min_t(unsigned int, shost->max_sectors, - dma_opt_mapping_size(dma_dev) >> SECTOR_SHIFT); + size_t opt =3D dma_opt_mapping_size(dma_dev); + + /* + * Only set opt_sectors when the DMA layer reports a + * genuine optimization constraint. When opt equals + * dma_max_mapping_size() no backend provided a real + * hint =E2=80=94 the value is just the DMA maximum, which is + * not useful as an optimal I/O size and can cause + * mkfs.xfs to compute invalid stripe geometry. + */ + if (opt < dma_max_mapping_size(dma_dev)) + shost->opt_sectors =3D min_t(unsigned int, + shost->max_sectors, + opt >> SECTOR_SHIFT); } =20 return 0; --=20 2.53.0