From: Niklas Cassel <cassel@kernel.org> mainline inclusion from mainline-v7.1-rc1 commit f233124fb36cd57ef09f96d517a38ab4b902e15e category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15109 CVE: CVE-2026-45855 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- When using Port Multipliers (PMPs) with Command-Based Switching (CBS), you can only issue commands to one link at a time. For PMPs with CBS, there is already code to handle commands being sent to different links in sata_pmp_qc_defer_cmd_switch() using ap->excl_link. sata_sil24 also makes use of ap->excl_link. A user on the list reported that commit 0ea84089dbf6 ("ata: libata-scsi: avoid Non-NCQ command starvation") broke PMPs with CBS. The commit introduced code that stores a deferred qc in ap->deferred_qc, to later be issued via a workqueue. It turns out that this change is incompatible with the existing ap->excl_link handling used by PMPs with CBS. Thus, modify sata_pmp_qc_defer_cmd_switch() and sil24_qc_defer() to return ATA_DEFER_LINK_EXCL, and make sure that the deferred QC handling via workqueue is not used for this return value. This way, PMPs with CBS will work once again. Note that the starvation referenced in commit 0ea84089dbf6 ("ata: libata-scsi: avoid Non-NCQ command starvation") can only happen on libsas ports, and libsas does not support Port Multipliers, thus there is no harm of reverting back to the previous way of deferring commands for PMPs with CBS. Non-libsas ports connected to anything but a PMP with CBS (e.g. a normal drive or a PMP with FBS) will continue using the deferred workqueue, since it does result in lower completion latencies for non-NCQ commands, even though the workqueue is not strictly needed to avoid starvation for non-libsas ports. If we want to modify the scope of the workqueue issuing to also handle PMPs with CBS, then we should ensure that we can save both NCQ and non-NCQ commands in ap->deferred_qc, while also removing the existing PMP CBS handling using ap->excl_link, such that we don't duplicate features. While at it, also add a comment explaining how the ap->excl_link mechanism works. Fixes: 0ea84089dbf6 ("ata: libata-scsi: avoid Non-NCQ command starvation") Tested-by: Tommy Kelly <linux@tkel.ly> Reported-by: Tommy Kelly <linux@tkel.ly> Closes: https://lore.kernel.org/linux-ide/ce09cc21-a8e9-4845-b205-35411e22fba9@tkel.... Reviewed-by: Damien Le Moal <dlemoal@kernel.org> Signed-off-by: Niklas Cassel <cassel@kernel.org> Signed-off-by: Long Li <leo.lilong@huawei.com> --- drivers/ata/libata-pmp.c | 13 ++++++++++++- drivers/ata/libata-scsi.c | 8 ++++++++ drivers/ata/sata_sil24.c | 6 +++++- include/linux/libata.h | 1 + 4 files changed, 26 insertions(+), 2 deletions(-) diff --git a/drivers/ata/libata-pmp.c b/drivers/ata/libata-pmp.c index e2e9cbd405fa..7a54df99fade 100644 --- a/drivers/ata/libata-pmp.c +++ b/drivers/ata/libata-pmp.c @@ -110,13 +110,24 @@ int sata_pmp_qc_defer_cmd_switch(struct ata_queued_cmd *qc) { struct ata_link *link = qc->dev->link; struct ata_port *ap = link->ap; + int ret; if (ap->excl_link == NULL || ap->excl_link == link) { if (ap->nr_active_links == 0 || ata_link_active(link)) { qc->flags |= ATA_QCFLAG_CLEAR_EXCL; - return ata_std_qc_defer(qc); + ret = ata_std_qc_defer(qc); + if (ret == ATA_DEFER_LINK) + return ATA_DEFER_LINK_EXCL; + return ret; } + /* + * Note: ap->excl_link contains the link that is next in line, + * i.e. implicit round robin. If there is only one link + * dispatching, ap->excl_link will be left unclaimed, allowing + * other links to set ap->excl_link, ensuring that the currently + * active link cannot queue any more. + */ ap->excl_link = link; } diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c index 4a66b17d9f8d..f14c827974bc 100644 --- a/drivers/ata/libata-scsi.c +++ b/drivers/ata/libata-scsi.c @@ -1831,6 +1831,14 @@ static int ata_scsi_qc_issue(struct ata_port *ap, struct ata_queued_cmd *qc) case ATA_DEFER_LINK: ret = SCSI_MLQUEUE_DEVICE_BUSY; goto defer_qc; + case ATA_DEFER_LINK_EXCL: + /* + * Drivers making use of ap->excl_link cannot store the QC in + * ap->deferred_qc, because the ap->excl_link handling is + * incompatible with the ap->deferred_qc workqueue handling. + */ + ret = SCSI_MLQUEUE_DEVICE_BUSY; + goto free_qc; case ATA_DEFER_PORT: ret = SCSI_MLQUEUE_HOST_BUSY; goto free_qc; diff --git a/drivers/ata/sata_sil24.c b/drivers/ata/sata_sil24.c index 142e70bfc498..aee4642125e8 100644 --- a/drivers/ata/sata_sil24.c +++ b/drivers/ata/sata_sil24.c @@ -790,6 +790,7 @@ static int sil24_qc_defer(struct ata_queued_cmd *qc) struct ata_link *link = qc->dev->link; struct ata_port *ap = link->ap; u8 prot = qc->tf.protocol; + int ret; /* * There is a bug in the chip: @@ -827,7 +828,10 @@ static int sil24_qc_defer(struct ata_queued_cmd *qc) qc->flags |= ATA_QCFLAG_CLEAR_EXCL; } - return ata_std_qc_defer(qc); + ret = ata_std_qc_defer(qc); + if (ret == ATA_DEFER_LINK) + return ATA_DEFER_LINK_EXCL; + return ret; } static enum ata_completion_errors sil24_qc_prep(struct ata_queued_cmd *qc) diff --git a/include/linux/libata.h b/include/linux/libata.h index a4fa7ad43077..1e25b8735ce8 100644 --- a/include/linux/libata.h +++ b/include/linux/libata.h @@ -309,6 +309,7 @@ enum { /* return values for ->qc_defer */ ATA_DEFER_LINK = 1, ATA_DEFER_PORT = 2, + ATA_DEFER_LINK_EXCL = 3, /* desc_len for ata_eh_info and context */ ATA_EH_DESC_LEN = 80, -- 2.52.0