From e0cb40c3c676786c92ddb7f891a928ce970d6244 Mon Sep 17 00:00:00 2001 From: John Groves Date: Mon, 15 Jun 2026 16:06:32 +0000 Subject: [PATCH] dax/fsdev: fix multi-range offset in memory_failure handler Fix memory_failure offset calculation for multi-range devices. The old code subtracted ranges[0].range.start from the faulting PFN's physical address, which produces an incorrect (inflated) logical offset when the PFN falls in ranges[1] or beyond due to physical gaps between ranges. Add fsdev_pfn_to_offset() to walk the range list and compute the correct device-linear byte offset relative to ranges[0].start (the device data start) -- the base the holder (xfs, famfs) maps from -- for both static and dynamic devices. V5 walked the pagemap's immutable pgmap->ranges[] instead, to avoid reading the mutable dev_dax->ranges[] from this callback. That had a different problem: it regressed static devices, where pgmap->ranges[0].start can sit data_offset below the data start, so the reported offset came out data_offset too high and the holder would act on the wrong blocks. For dynamic devices the two arrays are identical, so pgmap->ranges[] only ever helped the dynamic case while breaking the static one. Walk dev_dax->ranges[] instead. (Richard Cheng spotted the static regression.) Reading dev_dax->ranges[] here may race a concurrent krealloc() of the range array via sysfs (mapping_store(), under dax_region_rwsem, which this ->memory_failure callback does not hold). That exposure is pre-existing -- the original single-range code read dev_dax->ranges[0] locklessly as well -- so this patch does not make it worse; a proper fix (locking or snapshotting) belongs in a separate change. Fixes: d5406bd458b0a ("dax: add fsdev.c driver for fs-dax on character dax") Reviewed-by: Dave Jiang Reviewed-by: Alison Schofield Signed-off-by: John Groves Reviewed-by: Richard Cheng Link: https://patch.msgid.link/0100019ecc08d74f-ec0d09b8-11e9-4e5b-af48-8c6d382af486-000000@email.amazonses.com Signed-off-by: Alison Schofield --- drivers/dax/fsdev.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/drivers/dax/fsdev.c b/drivers/dax/fsdev.c index 188b2526bee4..f315533b299e 100644 --- a/drivers/dax/fsdev.c +++ b/drivers/dax/fsdev.c @@ -135,11 +135,26 @@ static void fsdev_clear_ops(void *data) * The core mm code in free_zone_device_folio() handles the wake_up_var() * directly for this memory type. */ +static u64 fsdev_pfn_to_offset(struct dev_dax *dev_dax, unsigned long pfn) +{ + phys_addr_t phys = PFN_PHYS(pfn); + u64 offset = 0; + + for (int i = 0; i < dev_dax->nr_range; i++) { + struct range *range = &dev_dax->ranges[i].range; + + if (phys >= range->start && phys <= range->end) + return offset + (phys - range->start); + offset += range_len(range); + } + return -1ULL; +} + static int fsdev_pagemap_memory_failure(struct dev_pagemap *pgmap, unsigned long pfn, unsigned long nr_pages, int mf_flags) { struct dev_dax *dev_dax = pgmap->owner; - u64 offset = PFN_PHYS(pfn) - dev_dax->ranges[0].range.start; + u64 offset = fsdev_pfn_to_offset(dev_dax, pfn); u64 len = nr_pages << PAGE_SHIFT; return dax_holder_notify_failure(dev_dax->dax_dev, offset,