On Tue, Jun 30, 2026 at 05:18:42PM +0800, Gregory Price wrote: > Add a kselftest for the dax/kmem whole-device "state" sysfs attribute > (/sys/bus/dax/devices/daxX.Y/state), which transitions a kmem-backed > dax device between "unplugged", "online" and "online_movable". > > The kselftest also includes a test to demonstrate the force-unbind > does not deadlock - but this is a destructive test. The dax device > can never be rebound after doing this. > > Provisioning a devdax device and binding it to kmem needs daxctl/ndctl > out of scope for an in-tree selftest, so the test discovers an already > kmem-bound dax device and SKIPs when none are present or the memory > cannot be freed to reach a known baseline. > > When a device is available it validates the interface contract: > - online / online_movable actually add memory (MemTotal grows), > - online is idempotent, > - switching between online types without unplug is rejected, > - unplug removes memory and the reported state is "unplugged" > - invalid input is rejected. > > One specific regression test: > online -> unplug -> online_movable -> unplug > > Re-online must re-reserve per-range resources so subsequent unplug > actually offlines and removes instead of silently reporting success > while the memory stays online. > > Signed-off-by: Gregory Price <[email protected]> > --- > tools/testing/selftests/Makefile | 1 + > tools/testing/selftests/dax/Makefile | 6 + > tools/testing/selftests/dax/config | 4 + > .../testing/selftests/dax/dax-kmem-hotplug.sh | 190 ++++++++++++++++++ > tools/testing/selftests/dax/settings | 1 + > 5 files changed, 202 insertions(+) > create mode 100644 tools/testing/selftests/dax/Makefile > create mode 100644 tools/testing/selftests/dax/config > create mode 100755 tools/testing/selftests/dax/dax-kmem-hotplug.sh > create mode 100644 tools/testing/selftests/dax/settings > > diff --git a/tools/testing/selftests/Makefile > b/tools/testing/selftests/Makefile > index 6e59b8f63e41..8c2b4f97619c 100644 > --- a/tools/testing/selftests/Makefile > +++ b/tools/testing/selftests/Makefile > @@ -14,6 +14,7 @@ TARGETS += core > TARGETS += cpufreq > TARGETS += cpu-hotplug > TARGETS += damon > +TARGETS += dax > TARGETS += devices/error_logs > TARGETS += devices/probe > TARGETS += dmabuf-heaps > diff --git a/tools/testing/selftests/dax/Makefile > b/tools/testing/selftests/dax/Makefile > new file mode 100644 > index 000000000000..25a4f3d73a5b > --- /dev/null > +++ b/tools/testing/selftests/dax/Makefile > @@ -0,0 +1,6 @@ > +# SPDX-License-Identifier: GPL-2.0 > +all: > + > +TEST_PROGS := dax-kmem-hotplug.sh > + > +include ../lib.mk > diff --git a/tools/testing/selftests/dax/config > b/tools/testing/selftests/dax/config > new file mode 100644 > index 000000000000..4c9aaeb6ceb4 > --- /dev/null > +++ b/tools/testing/selftests/dax/config > @@ -0,0 +1,4 @@ > +CONFIG_DEV_DAX=m > +CONFIG_DEV_DAX_KMEM=m > +CONFIG_MEMORY_HOTPLUG=y > +CONFIG_MEMORY_HOTREMOVE=y > diff --git a/tools/testing/selftests/dax/dax-kmem-hotplug.sh > b/tools/testing/selftests/dax/dax-kmem-hotplug.sh > new file mode 100755 > index 000000000000..c8bbaf6178ed > --- /dev/null > +++ b/tools/testing/selftests/dax/dax-kmem-hotplug.sh > @@ -0,0 +1,190 @@ > +#!/bin/bash > +# SPDX-License-Identifier: GPL-2.0 > +# > +# Exercise the dax/kmem "state" sysfs attribute: > +# /sys/bus/dax/devices/daxX.Y/state -> unplugged | online | > online_kernel | online_movable > +# > +# The test needs a dax device already bound to the kmem driver. > +# If no suitable device is found the tests SKIP. > +# > +# A dax device can be provisioned with the memmap= boot param, e.g.: > +# memmap=2G!4G > +# > +# then, in the booted system: > +# > +# ndctl create-namespace -m devdax -e namespace0.0 -f > +# daxctl reconfigure-device -N -m system-ram dax0.0 # bind kmem > +# ./dax-kmem-hotplug.sh > + > +# shellcheck disable=SC1091 > +DIR="$(dirname "$(readlink -f "$0")")" > +. "$DIR"/../kselftest/ktap_helpers.sh > + > +DAX_BASE=/sys/bus/dax/devices > + > +memtotal_kb() { awk '/^MemTotal:/ {print $2}' /proc/meminfo; } > +get_state() { cat "$HP" 2>/dev/null; } > +# set_state STATE -- write a state to the state attribute; returns the > +# write's exit status (0 = accepted by the kernel) > +set_state() { echo "$1" > "$HP" 2>/dev/null; } > + > +find_kmem_dax() { > + local d drv > + for d in "$DAX_BASE"/dax*; do > + [ -e "$d/state" ] || continue > + drv=$(readlink "$d/driver" 2>/dev/null) > + [ "$(basename "${drv:-}")" = kmem ] || continue > + basename "$d" > + return 0 > + done > + return 1 > +}
It picks the first kmem-bound dax device and runs online/offline cycles on it. If the selected device is a real device with production usage, offlining movable memory will migrate all in-use pages. Could the destructive parts be gated behind an opt-in, e.g. an environment var ? Or find the testable backend device instead of just picking the first one? Best regards, Richard Cheng. > + > +ktap_print_header > + > +if [ "$UID" != 0 ]; then > + ktap_skip_all "must be run as root" > + exit "$KSFT_SKIP" > +fi > + > +DAX=$(find_kmem_dax) > +if [ -z "$DAX" ]; then > + ktap_skip_all "no kmem-bound dax device with a state attribute" > + exit "$KSFT_SKIP" > +fi > +HP=$DAX_BASE/$DAX/state > +ORIG=$(get_state) > + > +# A failure to reach the baseline is environmental (memory in use), not an > +# interface failure, so skip rather than fail. > +set_state unplugged; rc=$? > +if [ "$rc" != 0 ] || [ "$(get_state)" != unplugged ]; then > + ktap_skip_all "$DAX: cannot reach 'unplugged' baseline (memory in use?)" > + [ -n "$ORIG" ] && set_state "$ORIG" > + exit "$KSFT_SKIP" > +fi > +mt_unplugged=$(memtotal_kb) > + > +DRV=/sys/bus/dax/drivers/kmem > +AOB=/sys/devices/system/memory/auto_online_blocks > + > +ktap_print_msg "using $DAX (initial state was: $ORIG)" > +ktap_set_plan 8 > + > +# A public (N_MEMORY) kmem node onlined into a kernel zone > (online/online_kernel) > +# collects unmovable allocations and can then never be offlined, which would > +# wedge the device for the rest of this test. So this test only ever > +# successfully onlines online_movable, the one mode that is reliably > unpluggable. > + > +set_state online_movable; rc=$? > +mt_online=$(memtotal_kb) > +if [ "$rc" = 0 ] && [ "$(get_state)" = online_movable ] && [ "$mt_online" > -gt "$mt_unplugged" ]; then > + ktap_test_pass "online_movable: state=online_movable, MemTotal > $mt_unplugged -> $mt_online kB" > +else > + ktap_test_fail "online_movable: rc=$rc state=$(get_state) MemTotal > $mt_unplugged -> $mt_online" > +fi > + > +set_state online_movable; rc=$? > +if [ "$rc" = 0 ] && [ "$(get_state)" = online_movable ]; then > + ktap_test_pass "online_movable idempotent" > +else > + ktap_test_fail "online_movable idempotent: rc=$rc state=$(get_state)" > +fi > + > +# A different online type is rejected without an intervening unplug. The > write > +# is refused before any hotplug, so this never actually onlines a kernel > zone. > +set_state online_kernel; rc=$? > +if [ "$rc" != 0 ] && [ "$(get_state)" = online_movable ]; then > + ktap_test_pass "reject online_kernel without intervening unplug (no > kernel-zone online)" > +else > + ktap_test_fail "online_movable->online_kernel not rejected: rc=$rc > state=$(get_state)" > +fi > + > +set_state unplugged; rc=$? > +mt=$(memtotal_kb) > +if [ "$rc" = 0 ] && [ "$(get_state)" = unplugged ] && [ "$mt" -lt > "$mt_online" ]; then > + ktap_test_pass "unplug from online_movable: MemTotal $mt_online -> $mt > kB" > +else > + ktap_test_fail "unplug from online_movable: rc=$rc state=$(get_state) > MemTotal $mt_online -> $mt" > +fi > + > +before=$(get_state) > +set_state bogus_state; rc=$? > +if [ "$rc" != 0 ] && [ "$(get_state)" = "$before" ]; then > + ktap_test_pass "reject invalid state string" > +else > + ktap_test_fail "invalid state not rejected: rc=$rc state=$(get_state)" > +fi > + > +# The online_movable -> unplug cycle once regressed: a re-online failed to > +# re-reserve the per-range resources, so a later unplug reported success > while > +# leaving the memory online. Assert each iteration really adds and frees > memory. > +set_state unplugged > +cycle_ok=1; fail_i=0; on=0; off=0 > +for i in 1 2 3; do > + if ! set_state online_movable; then cycle_ok=0; fail_i=$i; break; fi > + on=$(memtotal_kb) > + if ! set_state unplugged; then cycle_ok=0; fail_i=$i; break; fi > + off=$(memtotal_kb) > + if [ "$on" -le "$mt_unplugged" ] || [ "$off" -ge "$on" ]; then > + cycle_ok=0; fail_i=$i; break > + fi > +done > +if [ "$cycle_ok" = 1 ]; then > + ktap_test_pass "online_movable/unplug cycle re-acquires resources (3x: > added and freed each time)" > +else > + ktap_test_fail "online_movable/unplug cycle regressed at iteration > $fail_i (on=$on off=$off baseline=$mt_unplugged)" > +fi > + > +# change system default online policy while the device is unbound, and show > +# the new system default policy is utilized across bindings. > +set_state unplugged > +if [ -w "$AOB" ] && [ -w "$DRV/unbind" ] && [ -w "$DRV/bind" ]; then > + orig_aob=$(cat "$AOB") > + echo "$DAX" > "$DRV/unbind" 2>/dev/null > + echo offline > "$AOB" 2>/dev/null > + echo "$DAX" > "$DRV/bind" 2>/dev/null > + sleep 1 > + st=$(get_state) > + echo "$orig_aob" > "$AOB" 2>/dev/null # restore system policy > + if [ "$st" = offline ]; then > + ktap_test_pass "online policy resolved at bind: > auto_online_blocks=offline -> state=offline" > + else > + ktap_test_fail "bind-time policy not honored: state=$st > (expected offline)" > + fi > + set_state unplugged 2>/dev/null > +else > + ktap_test_skip "auto_online_blocks or driver bind/unbind not writable" > +fi > + > +[ -n "$ORIG" ] && set_state "$ORIG" > + > +# DESTRUCTIVE: unbinding the driver while memory is online causes the > resources > +# to leak - but the unbind should not deadlock. Instead the driver leaks it > +# with a single "stuck online" warning. This leaves the memory online and the > +# device unbound until reboot, so it runs last - and only if we can run it, > +# leaving the restored state above untouched otherwise. online_movable only: > +# this test never onlines a public node into a kernel zone. > +if [ -w "$DRV/unbind" ]; then > + set_state unplugged; set_state online_movable > +fi > +if [ "$(get_state)" = online_movable ] && [ -w "$DRV/unbind" ]; then > + mt_on=$(memtotal_kb) > + dmesg -C 2>/dev/null > + echo "$DAX" > "$DRV/unbind" 2>/dev/null > + mt_after=$(memtotal_kb) > + # The leaked "System RAM (kmem)" regions stay in the iomem tree; reading > + # their names dereferences res_name, which a buggy unbind already freed. > + # Walk /proc/iomem to provoke that use-after-free (caught by KASAN). > + cat /proc/iomem > /dev/null 2>&1 > + splat=$(dmesg 2>/dev/null | grep -ciE > "KASAN|BUG:|use-after-free|general protection|Oops|refcount_t") > + if [ "$splat" = 0 ] && [ "$mt_after" -ge "$mt_on" ]; then > + ktap_test_pass "unbind while online: memory left online, no > UAF/oops (MemTotal $mt_on -> $mt_after kB)" > + else > + ktap_test_fail "unbind while online regressed: splat=$splat > MemTotal $mt_on -> $mt_after kB" > + fi > +else > + ktap_test_skip "could not online device for unbind-while-online test" > +fi > + > +ktap_finished > diff --git a/tools/testing/selftests/dax/settings > b/tools/testing/selftests/dax/settings > new file mode 100644 > index 000000000000..ba4d85f74cd6 > --- /dev/null > +++ b/tools/testing/selftests/dax/settings > @@ -0,0 +1 @@ > +timeout=90 > -- > 2.53.0-Meta > >
