On Wed, 18 Mar 2026 22:48:30 -0700 Alison Schofield <[email protected]> wrote:
> On Thu, Mar 19, 2026 at 01:14:56AM +0000, Smita Koralahalli wrote: > > From: Dan Williams <[email protected]> > > > > Move hmem/ earlier in the dax Makefile so that hmem_init() runs before > > dax_cxl. > > > > In addition, defer registration of the dax_cxl driver to a workqueue > > instead of using module_cxl_driver(). This ensures that dax_hmem has > > an opportunity to initialize and register its deferred callback and make > > ownership decisions before dax_cxl begins probing and claiming Soft > > Reserved ranges. > > > > Mark the dax_cxl driver as PROBE_PREFER_ASYNCHRONOUS so its probe runs > > out of line from other synchronous probing avoiding ordering > > dependencies while coordinating ownership decisions with dax_hmem. > > Hi Smita, > > Replying to this patch, as it's my best guess as to why I may be > seeing this WARN when I modprobe cxl-test. Not patch 6? dax_hmem_flush_work() is in there + it doesn't use a static declaration of the work items. I've not figure out the path yet but it looks more suspicious to me than this path. Jonathan > > We are able to pass all the CXL unit tests because it is only that > first load that causes the WARN. All subsequent reloads of cxl-test > do not unload dax_cxl and dax_hmem so they chug happily along. > > I can reproduce by unloading each piece before reloading cxl-test > # modprobe -r cxl-test > # modprobe -r dax_cxl > # modprobe -r dax_hmem > # modprobe cxl-test > and the WARN repeats. > > Guessing you may recognize what is going on. Let me know if I can > try anything else out. > > > # dmesg (trimmed to just the init calls) > [ 34.229033] calling fwctl_init+0x0/0xff0 [fwctl] @ 1057 > [ 34.230616] initcall fwctl_init+0x0/0xff0 [fwctl] returned 0 after 186 > usecs > [ 34.257096] calling cxl_core_init+0x0/0x100 [cxl_core] @ 1057 > [ 34.258395] initcall cxl_core_init+0x0/0x100 [cxl_core] returned 0 after > 538 usecs > [ 34.264170] calling cxl_port_init+0x0/0xff0 [cxl_port] @ 1057 > [ 34.264982] initcall cxl_port_init+0x0/0xff0 [cxl_port] returned 0 after > 110 usecs > [ 34.268058] calling cxl_mem_driver_init+0x0/0xff0 [cxl_mem] @ 1057 > [ 34.268743] initcall cxl_mem_driver_init+0x0/0xff0 [cxl_mem] returned 0 > after 110 usecs > [ 34.274670] calling cxl_pmem_init+0x0/0xff0 [cxl_pmem] @ 1057 > [ 34.277835] initcall cxl_pmem_init+0x0/0xff0 [cxl_pmem] returned 0 after > 1671 usecs > [ 34.285807] calling cxl_acpi_init+0x0/0xff0 [cxl_acpi] @ 1057 > [ 34.287105] initcall cxl_acpi_init+0x0/0xff0 [cxl_acpi] returned 0 after > 262 usecs > [ 34.292967] calling cxl_test_init+0x0/0xff0 [cxl_test] @ 1057 > [ 34.339841] initcall cxl_test_init+0x0/0xff0 [cxl_test] returned 0 after > 45832 usecs > [ 34.342259] calling cxl_mock_mem_driver_init+0x0/0xff0 [cxl_mock_mem] @ > 1063 > [ 34.343459] initcall cxl_mock_mem_driver_init+0x0/0xff0 [cxl_mock_mem] > returned 0 after 356 usecs > [ 34.658602] calling dax_hmem_init+0x0/0xff0 [dax_hmem] @ 1059 > [ 34.670106] calling cxl_pci_driver_init+0x0/0xff0 [cxl_pci] @ 1100 > [ 34.671023] initcall cxl_pci_driver_init+0x0/0xff0 [cxl_pci] returned 0 > after 197 usecs > [ 34.673051] initcall dax_hmem_init+0x0/0xff0 [dax_hmem] returned 0 after > 2225 usecs > [ 34.676011] calling cxl_dax_region_init+0x0/0xff0 [dax_cxl] @ 1059 > [ 34.676856] ------------[ cut here ]------------ > [ 34.677533] WARNING: kernel/workqueue.c:4289 at __flush_work+0x4f9/0x550, > CPU#3: kworker/3:2/136 > [ 34.678596] Modules linked in: dax_cxl(+) cxl_pci dax_hmem cxl_mock_mem(O) > cxl_test(O) cxl_acpi(O) cxl_pmem(O) cxl_mem(O) cxl_port(O) cxl_mock(O) > cxl_core(O) fwctl nd_pmem nd_btt dax_pmem nfit nd_e820 libnvdimm > [ 34.680632] initcall cxl_dax_region_init+0x0/0xff0 [dax_cxl] returned 0 > after 3842 usecs > [ 34.680918] CPU: 3 UID: 0 PID: 136 Comm: kworker/3:2 Tainted: G > O 7.0.0-rc4+ #156 PREEMPT(full) > [ 34.684368] Tainted: [O]=OOT_MODULE > [ 34.684993] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 > 02/06/2015 > [ 34.686098] Workqueue: events_long cxl_dax_region_driver_register [dax_cxl] > [ 34.687108] RIP: 0010:__flush_work+0x4f9/0x550 > > That addr is this line in flush_work() > if (WARN_ON(!work->func)) > return false; > > > [ 34.687811] Code: ff 49 8b 45 00 49 8b 55 08 89 c7 48 c1 e8 04 83 e7 08 83 > e0 0f 83 cf 02 49 0f ba 6d 00 03 e9 a1 fc ff ff 0f 0b e9 e6 fe ff ff <0f> 0b > e9 df fe ff ff e8 9b 48 15 01 85 c0 0f 84 26 ff ff ff 80 3d > [ 34.690107] RSP: 0018:ffffc900020b7cf8 EFLAGS: 00010246 > [ 34.690673] RAX: 0000000000000000 RBX: ffffffffa0ea2088 RCX: > ffff8880088b2b78 > [ 34.691388] RDX: 00000000834fb194 RSI: 0000000000000000 RDI: > ffffffffa0ea2088 > [ 34.692135] RBP: ffffc900020b7de0 R08: 0000000031ab93b0 R09: > 00000000effb42e8 > [ 34.692876] R10: 000000008effb42e R11: 0000000000000000 R12: > ffff88807d9bb340 > [ 34.693588] R13: ffffffffa0ea2088 R14: ffffffffa0ed2020 R15: > 0000000000000001 > [ 34.694358] FS: 0000000000000000(0000) GS:ffff8880fa45f000(0000) > knlGS:0000000000000000 > [ 34.695179] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 34.695775] CR2: 00007fe888b4e34c CR3: 00000000090ed004 CR4: > 0000000000370ef0 > [ 34.696494] Call Trace: > [ 34.696889] <TASK> > [ 34.697238] ? __lock_acquire+0xb08/0x2930 > [ 34.697730] ? __this_cpu_preempt_check+0x13/0x20 > [ 34.698277] flush_work+0x17/0x30 > [ 34.698705] dax_hmem_flush_work+0x10/0x20 [dax_hmem] > [ 34.699270] cxl_dax_region_driver_register+0x9/0x30 [dax_cxl] > [ 34.699943] process_one_work+0x203/0x6c0 > [ 34.700452] worker_thread+0x197/0x350 > [ 34.700942] ? __pfx_worker_thread+0x10/0x10 > [ 34.701455] kthread+0x108/0x140 > [ 34.701915] ? __pfx_kthread+0x10/0x10 > [ 34.702396] ret_from_fork+0x28a/0x310 > [ 34.702880] ? __pfx_kthread+0x10/0x10 > [ 34.703363] ret_from_fork_asm+0x1a/0x30 > [ 34.703872] </TASK> > [ 34.704227] irq event stamp: 11015 > [ 34.704656] hardirqs last enabled at (11025): [<ffffffff813486de>] > __up_console_sem+0x5e/0x80 > [ 34.705493] hardirqs last disabled at (11036): [<ffffffff813486c3>] > __up_console_sem+0x43/0x80 > [ 34.706354] softirqs last enabled at (10500): [<ffffffff812ab9f3>] > __irq_exit_rcu+0xc3/0x120 > [ 34.707197] softirqs last disabled at (10495): [<ffffffff812ab9f3>] > __irq_exit_rcu+0xc3/0x120 > [ 34.708015] ---[ end trace 0000000000000000 ]--- > [ 34.752127] calling dax_init+0x0/0xff0 [device_dax] @ 1089 > [ 34.754006] initcall dax_init+0x0/0xff0 [device_dax] returned 0 after 422 > usecs > [ 34.759609] calling dax_kmem_init+0x0/0xff0 [kmem] @ 1089 > [ 37.338377] initcall dax_kmem_init+0x0/0xff0 [kmem] returned 0 after > 2577658 usecs > > > > > > Signed-off-by: Dan Williams <[email protected]> > > Signed-off-by: Smita Koralahalli <[email protected]> > > Reviewed-by: Dave Jiang <[email protected]> > > Reviewed-by: Jonathan Cameron <[email protected]> > > --- > > drivers/dax/Makefile | 3 +-- > > drivers/dax/cxl.c | 27 ++++++++++++++++++++++++++- > > 2 files changed, 27 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/dax/Makefile b/drivers/dax/Makefile > > index 5ed5c39857c8..70e996bf1526 100644 > > --- a/drivers/dax/Makefile > > +++ b/drivers/dax/Makefile > > @@ -1,4 +1,5 @@ > > # SPDX-License-Identifier: GPL-2.0 > > +obj-y += hmem/ > > obj-$(CONFIG_DAX) += dax.o > > obj-$(CONFIG_DEV_DAX) += device_dax.o > > obj-$(CONFIG_DEV_DAX_KMEM) += kmem.o > > @@ -10,5 +11,3 @@ dax-y += bus.o > > device_dax-y := device.o > > dax_pmem-y := pmem.o > > dax_cxl-y := cxl.o > > - > > -obj-y += hmem/ > > diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c > > index 13cd94d32ff7..a2136adfa186 100644 > > --- a/drivers/dax/cxl.c > > +++ b/drivers/dax/cxl.c > > @@ -38,10 +38,35 @@ static struct cxl_driver cxl_dax_region_driver = { > > .id = CXL_DEVICE_DAX_REGION, > > .drv = { > > .suppress_bind_attrs = true, > > + .probe_type = PROBE_PREFER_ASYNCHRONOUS, > > }, > > }; > > > > -module_cxl_driver(cxl_dax_region_driver); > > +static void cxl_dax_region_driver_register(struct work_struct *work) > > +{ > > + cxl_driver_register(&cxl_dax_region_driver); > > +} > > + > > +static DECLARE_WORK(cxl_dax_region_driver_work, > > cxl_dax_region_driver_register); > > + > > +static int __init cxl_dax_region_init(void) > > +{ > > + /* > > + * Need to resolve a race with dax_hmem wanting to drive regions > > + * instead of CXL > > + */ > > + queue_work(system_long_wq, &cxl_dax_region_driver_work); > > + return 0; > > +} > > +module_init(cxl_dax_region_init); > > + > > +static void __exit cxl_dax_region_exit(void) > > +{ > > + flush_work(&cxl_dax_region_driver_work); > > + cxl_driver_unregister(&cxl_dax_region_driver); > > +} > > +module_exit(cxl_dax_region_exit); > > + > > MODULE_ALIAS_CXL(CXL_DEVICE_DAX_REGION); > > MODULE_DESCRIPTION("CXL DAX: direct access to CXL regions"); > > MODULE_LICENSE("GPL"); > > -- > > 2.17.1 > > > > >
