[PATCH] ACPI: NFIT: Fix ARS zero-sized allocation

[Dan Williams]

Pending commit in -next "devres: handle zero size in devm_kmalloc()"
triggers a boot regression due to the ARS implementation expecting NULL
from a zero-sized allocation. Avoid the zero-sized allocation by
skipping ARS, otherwise crashes with the following signature when
de-referencing ZERO_SIZE_PTR.

     BUG: kernel NULL pointer dereference, address: 0000000000000018
     #PF: supervisor read access in kernel mode
     #PF: error_code(0x0000) - not-present page
     RIP: 0010:__acpi_nfit_scrub+0x28a/0x350 [nfit]
     [..]
     Call Trace:
       ? acpi_nfit_query_poison+0x6a/0x180 [nfit]
       acpi_nfit_scrub+0x36/0xb0 [nfit]
       process_one_work+0x23c/0x580
       worker_thread+0x50/0x3b0

Otherwise the implementation correctly aborts when NULL is returned from
devm_kzalloc() in ars_status_alloc().

Cc: Vishal Verma <vishal.l.ve...@intel.com>
Cc: Dave Jiang <dave.ji...@intel.com>
Cc: Ira Weiny <ira.we...@intel.com>
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
---
 drivers/acpi/nfit/core.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
index fb775b967c52..26dd208a0d63 100644
--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -3334,7 +3334,7 @@ static void acpi_nfit_init_ars(struct acpi_nfit_desc 
*acpi_desc,
 static int acpi_nfit_register_regions(struct acpi_nfit_desc *acpi_desc)
 {
        struct nfit_spa *nfit_spa;
-       int rc;
+       int rc, do_sched_ars = 0;
 
        set_bit(ARS_VALID, &acpi_desc->scrub_flags);
        list_for_each_entry(nfit_spa, &acpi_desc->spas, list) {
@@ -3346,7 +3346,7 @@ static int acpi_nfit_register_regions(struct 
acpi_nfit_desc *acpi_desc)
                }
        }
 
-       list_for_each_entry(nfit_spa, &acpi_desc->spas, list)
+       list_for_each_entry(nfit_spa, &acpi_desc->spas, list) {
                switch (nfit_spa_type(nfit_spa->spa)) {
                case NFIT_SPA_VOLATILE:
                case NFIT_SPA_PM:
@@ -3354,6 +3354,13 @@ static int acpi_nfit_register_regions(struct 
acpi_nfit_desc *acpi_desc)
                        rc = ars_register(acpi_desc, nfit_spa);
                        if (rc)
                                return rc;
+
+                       /*
+                        * Kick off background ARS if at least one
+                        * region successfully registered ARS
+                        */
+                       if (!test_bit(ARS_FAILED, &nfit_spa->ars_state))
+                               do_sched_ars++;
                        break;
                case NFIT_SPA_BDW:
                        /* nothing to register */
@@ -3372,8 +3379,10 @@ static int acpi_nfit_register_regions(struct 
acpi_nfit_desc *acpi_desc)
                        /* don't register unknown regions */
                        break;
                }
+       }
 
-       sched_ars(acpi_desc);
+       if (do_sched_ars)
+               sched_ars(acpi_desc);
        return 0;
 }