New subject: [ACPI] 5a91d41f89: BUG:sleeping_function_called_from_invalid_context_at_kernel/locking/mutex.c

7 May 2020

Recently a performance problem was reported for a process invoking a
non-trival ASL program. The method call in this case ends up
repetitively triggering a call path like:
acpi_ex_store
    acpi_ex_store_object_to_node
    acpi_ex_write_data_to_field
    acpi_ex_insert_into_field
    acpi_ex_write_with_update_rule
    acpi_ex_field_datum_io
    acpi_ex_access_region
    acpi_ev_address_space_dispatch
    acpi_ex_system_memory_space_handler
    acpi_os_map_cleanup.part.14
    _synchronize_rcu_expedited.constprop.89
    schedule
The end result of frequent synchronize_rcu_expedited() invocation is
tiny sub-millisecond spurts of execution where the scheduler freely
migrates this apparently sleepy task. The overhead of frequent scheduler
invocation multiplies the execution time by a factor of 2-3X.
For example, performance improves from 16 minutes to 7 minutes for a
firmware update procedure across 24 devices.
Perhaps the rcu usage was intended to allow for not taking a sleeping
lock in the acpi_os_{read,write}_memory() path which ostensibly could be
called from an APEI NMI error interrupt? Neither rcu_read_lock() nor
ioremap() are interrupt safe, so add a WARN_ONCE() to validate that rcu
was not serving as a mechanism to avoid direct calls to ioremap(). Even
the original implementation had a spin_lock_irqsave(), but that is not
NMI safe.
APEI itself already has some concept of avoiding ioremap() from
interrupt context (see erst_exec_move_data()), if the new warning
triggers it means that APEI either needs more instrumentation like that
to pre-emptively fail, or more infrastructure to arrange for pre-mapping
the resources it needs in NMI context.
Cc: stable@vger.kernel.org
Fixes: 620242ae8c3d ("ACPI: Maintain a list of ACPI memory mapped I/O remappings")
Cc: Len Brown lenb@kernel.org
Cc: Borislav Petkov bp@alien8.de
Cc: Ira Weiny ira.weiny@intel.com
Cc: James Morse james.morse@arm.com
Cc: Erik Kaneda erik.kaneda@intel.com
Cc: Myron Stowe myron.stowe@redhat.com
Cc: "Rafael J. Wysocki" rjw@rjwysocki.net
Cc: Andy Shevchenko andriy.shevchenko@linux.intel.com
Signed-off-by: Dan Williams dan.j.williams@intel.com
---
Changes since v1 [1]:
- Actually cc: the most important list for ACPI changes (Rafael)
- Cleanup unnecessary variable initialization (Andy)
Link: https://lore.kernel.org/linux-nvdimm/158880834905.2183490.156163294694202340...
drivers/acpi/osl.c |  117 +++++++++++++++++++++++++---------------------------
 1 file changed, 57 insertions(+), 60 deletions(-)

diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index 762c5d50b8fe..a44b75aac5d0 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -214,13 +214,13 @@ acpi_physical_address __init acpi_os_get_root_pointer(void)
    return pa;
 }
-/* Must be called with 'acpi_ioremap_lock' or RCU read lock held. */
 static struct acpi_ioremap *
 acpi_map_lookup(acpi_physical_address phys, acpi_size size)
 {
    struct acpi_ioremap *map;
-	list_for_each_entry_rcu(map, &acpi_ioremaps, list, acpi_ioremap_lock_held())
+	lockdep_assert_held(&acpi_ioremap_lock);
+	list_for_each_entry(map, &acpi_ioremaps, list)
    	if (map->phys <= phys &&
    	    phys + size <= map->phys + map->size)
    		return map;
@@ -228,7 +228,6 @@ acpi_map_lookup(acpi_physical_address phys, acpi_size size)
    return NULL;
 }
-/* Must be called with 'acpi_ioremap_lock' or RCU read lock held. */
 static void __iomem *
 acpi_map_vaddr_lookup(acpi_physical_address phys, unsigned int size)
 {
@@ -263,7 +262,8 @@ acpi_map_lookup_virt(void __iomem *virt, acpi_size size)
 {
    struct acpi_ioremap *map;
-	list_for_each_entry_rcu(map, &acpi_ioremaps, list, acpi_ioremap_lock_held())
+	lockdep_assert_held(&acpi_ioremap_lock);
+	list_for_each_entry(map, &acpi_ioremaps, list)
    	if (map->virt <= virt &&
    	    virt + size <= map->virt + map->size)
    		return map;
@@ -360,7 +360,7 @@ void __iomem __ref
    map->size = pg_sz;
    map->refcount = 1;
-	list_add_tail_rcu(&map->list, &acpi_ioremaps);
+	list_add_tail(&map->list, &acpi_ioremaps);
out:
    mutex_unlock(&acpi_ioremap_lock);
@@ -374,20 +374,13 @@ void *__ref acpi_os_map_memory(acpi_physical_address phys, acpi_size size)
 }
 EXPORT_SYMBOL_GPL(acpi_os_map_memory);
-/* Must be called with mutex_lock(&acpi_ioremap_lock) */
-static unsigned long acpi_os_drop_map_ref(struct acpi_ioremap *map)
-{
-	unsigned long refcount = --map->refcount;
-
-	if (!refcount)
-		list_del_rcu(&map->list);
-	return refcount;
-}
-
-static void acpi_os_map_cleanup(struct acpi_ioremap *map)
+static void acpi_os_drop_map_ref(struct acpi_ioremap *map)
 {
-	synchronize_rcu_expedited();
+	lockdep_assert_held(&acpi_ioremap_lock);
+	if (--map->refcount > 0)
+		return;
    acpi_unmap(map->phys, map->virt);
+	list_del(&map->list);
    kfree(map);
 }
@@ -408,7 +401,6 @@ static void acpi_os_map_cleanup(struct acpi_ioremap *map)
 void __ref acpi_os_unmap_iomem(void __iomem *virt, acpi_size size)
 {
    struct acpi_ioremap *map;
-	unsigned long refcount;
if (!acpi_permanent_mmap) {
    	__acpi_unmap_table(virt, size);
@@ -422,11 +414,8 @@ void __ref acpi_os_unmap_iomem(void __iomem *virt, acpi_size size)
    	WARN(true, PREFIX "%s: bad address %p\n", __func__, virt);
    	return;
    }
-	refcount = acpi_os_drop_map_ref(map);
+	acpi_os_drop_map_ref(map);
    mutex_unlock(&acpi_ioremap_lock);
-
-	if (!refcount)
-		acpi_os_map_cleanup(map);
 }
 EXPORT_SYMBOL_GPL(acpi_os_unmap_iomem);
@@ -461,7 +450,6 @@ void acpi_os_unmap_generic_address(struct acpi_generic_address *gas)
 {
    u64 addr;
    struct acpi_ioremap *map;
-	unsigned long refcount;
if (gas->space_id != ACPI_ADR_SPACE_SYSTEM_MEMORY)
    	return;
@@ -477,11 +465,8 @@ void acpi_os_unmap_generic_address(struct acpi_generic_address *gas)
    	mutex_unlock(&acpi_ioremap_lock);
    	return;
    }
-	refcount = acpi_os_drop_map_ref(map);
+	acpi_os_drop_map_ref(map);
    mutex_unlock(&acpi_ioremap_lock);
-
-	if (!refcount)
-		acpi_os_map_cleanup(map);
 }
 EXPORT_SYMBOL(acpi_os_unmap_generic_address);
@@ -700,55 +685,71 @@ int acpi_os_read_iomem(void __iomem *virt_addr, u64 *value, u32 width)
    return 0;
 }
+static void __iomem *acpi_os_rw_map(acpi_physical_address phys_addr,
+				    unsigned int size, bool *did_fallback)
+{
+	void __iomem *virt_addr;
+
+	if (WARN_ONCE(in_interrupt(), "ioremap in interrupt context\n"))
+		return NULL;
+
+	/* Try to use a cached mapping and fallback otherwise */
+	*did_fallback = false;
+	mutex_lock(&acpi_ioremap_lock);
+	virt_addr = acpi_map_vaddr_lookup(phys_addr, size);
+	if (virt_addr)
+		return virt_addr;
+	mutex_unlock(&acpi_ioremap_lock);
+
+	virt_addr = acpi_os_ioremap(phys_addr, size);
+	*did_fallback = true;
+
+	return virt_addr;
+}
+
+static void acpi_os_rw_unmap(void __iomem *virt_addr, bool did_fallback)
+{
+	if (did_fallback) {
+		/* in the fallback case no lock is held */
+		iounmap(virt_addr);
+		return;
+	}
+
+	mutex_unlock(&acpi_ioremap_lock);
+}
+
 acpi_status
 acpi_os_read_memory(acpi_physical_address phys_addr, u64 *value, u32 width)
 {
-	void __iomem *virt_addr;
    unsigned int size = width / 8;
-	bool unmap = false;
+	bool did_fallback = false;
+	void __iomem *virt_addr;
    u64 dummy;
    int error;
-	rcu_read_lock();
-	virt_addr = acpi_map_vaddr_lookup(phys_addr, size);
-	if (!virt_addr) {
-		rcu_read_unlock();
-		virt_addr = acpi_os_ioremap(phys_addr, size);
-		if (!virt_addr)
-			return AE_BAD_ADDRESS;
-		unmap = true;
-	}
-
+	virt_addr = acpi_os_rw_map(phys_addr, size, &did_fallback);
+	if (!virt_addr)
+		return AE_BAD_ADDRESS;
    if (!value)
    	value = &dummy;
error = acpi_os_read_iomem(virt_addr, value, width);
    BUG_ON(error);
-	if (unmap)
-		iounmap(virt_addr);
-	else
-		rcu_read_unlock();
-
+	acpi_os_rw_unmap(virt_addr, did_fallback);
    return AE_OK;
 }
acpi_status
 acpi_os_write_memory(acpi_physical_address phys_addr, u64 value, u32 width)
 {
-	void __iomem *virt_addr;
    unsigned int size = width / 8;
-	bool unmap = false;
+	bool did_fallback = false;
+	void __iomem *virt_addr;
-	rcu_read_lock();
-	virt_addr = acpi_map_vaddr_lookup(phys_addr, size);
-	if (!virt_addr) {
-		rcu_read_unlock();
-		virt_addr = acpi_os_ioremap(phys_addr, size);
-		if (!virt_addr)
-			return AE_BAD_ADDRESS;
-		unmap = true;
-	}
+	virt_addr = acpi_os_rw_map(phys_addr, size, &did_fallback);
+	if (!virt_addr)
+		return AE_BAD_ADDRESS;
switch (width) {
    case 8:
@@ -767,11 +768,7 @@ acpi_os_write_memory(acpi_physical_address phys_addr, u64 value, u32 width)
    	BUG();
    }
-	if (unmap)
-		iounmap(virt_addr);
-	else
-		rcu_read_unlock();
-
+	acpi_os_rw_unmap(virt_addr, did_fallback);
    return AE_OK;
 }

    

[PATCH v2] ACPI: Drop rcu usage for MMIO mappings