WorkStruct: Pass the work_struct pointer instead of context data

Pass the work_struct pointer to the work function rather than context data.
The work function can use container_of() to work out the data.

For the cases where the container of the work_struct may go away the moment the
pending bit is cleared, it is made possible to defer the release of the
structure by deferring the clearing of the pending bit.

To make this work, an extra flag is introduced into the management side of the
work_struct.  This governs auto-release of the structure upon execution.

Ordinarily, the work queue executor would release the work_struct for further
scheduling or deallocation by clearing the pending bit prior to jumping to the
work function.  This means that, unless the driver makes some guarantee itself
that the work_struct won't go away, the work function may not access anything
else in the work_struct or its container lest they be deallocated..  This is a
problem if the auxiliary data is taken away (as done by the last patch).

However, if the pending bit is *not* cleared before jumping to the work
function, then the work function *may* access the work_struct and its container
with no problems.  But then the work function must itself release the
work_struct by calling work_release().

In most cases, automatic release is fine, so this is the default.  Special
initiators exist for the non-auto-release case (ending in _NAR).


Signed-Off-By: David Howells <dhowells@redhat.com>

1 files changed, 8 insertions, 17 deletions

diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index 068fe4f100b0..02b30ae6a68e 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -50,6 +50,7 @@ ACPI_MODULE_NAME("osl")
 struct acpi_os_dpc {
         acpi_osd_exec_callback function;
         void *context;
+        struct work_struct work;
 };
 
 #ifdef CONFIG_ACPI_CUSTOM_DSDT
@@ -564,12 +565,9 @@ void acpi_os_derive_pci_id(acpi_handle rhandle,	/* upper bound  */
         acpi_os_derive_pci_id_2(rhandle, chandle, id, &is_bridge, &bus_number);
 }
 
-static void acpi_os_execute_deferred(void *context)
+static void acpi_os_execute_deferred(struct work_struct *work)
 {
-        struct acpi_os_dpc *dpc = NULL;
-
-
-        dpc = (struct acpi_os_dpc *)context;
+        struct acpi_os_dpc *dpc = container_of(work, struct acpi_os_dpc, work);
         if (!dpc) {
                 printk(KERN_ERR PREFIX "Invalid (NULL) context\n");
                 return;
@@ -602,7 +600,6 @@ acpi_status acpi_os_execute(acpi_execute_type type,
 {
         acpi_status status = AE_OK;
         struct acpi_os_dpc *dpc;
-        struct work_struct *task;
 
         ACPI_FUNCTION_TRACE("os_queue_for_execution");
 
@@ -615,28 +612,22 @@ acpi_status acpi_os_execute(acpi_execute_type type,
 
         /*
          * Allocate/initialize DPC structure.  Note that this memory will be
-         * freed by the callee.  The kernel handles the tq_struct list  in a
+         * freed by the callee.  The kernel handles the work_struct list  in a
          * way that allows us to also free its memory inside the callee.
          * Because we may want to schedule several tasks with different
          * parameters we can't use the approach some kernel code uses of
-         * having a static tq_struct.
-         * We can save time and code by allocating the DPC and tq_structs
-         * from the same memory.
+         * having a static work_struct.
          */
 
-        dpc =
-            kmalloc(sizeof(struct acpi_os_dpc) + sizeof(struct work_struct),
-                    GFP_ATOMIC);
+        dpc = kmalloc(sizeof(struct acpi_os_dpc), GFP_ATOMIC);
         if (!dpc)
                 return_ACPI_STATUS(AE_NO_MEMORY);
 
         dpc->function = function;
         dpc->context = context;
 
-        task = (void *)(dpc + 1);
-        INIT_WORK(task, acpi_os_execute_deferred, (void *)dpc);
-
-        if (!queue_work(kacpid_wq, task)) {
+        INIT_WORK(&dpc->work, acpi_os_execute_deferred);
+        if (!queue_work(kacpid_wq, &dpc->work)) {
                 ACPI_DEBUG_PRINT((ACPI_DB_ERROR,
                                   "Call to queue_work() failed.\n"));
                 kfree(dpc);