On Thu, Jul 19 2001, Linus Torvalds wrote:
>
> I'm getting ready to do a 2.4.7, but one of the fixes in 2.4.7 is a nasty
> SMP race that was found and made it clear that using an old trick of
> having a semaphore on the stack and doing "down()" on it to wait for some
> event (that would do the "up()") was a really bad idea.
Attached are two patches -- one that should fix DAC960 for this new
completion scheme, and one that corrects the corrected comment in
blkdev.h :-)
--
Jens Axboe
--- linux/drivers/block/DAC960.c~ Fri Jul 20 09:18:43 2001
+++ linux/drivers/block/DAC960.c Fri Jul 20 09:18:44 2001
@@ -40,6 +40,7 @@
#include <linux/spinlock.h>
#include <linux/timer.h>
#include <linux/pci.h>
+#include <linux/completion.h>
#include <asm/io.h>
#include <asm/segment.h>
#include <asm/uaccess.h>
@@ -484,14 +485,14 @@
static void DAC960_ExecuteCommand(DAC960_Command_T *Command)
{
DAC960_Controller_T *Controller = Command->Controller;
- DECLARE_MUTEX_LOCKED(Semaphore);
+ DECLARE_COMPLETION(Wait);
unsigned long ProcessorFlags;
- Command->Semaphore = &Semaphore;
+ Command->Waiting = &Wait;
DAC960_AcquireControllerLock(Controller, &ProcessorFlags);
DAC960_QueueCommand(Command);
DAC960_ReleaseControllerLock(Controller, &ProcessorFlags);
if (in_interrupt()) return;
- down(&Semaphore);
+ wait_for_completion(&Wait);
}
@@ -1316,7 +1317,7 @@
*Controller)
{
DAC960_V1_DCDB_T DCDBs[DAC960_V1_MaxChannels], *DCDB;
- Semaphore_T Semaphores[DAC960_V1_MaxChannels], *Semaphore;
+ Completion_T Wait[DAC960_V1_MaxChannels], *wait;
unsigned long ProcessorFlags;
int Channel, TargetID;
for (TargetID = 0; TargetID < Controller->Targets; TargetID++)
@@ -1327,12 +1328,12 @@
DAC960_SCSI_Inquiry_T *InquiryStandardData =
&Controller->V1.InquiryStandardData[Channel][TargetID];
InquiryStandardData->PeripheralDeviceType = 0x1F;
- Semaphore = &Semaphores[Channel];
- init_MUTEX_LOCKED(Semaphore);
+ wait = &Wait[Channel];
+ init_completion(wait);
DCDB = &DCDBs[Channel];
DAC960_V1_ClearCommand(Command);
Command->CommandType = DAC960_ImmediateCommand;
- Command->Semaphore = Semaphore;
+ Command->Waiting = wait;
Command->V1.CommandMailbox.Type3.CommandOpcode = DAC960_V1_DCDB;
Command->V1.CommandMailbox.Type3.BusAddress = Virtual_to_Bus32(DCDB);
DCDB->Channel = Channel;
@@ -1363,11 +1364,11 @@
DAC960_SCSI_Inquiry_UnitSerialNumber_T *InquiryUnitSerialNumber =
&Controller->V1.InquiryUnitSerialNumber[Channel][TargetID];
InquiryUnitSerialNumber->PeripheralDeviceType = 0x1F;
- Semaphore = &Semaphores[Channel];
- down(Semaphore);
+ wait = &Wait[Channel];
+ wait_for_completion(wait);
if (Command->V1.CommandStatus != DAC960_V1_NormalCompletion)
continue;
- Command->Semaphore = Semaphore;
+ Command->Waiting = wait;
DCDB = &DCDBs[Channel];
DCDB->TransferLength = sizeof(DAC960_SCSI_Inquiry_UnitSerialNumber_T);
DCDB->BusAddress = Virtual_to_Bus32(InquiryUnitSerialNumber);
@@ -1381,7 +1382,7 @@
DAC960_AcquireControllerLock(Controller, &ProcessorFlags);
DAC960_QueueCommand(Command);
DAC960_ReleaseControllerLock(Controller, &ProcessorFlags);
- down(Semaphore);
+ wait_for_completion(wait);
}
}
return true;
@@ -2768,7 +2769,7 @@
if (Request->cmd == READ)
Command->CommandType = DAC960_ReadCommand;
else Command->CommandType = DAC960_WriteCommand;
- Command->Semaphore = Request->sem;
+ Command->Waiting = Request->waiting;
Command->LogicalDriveNumber = DAC960_LogicalDriveNumber(Request->rq_dev);
Command->BlockNumber =
Request->sector
@@ -2924,10 +2925,10 @@
/*
Wake up requestor for swap file paging requests.
*/
- if (Command->Semaphore != NULL)
+ if (Command->Waiting)
{
- up(Command->Semaphore);
- Command->Semaphore = NULL;
+ complete(Command->Waiting);
+ Command->Waiting = NULL;
}
add_blkdev_randomness(DAC960_MAJOR + Controller->ControllerNumber);
}
@@ -2969,13 +2970,10 @@
DAC960_ProcessCompletedBuffer(BufferHeader, false);
BufferHeader = NextBufferHeader;
}
- /*
- Wake up requestor for swap file paging requests.
- */
- if (Command->Semaphore != NULL)
+ if (Command->Waiting)
{
- up(Command->Semaphore);
- Command->Semaphore = NULL;
+ complete(Command->Waiting);
+ Command->Waiting = NULL;
}
}
}
@@ -3589,8 +3587,8 @@
}
if (CommandType == DAC960_ImmediateCommand)
{
- up(Command->Semaphore);
- Command->Semaphore = NULL;
+ complete(Command->Waiting);
+ Command->Waiting = NULL;
return;
}
if (CommandType == DAC960_QueuedCommand)
@@ -3931,13 +3929,10 @@
DAC960_ProcessCompletedBuffer(BufferHeader, true);
BufferHeader = NextBufferHeader;
}
- /*
- Wake up requestor for swap file paging requests.
- */
- if (Command->Semaphore != NULL)
+ if (Command->Waiting)
{
- up(Command->Semaphore);
- Command->Semaphore = NULL;
+ complete(Command->Waiting);
+ Command->Waiting = NULL;
}
add_blkdev_randomness(DAC960_MAJOR + Controller->ControllerNumber);
}
@@ -3979,13 +3974,10 @@
DAC960_ProcessCompletedBuffer(BufferHeader, false);
BufferHeader = NextBufferHeader;
}
- /*
- Wake up requestor for swap file paging requests.
- */
- if (Command->Semaphore != NULL)
+ if (Command->Waiting)
{
- up(Command->Semaphore);
- Command->Semaphore = NULL;
+ complete(Command->Waiting);
+ Command->Waiting = NULL;
}
}
}
@@ -4539,8 +4531,8 @@
}
if (CommandType == DAC960_ImmediateCommand)
{
- up(Command->Semaphore);
- Command->Semaphore = NULL;
+ complete(Command->Waiting);
+ Command->Waiting = NULL;
return;
}
if (CommandType == DAC960_QueuedCommand)
--- linux/drivers/block/DAC960.h~ Fri Jul 20 09:14:39 2001
+++ linux/drivers/block/DAC960.h Fri Jul 20 09:14:48 2001
@@ -2153,7 +2153,7 @@
typedef struct pt_regs Registers_T;
typedef struct request IO_Request_T;
typedef request_queue_t RequestQueue_T;
-typedef struct semaphore Semaphore_T;
+typedef struct completion Completion_T;
typedef struct super_block SuperBlock_T;
typedef struct timer_list Timer_T;
typedef wait_queue_head_t WaitQueue_T;
@@ -2220,7 +2220,7 @@
DAC960_CommandType_T CommandType;
struct DAC960_Controller *Controller;
struct DAC960_Command *Next;
- Semaphore_T *Semaphore;
+ Completion_T *Waiting;
unsigned int LogicalDriveNumber;
unsigned int BlockNumber;
unsigned int BlockCount;
--- linux/include/linux/blkdev.h~ Fri Jul 20 09:20:02 2001
+++ linux/include/linux/blkdev.h Fri Jul 20 09:20:14 2001
@@ -14,9 +14,7 @@
/*
* Ok, this is an expanded form so that we can use the same
- * request for paging requests when that is implemented. In
- * paging, 'bh' is NULL, and the completion is used to wait
- * for the IO to be ready.
+ * request for paging requests.
*/
struct request {
struct list_head queue;
