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Subjectios_in_flight of CONFIG_BLK_STATS (still) negative in 2.4
Hello,

in this posting I would like to analyze and discuss a bug(?), that
causes the number of I/O requests in flight (ios_in_flight) of the
extended block device statistics (CONFIG_BLK_STATS) to become and stay
negative on various kernels of version 2.4. In turn, this leads to
erroneous display of 100% utilization for certain classes of harddisk
devices with 'iostat -x' and probably other statistic tools relying on
the 13th (last but two) field (ios_in_flight) of extended block device
statistics listed in /proc/partitions.

First I encountered the behavior with 2.4.24 but could reproduce it
with 2.4.33-rc3 (which is now the latest 2.4 kernel version 2.4.33).
There have been various postings concerning this problem in recent
years but to the best of my knowledge no ultimate fix has been merged
into the mainstream kernel so far.

Some past posts [1,4] and debug instrumentation of the kernel (details
later) indicate that apparently some types of block device I/O
requests get enqueued without starting accounting. Unfortunately, on
finishing the same requests accounting is ended. Thus, the accounting
functions are unbalanced and the base line of ios_in_flight (and
probably other counters?) becomes negative without ever recovering
back to zero for idle devices.

At least in my case using an IDE disk ios_in_flight is -5 after
booting without even executing hdparm, which in turn permanently
decrements the value even further. That means, it does not just happen
if you use hdparm but also during kernel initialization on usual
bootup as will be shown later on. Also the problem only appears for
the harddisk block device (hda) but not for its partitions (hdaX).

The obvious hacks to cure the symptom [7,8] won't fix the problem and
might even cause corrupted statistics if a mix of "good" and "bad"
requests gets queued together. I could also confirm that the issue
happens on a single processor system and is not necessarily an SMP
issue [5]. A former fix for SCSI [6] is already part of the kernel and
obviously does not fix the problem here. Hence, there is need for a
real fix.

The general questions is, if those "bad" requests should be accounted?
If so, we need to find all missing accounting starts to pair the
increment and decrement functions accordingly [2]. If not, we could
eliminate the accounting end for "bad" requests as in [1] or in [3].

Chad Talbot's fix [3] works for me both during the booting part and
for hdparm execution. Probably it needs some refactoring. However, it
only fixes issues in ide_end_drive_cmd but there might be more
functions enqueueing "bad" requests (see details below).

Rick Lindsley's fix [1] also works for me both during the booting part
and for hdparm execution. I wonder, if those two conditional
executions should be moved to req_new_io and req_finished_io instead
of add_request and end_that_request_last. That way they should catch
really all "bad" requests no matter where they came from.

Please keep me in CC since I'm currently not subscribed.


Now the details:

Usual requests from the file system and buffer cache roughly take the
following code path and correctly start accounting through req_new_io:

ll_rw_block
submit_bh
generic_make_request
__make_request (request_queue_t->make_request_fn())
req_new_io
account_io_start
up_ios
add_request
drive_stat_acct [update dk_drive_rio,dk_drive_rblk only for READ or WRITE]
list_add(&req->queue, insert_here) >>>ENQUEUE<<<

On finishing requests the following dequeues them and ends accounting:

end_that_request_last, __scsi_end_request
req_finished_io
account_io_end
down_ios

Unfortunately, various places (fgrep -c) call end_that_request_last of
which some may be the culprit:

drivers/block/cciss.c:3
drivers/block/cpqarray.c:2
drivers/block/ll_rw_blk.c:3
drivers/block/sx8.c:1
drivers/ide/ide-cd.c:1
drivers/ide/ide-disk.c:1
drivers/ide/ide-floppy.c:1
drivers/ide/ide-io.c:2
drivers/ide/ide-taskfile.c:1
drivers/ide/ide-tape.c:1
drivers/message/i2o/i2o_block.c:1
drivers/s390/block/dasd.c:1
drivers/s390/char/tapeblock.c:1
drivers/scsi/ide-scsi.c:1

In order to track down, which places call end_that_request_last
without having ever called req_new_io, I instrumented the kernel as
shown in the patch attached to the end of this mail [9]. It enables
matching of the start and end of requests by means of an
ID. Additionally, it prints call traces to be converted into symbols
using ksymoops. The instrumentation of ide_start_request in ide-io.c
is of course an educated guess based on the fact that I noticed
ios_in_flight becoming negative on task_no_data_intr calling
end_that_request_last. Since the serial console log with kernel
messages and interleaved symbols decoded with ksymoops are quite
large, I only report on selected findings here. If anybody is
interested in my full debug log or kernel configuration, I'm happy to
provide them.

The issues start during initialization of the IDE subsystem:

Linux version 2.4.33-rc3 (maiersn@nettc) (gcc version 3.2.3 20030502 (Red Hat Linux 3.2.3-47.fc4)) #18 Fri Aug 11 18:50:00 CEST 2006
...
Uniform Multi-Platform E-IDE driver Revision: 7.00beta4-2.4
ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx
ICH4: IDE controller at PCI slot 00:1f.1
PCI: Found IRQ 12 for device 00:1f.1
PCI: Sharing IRQ 12 with 00:1d.2
ICH4: chipset revision 1
ICH4: not 100% native mode: will probe irqs later
ide0: BM-DMA at 0xf000-0xf007, BIOS settings: hda:DMA, hdb:pio
ide1: BM-DMA at 0xf008-0xf00f, BIOS settings: hdc:pio, hdd:pio
hda: HDS722540VLAT20, ATA DISK drive
ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
hda: attached ide-disk driver.
hda: host protected area => 1
req=c158fe7c:00000000 cmd=97 sec=0,0 dev=3,0 spcl=c158ff0c buf=00000000 !drive->special.all=0 ide_start_request:-
Pid: 1, comm: swapper
c158fdb4 c01b7214 c0227f1c 00000001 c158e23e 00000061 00000000 00000000
00000003 00000000 c158ff0c 00000000 00000000 c0238956 c022e1d1 00000000
00000000 c0250918 00000000 00000006 c158fe7c c02d74d0 c02d7420 c02d74d0
Call Trace: [<c01b7214>] [<c01b7449>] [<c01b7bd0>] [<c01b0aef>] [<c011b69f>]
[<c01b0b47>] [<c01bf660>] [<c01b0070>] [<c01bfa1c>] [<c01c0b48>] [<c01b5b35>]
[<c0105000>] [<c01c0eee>] [<c010507b>] [<c0105000>] [<c010736e>] [<c0105070>]
Trace; c01b7214 <ide_start_request+294/2e0>
Trace; c01b7449 <ide_do_request+1b9/310>
Trace; c01b7bd0 <ide_do_drive_cmd+b0/100>
Trace; c01b0aef <ide_diag_taskfile+7f/b0>
Trace; c011b69f <__call_console_drivers+5f/70>
Trace; c01b0b47 <ide_raw_taskfile+27/30>
Trace; c01bf660 <idedisk_read_native_max_address+50/a0>
Trace; c01b0070 <task_no_data_intr+0/a0>
Trace; c01bfa1c <init_idedisk_capacity+29c/2b0>
Trace; c01c0b48 <idedisk_setup+158/380>
Trace; c01b5b35 <ide_register_subdriver+125/150>
Trace; c0105000 <_stext+0/0>
Trace; c01c0eee <idedisk_init+7e/120>
Trace; c010507b <init+b/100>
Trace; c0105000 <_stext+0/0>
Trace; c010736e <arch_kernel_thread+2e/40>
Trace; c0105070 <init+0/100>
req=c158fe7c:00000000 cmd=97 sec=0,0 dev=3,0 spcl=c158ff0c buf=00000000 !drive->special.all=0 ide_start_request:I
Pid: 0, comm: swapper
c0261eb4 c01b7214 c0227f1c 00000000 c026023e 00000061 00000000 00000000
00000003 00000000 c158ff0c 00000000 00000000 c0238956 c0237fe7 00000000
c158ff58 00000046 00000000 00000282 c158fe7c c02d74d0 c02d7420 c02d74d0
Call Trace: [<c01b7214>] [<c01b7449>] [<c01b7a42>] [<c01aff60>] [<c010a655>]
[<c010a804>] [<c0106fb0>] [<c010cd28>] [<c0106fb0>] [<c0106fd3>] [<c0107062>]
[<c0105000>]
Trace; c01b7214 <ide_start_request+294/2e0>
Trace; c01b7449 <ide_do_request+1b9/310>
Trace; c01b7a42 <ide_intr+f2/130>
Trace; c01aff60 <set_geometry_intr+0/c0>
Trace; c010a655 <handle_IRQ_event+45/70>
Trace; c010a804 <do_IRQ+64/a0>
Trace; c0106fb0 <default_idle+0/40>
Trace; c010cd28 <call_do_IRQ+5/d>
Trace; c0106fb0 <default_idle+0/40>
Trace; c0106fd3 <default_idle+23/40>
Trace; c0107062 <cpu_idle+52/70>
Trace; c0105000 <_stext+0/0>
req=c158fe7c:00000000 cmd=97 sec=0,0 dev=3,0 spcl=c158ff0c buf=00000000 !drive->special.all=1 ide_start_request:I
Pid: 0, comm: swapper
c0261eb4 c01b7214 c0227f1c 00000000 c026023e 00000061 00000000 00000000
00000003 00000000 c158ff0c 00000000 00000001 c0238956 c0237fe7 00000000
c158ff58 00000046 00000000 00000282 c158fe7c c02d74d0 c02d7420 c02d74d0
Call Trace: [<c01b7214>] [<c01b7449>] [<c01b7a42>] [<c01b0020>] [<c010a655>]
[<c010a804>] [<c0106fb0>] [<c010cd28>] [<c0106fb0>] [<c0106fd3>] [<c0107062>]
[<c0105000>]
Trace; c01b7214 <ide_start_request+294/2e0>
Trace; c01b7449 <ide_do_request+1b9/310>
Trace; c01b7a42 <ide_intr+f2/130>
Trace; c01b0020 <recal_intr+0/50>
Trace; c010a655 <handle_IRQ_event+45/70>
Trace; c010a804 <do_IRQ+64/a0>
Trace; c0106fb0 <default_idle+0/40>
Trace; c010cd28 <call_do_IRQ+5/d>
Trace; c0106fb0 <default_idle+0/40>
Trace; c0106fd3 <default_idle+23/40>
Trace; c0107062 <cpu_idle+52/70>
Trace; c0105000 <_stext+0/0>
req=c158fe7c:00000000 cmd=97 sec=0,0 dev=3,0 spcl=c158ff0c buf=00000000 ios=4294967295 account_io_end:I
Pid: 0, comm: swapper
c0261ec4 c01a208c c15d4000 c158fe7c c0261edc c15d4000 00000000 c158fe7c
c01a2f6a c158fe7c c0237fe7 00000286 c158fe7c c01b6603 c158fe7c 000003f6
00000000 00000050 c02d7450 c02d7420 c02d74d0 c158ff0c c01b010c c02d74d0
Call Trace: [<c01a208c>] [<c01a2f6a>] [<c01b6603>] [<c01b010c>] [<c01b7a0a>]
[<c01b0070>] [<c010a655>] [<c010a804>] [<c0106fb0>] [<c010cd28>] [<c0106fb0>]
[<c0106fd3>] [<c0107062>] [<c0105000>]
Trace; c01a208c <req_finished_io+5c/60>
Trace; c01a2f6a <end_that_request_last+2a/70>
Trace; c01b6603 <ide_end_drive_cmd+83/2e0>
Trace; c01b010c <task_no_data_intr+9c/a0>
Trace; c01b7a0a <ide_intr+ba/130>
Trace; c01b0070 <task_no_data_intr+0/a0>
Trace; c010a655 <handle_IRQ_event+45/70>
Trace; c010a804 <do_IRQ+64/a0>
Trace; c0106fb0 <default_idle+0/40>
Trace; c010cd28 <call_do_IRQ+5/d>
Trace; c0106fb0 <default_idle+0/40>
Trace; c0106fd3 <default_idle+23/40>
Trace; c0107062 <cpu_idle+52/70>
Trace; c0105000 <_stext+0/0>

That's the debug output for one single request. The final
account_io_end clearly decrements ios_in_flight to -1 == (signed
int)4294967295. To me it looks like if ide_do_drive_cmd enqueues the
request with list_add(&rq->queue, queue_head). That could be one place
where account starting by req_new_io is missing (or req_finished_io
should be eliminated depending on the point of view). Unfortunately I
don't know the block or IDE subsystem, in order to decide if that's
correct. Any thoughts?

The following two requests similarly lead to erroneous decrements. (I
still don't understand, why I get -5 for ios_in_flight although only 3
requests seem to be "bad".)

req=c158fe70:00000000 cmd=97 sec=0,0 dev=3,0 spcl=c158ff08 buf=00000000 !drive->special.all=1 ide_start_request:-
Pid: 1, comm: swapper
c158fda8 c01b7214 c0227f1c 00000001 c158e23e 00000061 00000000 00000000
00000003 00000000 c158ff08 00000000 00000001 c0238956 c022e1d1 00000000
c024d560 c158e000 00000000 00000006 c158fe70 c02d74d0 c02d7420 c02d74d0
Call Trace: [<c01b7214>] [<c01b7449>] [<c01b7bd0>] [<c01b0aef>] [<c01b0b47>]
[<c01bf709>] [<c01b0070>] [<c01bf98c>] [<c01c0b48>] [<c01b5b35>] [<c0105000>]
[<c01c0eee>] [<c010507b>] [<c0105000>] [<c010736e>] [<c0105070>]
Trace; c01b7214 <ide_start_request+294/2e0>
Trace; c01b7449 <ide_do_request+1b9/310>
Trace; c01b7bd0 <ide_do_drive_cmd+b0/100>
Trace; c01b0aef <ide_diag_taskfile+7f/b0>
Trace; c01b0b47 <ide_raw_taskfile+27/30>
Trace; c01bf709 <idedisk_read_native_max_address_ext+59/d0>
Trace; c01b0070 <task_no_data_intr+0/a0>
Trace; c01bf98c <init_idedisk_capacity+20c/2b0>
Trace; c01c0b48 <idedisk_setup+158/380>
Trace; c01b5b35 <ide_register_subdriver+125/150>
Trace; c0105000 <_stext+0/0>
Trace; c01c0eee <idedisk_init+7e/120>
Trace; c010507b <init+b/100>
Trace; c0105000 <_stext+0/0>

hda: 80418240 sectors (41174 MB) w/1794KiB Cache, CHS=5005/255/63, UDMA(100)

req=c158fea4:00000000 cmd=97 sec=0,0 dev=3,0 spcl=c158ff34 buf=00000000 !drive->special.all=0 ide_start_request:-
Pid: 1, comm: swapper
c158fddc c01b7214 c0227f1c 00000001 c158e23e 00000061 00000000 00000000
00000003 00000000 c158ff34 00000000 00000000 c0238956 c022e1d1 00000000
c158e000 00000000 00000000 00000006 c158fea4 c02d74d0 c02d7420 c02d74d0
Call Trace: [<c01b7214>] [<c01b7449>] [<c01b7bd0>] [<c01b0aef>] [<c01b0b47>]
[<c01c00f3>] [<c01b0070>] [<c01bd435>] [<c01c0ce8>] [<c0105000>] [<c01c0eee>]
[<c010507b>] [<c0105000>] [<c010736e>] [<c0105070>]
Trace; c01b7214 <ide_start_request+294/2e0>
Trace; c01b7449 <ide_do_request+1b9/310>
Trace; c01b7bd0 <ide_do_drive_cmd+b0/100>
Trace; c01b0aef <ide_diag_taskfile+7f/b0>
Trace; c01b0b47 <ide_raw_taskfile+27/30>
Trace; c01c00f3 <write_cache+73/a0>
Trace; c01b0070 <task_no_data_intr+0/a0>
Trace; c01bd435 <__ide_dma_verbose+c5/1f0>
Trace; c01c0ce8 <idedisk_setup+2f8/380>
Trace; c0105000 <_stext+0/0>
Trace; c01c0eee <idedisk_init+7e/120>
Trace; c010507b <init+b/100>
Trace; c0105000 <_stext+0/0>
Trace; c010736e <arch_kernel_thread+2e/40>
Trace; c0105070 <init+0/100>

Partition check:
hda:

[[at this point, some "good" requests are processed and accounted correctly]]

hda1 hda2 hda3 hda4 <

[[at this point, some "good" requests are processed and accounted correctly]]

hda5 hda6 hda7 hda8 hda9 >

That's all for now.

Thanks,
Steffen.

--

REFERENCES:

[1]
hint to unbalanced requests
fix to never account non-blk_fs_request's and thus eliminating wrong
req_finished_io
http://www.uwsg.iu.edu/hypermail/linux/kernel/0401.1/1353.html
Rick Lindsley
diff -rup linux-2.4.33-rc3/drivers/block/ll_rw_blk.c linux-2.4.33-rc3.rl/drivers/block/ll_rw_blk.c
--- linux-2.4.33-rc3/drivers/block/ll_rw_blk.c 2006-08-08 18:45:09.000000000 +0200
+++ linux-2.4.33-rc3.rl/drivers/block/ll_rw_blk.c 2006-08-17 16:38:27.000000000 +0200
@@ -854,7 +854,8 @@ EXPORT_SYMBOL(req_finished_io);
static inline void add_request(request_queue_t * q, struct request * req,
struct list_head *insert_here)
{
- drive_stat_acct(req->rq_dev, req->cmd, req->nr_sectors, 1);
+ if (blk_fs_request(req))
+ drive_stat_acct(req->rq_dev, req->cmd, req->nr_sectors, 1);

if (!q->plugged && q->head_active && insert_here == &q->queue_head) {
spin_unlock_irq(&io_request_lock);
@@ -1495,7 +1496,8 @@ void end_that_request_last(struct reques
if (laptop_mode && req->cmd == READ)
mod_timer(&writeback_timer, jiffies + 5 * HZ);

- req_finished_io(req);
+ if (blk_fs_request(req))
+ req_finished_io(req);
blkdev_release_request(req);
if (waiting)
complete(waiting);
[2]
need to pair accounting
http://www.uwsg.iu.edu/hypermail/linux/kernel/0309.3/0036.html
Stephen C. Tweedie

[3]
fix replaces end_that_request_last in ide_end_drive_cmd by the content
of end_that_request_last minus req_finished_io
http://www.uwsg.iu.edu/hypermail/linux/kernel/0309.2/1454.html
Chad Talbott
diff -rup linux-2.4.33-rc3/drivers/ide/ide-io.c linux-2.4.33-rc3.ct/drivers/ide/ide-io.c
--- linux-2.4.33-rc3/drivers/ide/ide-io.c 2006-08-08 18:45:09.000000000 +0200
+++ linux-2.4.33-rc3.ct/drivers/ide/ide-io.c 2006-08-17 18:03:18.000000000 +0200
@@ -116,6 +116,7 @@ void ide_end_drive_cmd (ide_drive_t *dri
ide_hwif_t *hwif = HWIF(drive);
unsigned long flags;
struct request *rq;
+ struct completion *waiting;

spin_lock_irqsave(&io_request_lock, flags);
rq = HWGROUP(drive)->rq;
@@ -189,7 +190,12 @@ void ide_end_drive_cmd (ide_drive_t *dri
spin_lock_irqsave(&io_request_lock, flags);
blkdev_dequeue_request(rq);
HWGROUP(drive)->rq = NULL;
- end_that_request_last(rq);
+ waiting = rq->waiting;
+ /* FIXME: laptop_mode behavior of end_that_request_last is
+ * missing because writeback_timer is static in ll_rw_blk.c */
+ blkdev_release_request(rq);
+ if (waiting)
+ complete(waiting);
spin_unlock_irqrestore(&io_request_lock, flags);
}

[4]
hints where accounting starts could be missing
(but it's not an exclusive hdparm issue, it rather
happens during kernel init, even before init is spawned)
http://www.uwsg.iu.edu/hypermail/linux/kernel/0309.1/2327.html
Chad Talbott
[5]
fix to count atomically on SMP (but does not help here)
http://www.uwsg.iu.edu/hypermail/linux/kernel/0207.3/0721.html
Jochen Suckfuell

[6]
fix for scsi_lib is in the mainstream
(but does not fix the issue here)
http://www.uwsg.iu.edu/hypermail/linux/kernel/0207.1/0323.html
Jochen Suckfuell
acknowledged as bug
http://www.uwsg.iu.edu/hypermail/linux/kernel/0207.1/0843.html
Jens Axboe

[7]
hack to reset ios_in_flight to zero if negative on reading procfs
http://www.uwsg.iu.edu/hypermail/linux/kernel/0204.1/0902.html
Jochen Suckfuell

[8]
hack to prevent decrement past zero
http://www.uwsg.iu.edu/hypermail/linux/kernel/0204.1/0703.html
Zlatko Calusic

[9]
diff -ur linux-2.4.33-rc3/drivers/block/ll_rw_blk.c linux-2.4.33-rc3.blkstatfix/drivers/block/ll_rw_blk.c
--- linux-2.4.33-rc3/drivers/block/ll_rw_blk.c 2006-08-08 18:45:09.000000000 +0200
+++ linux-2.4.33-rc3.blkstatfix/drivers/block/ll_rw_blk.c 2006-08-17 10:45:30.000000000 +0200
@@ -32,6 +32,8 @@
#include <linux/slab.h>
#include <linux/module.h>

+#include <linux/interrupt.h>
+
/*
* MAC Floppy IWM hooks
*/
@@ -761,6 +763,8 @@
hd->last_idle_time = now;
}

+static unsigned int blkstatfix_count = 42;
+
static inline void down_ios(struct hd_struct *hd)
{
disk_round_stats(hd);
@@ -790,6 +794,22 @@
}
if (!merge)
up_ios(hd);
+#if 1
+ if (blkstatfix_count > 0) {
+ /* blkstatfix_count--; */
+ printk(KERN_ERR "\nreq=%p:%08lx cmd=%i sec=%lu,%lu dev=%u,%u spcl=%p buf=%p ios=%010u mrg=%i secs=%i %s:%s\n\n",
+ req, req->start_time, req->cmd,
+ req->sector, req->nr_sectors,
+ MAJOR(req->rq_dev), MINOR(req->rq_dev),
+ req->special, req->buffer,
+ hd->ios_in_flight,
+ merge, sectors,
+ __PRETTY_FUNCTION__, (in_interrupt()?"I":"-")
+ );
+ printk("Pid: %d, comm: %20s\n", current->pid, current->comm);
+ dump_stack(); /* from kernel.h, arch/.../kernel/traps.c */
+ }
+#endif
}

static void account_io_end(struct hd_struct *hd, struct request *req)
@@ -806,6 +826,21 @@
break;
}
down_ios(hd);
+#if 1
+ if (blkstatfix_count > 0) {
+ blkstatfix_count--;
+ printk(KERN_ERR "\nreq=%p:%08lx cmd=%i sec=%lu,%lu dev=%u,%u spcl=%p buf=%p ios=%010u %s:%s\n\n",
+ req, req->start_time, req->cmd,
+ req->sector, req->nr_sectors,
+ MAJOR(req->rq_dev), MINOR(req->rq_dev),
+ req->special, req->buffer,
+ hd->ios_in_flight,
+ __PRETTY_FUNCTION__, (in_interrupt()?"I":"-")
+ );
+ printk("Pid: %d, comm: %20s\n", current->pid, current->comm);
+ dump_stack(); /* from kernel.h, arch/.../kernel/traps.c */
+ }
+#endif
}

void req_new_io(struct request *req, int merge, int sectors)
@@ -828,6 +863,22 @@
down_ios(hd1);
if (hd2)
down_ios(hd2);
+#if 1
+ if (blkstatfix_count > 0) {
+ blkstatfix_count--;
+ printk(KERN_ERR "\nreq=%p:%08lx cmd=%i sec=%lu,%lu dev=%u,%u spcl=%p buf=%p ios1=%010u ios2=%010u %s:%s\n\n",
+ req, req->start_time, req->cmd,
+ req->sector, req->nr_sectors,
+ MAJOR(req->rq_dev), MINOR(req->rq_dev),
+ req->special, req->buffer,
+ (hd1)?hd1->ios_in_flight:666,
+ (hd2)?hd2->ios_in_flight:666,
+ __PRETTY_FUNCTION__, (in_interrupt()?"I":"-")
+ );
+ printk("Pid: %d, comm: %20s\n", current->pid, current->comm);
+ dump_stack(); /* from kernel.h, arch/.../kernel/traps.c */
+ }
+#endif
}

void req_finished_io(struct request *req)
diff -ur linux-2.4.33-rc3/drivers/ide/ide-io.c linux-2.4.33-rc3.blkstatfix/drivers/ide/ide-io.c
--- linux-2.4.33-rc3/drivers/ide/ide-io.c 2006-08-08 18:45:09.000000000 +0200
+++ linux-2.4.33-rc3.blkstatfix/drivers/ide/ide-io.c 2006-08-17 10:45:01.000000000 +0200
@@ -541,6 +541,8 @@

EXPORT_SYMBOL(execute_drive_cmd);

+static unsigned int blkstatfix_count = 42;
+
/**
* ide_start_request - start of I/O and command issuing for IDE
*
@@ -610,6 +612,22 @@
printk(KERN_ERR "%s: drive not ready for command\n", drive->name);
return startstop;
}
+#if 1
+ if ((blkstatfix_count > 0)
+ && (1 || !blk_fs_request(rq))) {
+ blkstatfix_count--;
+ printk(KERN_ERR "\nreq=%p:%08lx cmd=%i sec=%lu,%lu dev=%u,%u spcl=%p buf=%p !drive->special.all=%i %s:%s\n\n",
+ rq, rq->start_time, rq->cmd,
+ rq->sector, rq->nr_sectors,
+ MAJOR(rq->rq_dev), MINOR(rq->rq_dev),
+ rq->special, rq->buffer,
+ !drive->special.all,
+ __PRETTY_FUNCTION__, (in_interrupt()?"I":"-")
+ );
+ printk("Pid: %d, comm: %20s\n", current->pid, current->comm);
+ dump_stack(); /* from kernel.h, arch/.../kernel/traps.c */
+ }
+#endif
if (!drive->special.all) {
switch(rq->cmd) {
case IDE_DRIVE_CMD:
-
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