Hello,
I resend this e-mail, as it may not be sent properly.
Please excuse me, if you receive same one.
I found a possible bug by which the first get_request() for a process
fails in cfq I/O scheduler.
If it's a bug, please consider to apply the patch for 2.6.12-rc5 below.
When cfq I/O scheduler is selected, get_request() in __make_request()
calls __cfq_get_queue().
__cfq_get_queue() finds an existing queue (struct cfq_queue) of the
current process for the device and returns it. If it's not found,
__cfq_get_queue() creates and returns a new one if __cfq_get_queue()
is called with __GFP_WAIT flag, or __cfq_get_queue() returns NULL
(this means that get_request() fails) if no __GFP_WAIT flag.
On the other hand, in __make_request(), get_request() is called
without __GFP_WAIT flag at the first time.
Thus, the get_request() fails when there is no existing queue,
typically when it's called for the first I/O request of the process
to the device.
Though it will be followed by get_request_wait() for general case,
__make_request() will just end the I/O with an error (EWOULDBLOCK)
when the request was for read-ahead.
The patch for 2.6.12-rc5 is below:
Signed-off-by: Kiyoshi Ueda <[email protected]>
Signed-off-by: Jun'ichi Nomura <[email protected]>
diff -rup linux-2.6.12-rc5/drivers/block/cfq-iosched.c cfq-fix/drivers/block/cfq-iosched.c
--- linux-2.6.12-rc5/drivers/block/cfq-iosched.c 2005-05-24 23:31:20.000000000 -0400
+++ cfq-fix/drivers/block/cfq-iosched.c 2005-06-06 14:20:49.000000000 -0400
@@ -1202,13 +1202,16 @@ retry:
if (new_cfqq) {
cfqq = new_cfqq;
new_cfqq = NULL;
- } else if (gfp_mask & __GFP_WAIT) {
+ } else {
spin_unlock_irq(cfqd->queue->queue_lock);
new_cfqq = kmem_cache_alloc(cfq_pool, gfp_mask);
spin_lock_irq(cfqd->queue->queue_lock);
+
+ if (!new_cfqq && !(gfp_mask & __GFP_WAIT))
+ goto out;
+
goto retry;
- } else
- goto out;
+ }
memset(cfqq, 0, sizeof(*cfqq));
Best regards,
Kiyoshi Ueda
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