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[Xen-devel] Re: [Patch] Fix SMP debugging assert failures in blktap
- To: "Stephen C. Tweedie" <sct@xxxxxxxxxx>
- From: "Andrew Warfield" <andrew.warfield@xxxxxxxxxxxx>
- Date: Thu, 28 Sep 2006 12:04:36 -0700
- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Julian Chesterfield <jac90@xxxxxxxxx>
- Delivery-date: Thu, 28 Sep 2006 12:05:08 -0700
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Applied, thank you.
a.
On 9/28/06, Stephen C. Tweedie <sct@xxxxxxxxxx> wrote:
blktap is calling non-atomic kernel functions with irqs disabled, which
hits various kernel debug traps if those are enabled. The problem is
req_increase(), which takes the pending_free_lock.
This function is currently only ever called from module initialiation,
where it is impossible for it to race against anything else. Its
companion, req_decrease(), is not called at all.
Fix by removing the offending locking from req_increase() and, while
we're at it, remove req_decrease() entirely.
Signed-off-by: Stephen Tweedie <sct@xxxxxxxxxx>
diff -r ed51caee4fe6 -r 94df5bd84195
linux-2.6-xen-sparse/drivers/xen/blktap/blktap.c
--- a/linux-2.6-xen-sparse/drivers/xen/blktap/blktap.c Thu Sep 28 15:38:25
2006 +0100
+++ b/linux-2.6-xen-sparse/drivers/xen/blktap/blktap.c Thu Sep 28 17:09:09
2006 +0100
@@ -716,8 +716,6 @@ static int req_increase(void)
unsigned long flags;
int ret;
- spin_lock_irqsave(&pending_free_lock, flags);
-
ret = -EINVAL;
if (mmap_alloc >= MAX_PENDING_REQS || mmap_lock)
goto done;
@@ -782,8 +780,7 @@ static int req_increase(void)
mmap_alloc++;
DPRINTK("# MMAPs increased to %d\n",mmap_alloc);
- done:
- spin_unlock_irqrestore(&pending_free_lock, flags);
+done:
return ret;
}
@@ -811,36 +808,6 @@ static void mmap_req_del(int mmap)
mmap_lock = 0;
DPRINTK("# MMAPs decreased to %d\n",mmap_alloc);
mmap_alloc--;
-}
-
-/*N.B. Currently unused - will be accessed via sysfs*/
-static void req_decrease(void)
-{
- pending_req_t *req;
- int i;
- unsigned long flags;
-
- spin_lock_irqsave(&pending_free_lock, flags);
-
- DPRINTK("Req decrease called.\n");
- if (mmap_lock || mmap_alloc == 1)
- goto done;
-
- mmap_lock = 1;
- mmap_inuse = MAX_PENDING_REQS;
-
- /*Go through reqs and remove any that aren't in use*/
- for (i = 0; i < MAX_PENDING_REQS ; i++) {
- req = &pending_reqs[mmap_alloc-1][i];
- if (req->inuse == 0) {
- list_del(&req->free_list);
- mmap_inuse--;
- }
- }
- if (mmap_inuse == 0) mmap_req_del(mmap_alloc-1);
- done:
- spin_unlock_irqrestore(&pending_free_lock, flags);
- return;
}
static pending_req_t* alloc_req(void)
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