[Xen-changelog] [xen-unstable] [BLKTAP] Fix SMP debugging assert failures in blktap

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Andrew Warfield <andy@xxxxxxxxxxxxx>
# Node ID 5f5e3b4c6fba7c56df9bc7c29236ba2ae9a9d2a1
# Parent  460f2c954cca7b28e2db89b72cc6594947e08f50
[BLKTAP] Fix SMP debugging assert failures in blktap
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>
---
 linux-2.6-xen-sparse/drivers/xen/blktap/blktap.c |   37 -----------------------
 1 files changed, 1 insertion(+), 36 deletions(-)

diff -r 460f2c954cca -r 5f5e3b4c6fba 
linux-2.6-xen-sparse/drivers/xen/blktap/blktap.c
--- a/linux-2.6-xen-sparse/drivers/xen/blktap/blktap.c  Thu Sep 28 11:52:17 
2006 -0700
+++ b/linux-2.6-xen-sparse/drivers/xen/blktap/blktap.c  Thu Sep 28 12:03:01 
2006 -0700
@@ -694,10 +694,7 @@ static int req_increase(void)
 {
        int i, j;
        struct page *page;
-       unsigned long flags;
        int ret;
-
-       spin_lock_irqsave(&pending_free_lock, flags);
 
        ret = -EINVAL;
        if (mmap_alloc >= MAX_PENDING_REQS || mmap_lock) 
@@ -763,8 +760,7 @@ 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;
 }
 
@@ -792,37 +788,6 @@ 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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