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 <sc...@redhat.com>

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)