[Xen-devel] [PATCH] linux-2.6.18/scsiback/usbback: move cond_resched() invocations to proper place

["Jan Beulich" <JBeulich@xxxxxxxx>]

The call to cond_resched() must be inside the loop, in order to not
expose the host to guest induced soft lockups (due to a close to
unbounded loop).

Also rate limit printk()-s in those loops as well as in blktap's.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/drivers/xen/blktap/common.h
+++ b/drivers/xen/blktap/common.h
@@ -41,7 +41,9 @@
 #define DPRINTK(_f, _a...) pr_debug("(file=%s, line=%d) " _f, \
                                     __FILE__ , __LINE__ , ## _a )
 
-#define WPRINTK(fmt, args...) printk(KERN_WARNING "blk_tap: " fmt, ##args)
+#define WPRINTK(fmt, args...) \
+       ((void)(printk_ratelimit() && \
+               printk(KERN_WARNING "blktap: " fmt, ##args)))
 
 struct backend_info;
 
--- a/drivers/xen/scsiback/scsiback.c
+++ b/drivers/xen/scsiback/scsiback.c
@@ -603,40 +603,36 @@ static int _scsiback_do_cmd_fn(struct vs
 
                err = prepare_pending_reqs(info, ring_req,
                                                pending_req);
-               if (err == -EINVAL) {
-                       scsiback_do_resp_with_sense(NULL, (DRIVER_ERROR << 24),
-                               0, pending_req);
-                       continue;
-               } else if (err == -ENODEV) {
-                       scsiback_do_resp_with_sense(NULL, (DID_NO_CONNECT << 
16),
-                               0, pending_req);
-                       continue;
-               }
-
-               if (pending_req->act == VSCSIIF_ACT_SCSI_CDB) {
-
+               switch (err ?: pending_req->act) {
+               case VSCSIIF_ACT_SCSI_CDB:
                        /* The Host mode is through as for Emulation. */
                        if (info->feature == VSCSI_TYPE_HOST)
                                scsiback_cmd_exec(pending_req);
                        else
                                scsiback_req_emulation_or_cmdexec(pending_req);
-
-               } else if (pending_req->act == VSCSIIF_ACT_SCSI_RESET) {
+                       break;
+               case VSCSIIF_ACT_SCSI_RESET:
                        scsiback_device_reset_exec(pending_req);
-               } else {
-                       printk(KERN_ERR "scsiback: invalid parameter for 
request\n");
-                       scsiback_do_resp_with_sense(NULL, (DRIVER_ERROR << 24),
-                               0, pending_req);
-                       continue;
+                       break;
+               default:
+                       if(!err && printk_ratelimit())
+                               printk(KERN_ERR "scsiback: invalid request\n");
+                       scsiback_do_resp_with_sense(NULL, DRIVER_ERROR << 24,
+                                                   0, pending_req);
+                       break;
+               case -ENODEV:
+                       scsiback_do_resp_with_sense(NULL, DID_NO_CONNECT << 16,
+                                                   0, pending_req);
+                       break;
                }
+
+               /* Yield point for this unbounded loop. */
+               cond_resched();
        }
 
        if (RING_HAS_UNCONSUMED_REQUESTS(ring))
                more_to_do = 1;
 
-       /* Yield point for this unbounded loop. */
-       cond_resched();
-
        return more_to_do;
 }
 
--- a/drivers/xen/usbback/usbback.c
+++ b/drivers/xen/usbback/usbback.c
@@ -981,7 +981,9 @@ static int usbbk_start_submit_urb(usbif_
 
        while (rc != rp) {
                if (RING_REQUEST_CONS_OVERFLOW(urb_ring, rc)) {
-                       printk(KERN_WARNING "RING_REQUEST_CONS_OVERFLOW\n");
+                       if(printk_ratelimit())
+                               printk(KERN_WARNING "usbback: "
+                                      "RING_REQUEST_CONS_OVERFLOW\n");
                        break;
                }
 
@@ -996,12 +998,12 @@ static int usbbk_start_submit_urb(usbif_
 
                dispatch_request_to_pending_reqs(usbif, req,
                                                        pending_req);
+
+               cond_resched();
        }
 
        RING_FINAL_CHECK_FOR_REQUESTS(&usbif->urb_ring, more_to_do);
 
-       cond_resched();
-
        return more_to_do;
 }

Attachment: xen-backends-cond-resched.patch
Description: Text document

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