[Xen-changelog] Fix a race condition for multi-thread qemu dma, where vmx linux guests

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

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID 3c687c6905e79747953b0458fa5cd5ec83560e44
# Parent  ec370b3d2df3043989b7cb996c28e458d0b5304f
Fix a race condition for multi-thread qemu dma, where vmx linux guests
show warning "dma interrupt lost" and dma becomes very slow.

root cause: In the time between set ide irq and set dma status, if guest
receive the irq and query the status, it will find the status is not
ready and therefore treat it as pseudo interrupt. Change the order of
set irq and set dma status fixes this issue.

Signed-off-by: Ke Yu <ke.yu@xxxxxxxxx>

diff -r ec370b3d2df3 -r 3c687c6905e7 tools/ioemu/hw/ide.c
--- a/tools/ioemu/hw/ide.c      Tue Nov 29 01:00:10 2005
+++ b/tools/ioemu/hw/ide.c      Tue Nov 29 10:38:53 2005
@@ -669,6 +669,8 @@
     }
     if (s->io_buffer_index >= s->io_buffer_size && s->nsector == 0) {
         s->status = READY_STAT | SEEK_STAT;
+        s->bmdma->status &= ~BM_STATUS_DMAING;
+        s->bmdma->status |= BM_STATUS_INT;
         ide_set_irq(s);
 #ifdef DEBUG_IDE_ATAPI
         printf("dma status=0x%x\n", s->status);
@@ -736,6 +738,8 @@
             if (n == 0) {
                 /* end of transfer */
                 s->status = READY_STAT | SEEK_STAT;
+                s->bmdma->status &= ~BM_STATUS_DMAING;
+                s->bmdma->status |= BM_STATUS_INT;
                 ide_set_irq(s);
                 return 0;
             }
@@ -983,6 +987,8 @@
     if (s->packet_transfer_size <= 0) {
         s->status = READY_STAT;
         s->nsector = (s->nsector & ~7) | ATAPI_INT_REASON_IO | 
ATAPI_INT_REASON_CD;
+        s->bmdma->status &= ~BM_STATUS_DMAING;
+        s->bmdma->status |= BM_STATUS_INT;
         ide_set_irq(s);
 #ifdef DEBUG_IDE_ATAPI
         printf("dma status=0x%x\n", s->status);
@@ -2065,8 +2071,6 @@
     }
     /* end of transfer */
  the_end:
-    bm->status &= ~BM_STATUS_DMAING;
-    bm->status |= BM_STATUS_INT;
     bm->dma_cb = NULL;
     bm->ide_if = NULL;
 }

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