This avoids a potential issue with a fork after allocation but before
madvise.
Signed-off-by: Ian Campbell <ian.campb...@citrix.com>
---
v7: New, replacing "tools/libs/call: linux: avoid forking between mmap
and madvise".
---
tools/libs/call/linux.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/tools/libs/call/linux.c b/tools/libs/call/linux.c
index 3641e41..651f380 100644
--- a/tools/libs/call/linux.c
+++ b/tools/libs/call/linux.c
@@ -88,7 +88,7 @@ void *osdep_alloc_pages(xencall_handle *xcall, size_t npages)
{
size_t size = npages * PAGE_SIZE;
void *p;
- int rc, saved_errno;
+ int rc, i, saved_errno;
/* Address returned by mmap is page aligned. */
p = mmap(NULL, size, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS|MAP_LOCKED, -1, 0);
@@ -107,6 +107,18 @@ void *osdep_alloc_pages(xencall_handle *xcall, size_t
npages)
goto out;
}
+ /*
+ * Touch each page in turn to force them to be un-CoWed, in case a
+ * fork happened in another thread at an inopportune moment
+ * above. The madvise() will prevent any subsequent fork calls from
+ * causing the same problem.
+ */
+ for ( i = 0; i < npages ; i++ )
+ {
+ char *c = (char *)p + (i*PAGE_SIZE);
+ *c = 0;
+ }
+
return p;
out:
--
2.1.4
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