This patch makes all functions in core/mmu.cc that take vma_list_mutex
for write to pre-fault the stack two pages deep before using the mutex.
This is necessary to prevent any follow up stack faults down the call stack
after the vma_list_mutex is take for write as this would lead to a deadlock
experienced when testing one of the apps when the page fault handler and
mmu::vm_fault() function would try to take the same vma_list_mutex for read.
Signed-off-by: Waldemar Kozaczuk <jwkozac...@gmail.com>
---
core/mmu.cc | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/core/mmu.cc b/core/mmu.cc
index 007d4331..e41de215 100644
--- a/core/mmu.cc
+++ b/core/mmu.cc
@@ -47,6 +47,17 @@ extern const char text_start[], text_end[];
namespace mmu {
+#if CONF_lazy_stack
+// We need to ensure that lazy stack is populated deeply enough (2 pages)
+// for all the cases when the vma_list_mutex is taken for write to prevent
+// page faults triggered on stack. The page-fault handling logic would
+// attempt to take same vma_list_mutex fo read and end up with a deadlock.
+#define PREVENT_STACK_PAGE_FAULT \
+ arch::ensure_next_two_stack_pages();
+#else
+#define PREVENT_STACK_PAGE_FAULT
+#endif
+
struct vma_range_compare {
bool operator()(const vma_range& a, const vma_range& b) {
return a.start() < b.start();
@@ -1271,6 +1282,7 @@ static void nohugepage(void* addr, size_t length)
error advise(void* addr, size_t size, int advice)
{
+ PREVENT_STACK_PAGE_FAULT
WITH_LOCK(vma_list_mutex.for_write()) {
if (!ismapped(addr, size)) {
return make_error(ENOMEM);
@@ -1310,6 +1322,7 @@ void* map_anon(const void* addr, size_t size, unsigned
flags, unsigned perm)
size = align_up(size, mmu::page_size);
auto start = reinterpret_cast<uintptr_t>(addr);
auto* vma = new mmu::anon_vma(addr_range(start, start + size), perm,
flags);
+ PREVENT_STACK_PAGE_FAULT
SCOPE_LOCK(vma_list_mutex.for_write());
auto v = (void*) allocate(vma, start, size, search);
if (flags & mmap_populate) {
@@ -1336,6 +1349,7 @@ void* map_file(const void* addr, size_t size, unsigned
flags, unsigned perm,
auto start = reinterpret_cast<uintptr_t>(addr);
auto *vma = f->mmap(addr_range(start, start + size), flags | mmap_file,
perm, offset).release();
void *v;
+ PREVENT_STACK_PAGE_FAULT
WITH_LOCK(vma_list_mutex.for_write()) {
v = (void*) allocate(vma, start, size, search);
if (flags & mmap_populate) {
@@ -1708,6 +1722,7 @@ ulong map_jvm(unsigned char* jvm_addr, size_t size,
size_t align, balloon_ptr b)
auto* vma = new mmu::jvm_balloon_vma(jvm_addr, start, start + size, b,
v->perm(), v->flags());
+ PREVENT_STACK_PAGE_FAULT
WITH_LOCK(vma_list_mutex.for_write()) {
// This means that the mapping that we had before was a balloon mapping
// that was laying around and wasn't updated to an anon mapping. If we
@@ -2014,6 +2029,7 @@ void free_initial_memory_range(uintptr_t addr, size_t
size)
error mprotect(const void *addr, size_t len, unsigned perm)
{
+ PREVENT_STACK_PAGE_FAULT
SCOPE_LOCK(vma_list_mutex.for_write());
if (!ismapped(addr, len)) {
@@ -2025,6 +2041,7 @@ error mprotect(const void *addr, size_t len, unsigned
perm)
error munmap(const void *addr, size_t length)
{
+ PREVENT_STACK_PAGE_FAULT
SCOPE_LOCK(vma_list_mutex.for_write());
length = align_up(length, mmu::page_size);
--
2.34.1
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