[Qemu-devel] [PATCH V6 0/6] coroutine: mmap stack memory and stack size

[Qemu-devel] [PATCH V6 0/6] coroutine: mmap stack memory and stack size

[Peter Lieven]

I decided to split this from the rest of the Qemu RSS usage series as
it contains the more or less non contentious patches.

I omitted the MAP_GROWSDOWN flag in mmap as we are not 100% sure which
side effects it has.

I kept the guard page which is now nicely makes the stacks visible in
smaps. The old version of the relevent patch lacked the MAP_FIXED flag
in the second call to mmap.

The last patch which reduces the stack size of coroutines to 64kB
may be omitted if its found to risky.

v5->v6:
 - Patch 1: added info that the guard page is deducted from stack memory to
            commit msg and headers [Stefan]
 - rebased to master

v4->v5:
 - Patch 1: check if _SC_THREAD_STACK_MIN is defined
 - Patch 1: guard against sysconf(_SC_THREAD_STACK_MIN) returning -1 [Eric]

v3->v4:
 - Patch 1: add a static function to adjust the stack size [Richard]
 - Patch 1: round up the stack size to multiple of the pagesize.

v2->v3:
 - Patch 1,6: adjusted commit message to mention the guard page [Markus]

v1->v2:
 - Patch 1: added an architecture dependend guard page [Richard]
 - Patch 1: avoid stacks smaller than _SC_THREAD_STACK_MIN [Richard]
 - Patch 1: use mmap+mprotect instead of mmap+mmap [Richard]
 - Patch 5: u_int32_t -> uint32_t [Richard]
 - Patch 5: only available if stack grows down

Peter Lieven (6):
  oslib-posix: add helpers for stack alloc and free
  coroutine: add a macro for the coroutine stack size
  coroutine-ucontext: use helper for allocating stack memory
  coroutine-sigaltstack: use helper for allocating stack memory
  oslib-posix: add a configure switch to debug stack usage
  coroutine: reduce stack size to 64kB

 configure                    | 19 ++++++++++
 include/qemu/coroutine_int.h |  2 ++
 include/sysemu/os-posix.h    | 27 ++++++++++++++
 util/coroutine-sigaltstack.c |  7 ++--
 util/coroutine-ucontext.c    |  9 +++--
 util/coroutine-win32.c       |  2 +-
 util/oslib-posix.c           | 83 ++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 139 insertions(+), 10 deletions(-)

-- 
1.9.1

[Qemu-devel] [PATCH V6 1/6] oslib-posix: add helpers for stack alloc and free

[Peter Lieven]

the allocated stack will be adjusted to the minimum supported stack size
by the OS and rounded up to be a multiple of the system pagesize.
Additionally an architecture dependent guard page is added to the stack
to catch stack overflows. The memory for the guard page is deductated from
stack memory so that the usable stack size is effectively reduced by the size
of one page. This is equivalent to how the glibc stack allocation routines
behave.

Signed-off-by: Peter Lieven <pl@kamp.de>
---
 include/sysemu/os-posix.h | 27 +++++++++++++++++++++++++++
 util/oslib-posix.c        | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 73 insertions(+)

diff --git a/include/sysemu/os-posix.h b/include/sysemu/os-posix.h
index 9c7dfdf..87e60fe 100644
--- a/include/sysemu/os-posix.h
+++ b/include/sysemu/os-posix.h
@@ -60,4 +60,31 @@ int qemu_utimens(const char *path, const qemu_timespec *times);
 
 bool is_daemonized(void);
 
+/**
+ * qemu_alloc_stack:
+ * @sz: size of required stack in bytes
+ *
+ * Allocate memory that can be used as a stack, for instance for
+ * coroutines. If the memory cannot be allocated, this function
+ * will abort (like g_malloc()). This function also inserts a
+ * guard page to catch a potential stack overflow. The memory
+ * for the guard page is deductated from stack memory so that
+ * the usable stack size is effectively sz bytes minus the size
+ * of one page.
+ *
+ * The allocated stack must be freed with qemu_free_stack().
+ *
+ * Returns: pointer to (the lowest address of) the stack memory.
+ */
+void *qemu_alloc_stack(size_t sz);
+
+/**
+ * qemu_free_stack:
+ * @stack: stack to free
+ * @sz: size of stack in bytes
+ *
+ * Free a stack allocated via qemu_alloc_stack().
+ */
+void qemu_free_stack(void *stack, size_t sz);
+
 #endif
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index f2d4e9e..76b028e 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -499,3 +499,49 @@ pid_t qemu_fork(Error **errp)
     }
     return pid;
 }
+
+static size_t adjust_stack_size(size_t sz)
+{
+#ifdef _SC_THREAD_STACK_MIN
+    /* avoid stacks smaller than _SC_THREAD_STACK_MIN */
+    sz = MAX(MAX(sysconf(_SC_THREAD_STACK_MIN), 0), sz);
+#endif
+    /* adjust stack size to a multiple of the page size */
+    sz = ROUND_UP(sz, getpagesize());
+    return sz;
+}
+
+void *qemu_alloc_stack(size_t sz)
+{
+    void *ptr, *guardpage;
+    size_t pagesz = getpagesize();
+    sz = adjust_stack_size(sz);
+
+    ptr = mmap(NULL, sz, PROT_READ | PROT_WRITE,
+               MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    if (ptr == MAP_FAILED) {
+        abort();
+    }
+
+#if defined(HOST_IA64)
+    /* separate register stack */
+    guardpage = ptr + (((sz - pagesz) / 2) & ~pagesz);
+#elif defined(HOST_HPPA)
+    /* stack grows up */
+    guardpage = ptr + sz - pagesz;
+#else
+    /* stack grows down */
+    guardpage = ptr;
+#endif
+    if (mprotect(guardpage, pagesz, PROT_NONE) != 0) {
+        abort();
+    }
+
+    return ptr;
+}
+
+void qemu_free_stack(void *stack, size_t sz)
+{
+    sz = adjust_stack_size(sz);
+    munmap(stack, sz);
+}
-- 
1.9.1

[Qemu-devel] [PATCH V6 2/6] coroutine: add a macro for the coroutine stack size

[Peter Lieven]

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>
---
 include/qemu/coroutine_int.h | 2 ++
 util/coroutine-sigaltstack.c | 2 +-
 util/coroutine-ucontext.c    | 2 +-
 util/coroutine-win32.c       | 2 +-
 4 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/qemu/coroutine_int.h b/include/qemu/coroutine_int.h
index 581a7f5..f62f83f 100644
--- a/include/qemu/coroutine_int.h
+++ b/include/qemu/coroutine_int.h
@@ -28,6 +28,8 @@
 #include "qemu/queue.h"
 #include "qemu/coroutine.h"
 
+#define COROUTINE_STACK_SIZE (1 << 20)
+
 typedef enum {
     COROUTINE_YIELD = 1,
     COROUTINE_TERMINATE = 2,
diff --git a/util/coroutine-sigaltstack.c b/util/coroutine-sigaltstack.c
index a7c3366..9c2854c 100644
--- a/util/coroutine-sigaltstack.c
+++ b/util/coroutine-sigaltstack.c
@@ -143,7 +143,7 @@ static void coroutine_trampoline(int signal)
 
 Coroutine *qemu_coroutine_new(void)
 {
-    const size_t stack_size = 1 << 20;
+    const size_t stack_size = COROUTINE_STACK_SIZE;
     CoroutineUContext *co;
     CoroutineThreadState *coTS;
     struct sigaction sa;
diff --git a/util/coroutine-ucontext.c b/util/coroutine-ucontext.c
index 2bb7e10..31254ab 100644
--- a/util/coroutine-ucontext.c
+++ b/util/coroutine-ucontext.c
@@ -82,7 +82,7 @@ static void coroutine_trampoline(int i0, int i1)
 
 Coroutine *qemu_coroutine_new(void)
 {
-    const size_t stack_size = 1 << 20;
+    const size_t stack_size = COROUTINE_STACK_SIZE;
     CoroutineUContext *co;
     ucontext_t old_uc, uc;
     sigjmp_buf old_env;
diff --git a/util/coroutine-win32.c b/util/coroutine-win32.c
index 02e28e8..de6bd4f 100644
--- a/util/coroutine-win32.c
+++ b/util/coroutine-win32.c
@@ -71,7 +71,7 @@ static void CALLBACK coroutine_trampoline(void *co_)
 
 Coroutine *qemu_coroutine_new(void)
 {
-    const size_t stack_size = 1 << 20;
+    const size_t stack_size = COROUTINE_STACK_SIZE;
     CoroutineWin32 *co;
 
     co = g_malloc0(sizeof(*co));
-- 
1.9.1

[Qemu-devel] [PATCH V6 3/6] coroutine-ucontext: use helper for allocating stack memory

[Peter Lieven]

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>
---
 util/coroutine-ucontext.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/util/coroutine-ucontext.c b/util/coroutine-ucontext.c
index 31254ab..b7dea8c 100644
--- a/util/coroutine-ucontext.c
+++ b/util/coroutine-ucontext.c
@@ -82,7 +82,6 @@ static void coroutine_trampoline(int i0, int i1)
 
 Coroutine *qemu_coroutine_new(void)
 {
-    const size_t stack_size = COROUTINE_STACK_SIZE;
     CoroutineUContext *co;
     ucontext_t old_uc, uc;
     sigjmp_buf old_env;
@@ -101,17 +100,17 @@ Coroutine *qemu_coroutine_new(void)
     }
 
     co = g_malloc0(sizeof(*co));
-    co->stack = g_malloc(stack_size);
+    co->stack = qemu_alloc_stack(COROUTINE_STACK_SIZE);
     co->base.entry_arg = &old_env; /* stash away our jmp_buf */
 
     uc.uc_link = &old_uc;
     uc.uc_stack.ss_sp = co->stack;
-    uc.uc_stack.ss_size = stack_size;
+    uc.uc_stack.ss_size = COROUTINE_STACK_SIZE;
     uc.uc_stack.ss_flags = 0;
 
 #ifdef CONFIG_VALGRIND_H
     co->valgrind_stack_id =
-        VALGRIND_STACK_REGISTER(co->stack, co->stack + stack_size);
+        VALGRIND_STACK_REGISTER(co->stack, co->stack + COROUTINE_STACK_SIZE);
 #endif
 
     arg.p = co;
@@ -149,7 +148,7 @@ void qemu_coroutine_delete(Coroutine *co_)
     valgrind_stack_deregister(co);
 #endif
 
-    g_free(co->stack);
+    qemu_free_stack(co->stack, COROUTINE_STACK_SIZE);
     g_free(co);
 }
 
-- 
1.9.1

[Qemu-devel] [PATCH V6 4/6] coroutine-sigaltstack: use helper for allocating stack memory

[Peter Lieven]

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>
---
 util/coroutine-sigaltstack.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/util/coroutine-sigaltstack.c b/util/coroutine-sigaltstack.c
index 9c2854c..ccf4861 100644
--- a/util/coroutine-sigaltstack.c
+++ b/util/coroutine-sigaltstack.c
@@ -143,7 +143,6 @@ static void coroutine_trampoline(int signal)
 
 Coroutine *qemu_coroutine_new(void)
 {
-    const size_t stack_size = COROUTINE_STACK_SIZE;
     CoroutineUContext *co;
     CoroutineThreadState *coTS;
     struct sigaction sa;
@@ -164,7 +163,7 @@ Coroutine *qemu_coroutine_new(void)
      */
 
     co = g_malloc0(sizeof(*co));
-    co->stack = g_malloc(stack_size);
+    co->stack = qemu_alloc_stack(COROUTINE_STACK_SIZE);
     co->base.entry_arg = &old_env; /* stash away our jmp_buf */
 
     coTS = coroutine_get_thread_state();
@@ -189,7 +188,7 @@ Coroutine *qemu_coroutine_new(void)
      * Set the new stack.
      */
     ss.ss_sp = co->stack;
-    ss.ss_size = stack_size;
+    ss.ss_size = COROUTINE_STACK_SIZE;
     ss.ss_flags = 0;
     if (sigaltstack(&ss, &oss) < 0) {
         abort();
@@ -253,7 +252,7 @@ void qemu_coroutine_delete(Coroutine *co_)
 {
     CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
 
-    g_free(co->stack);
+    qemu_free_stack(co->stack, COROUTINE_STACK_SIZE);
     g_free(co);
 }
 
-- 
1.9.1

[Qemu-devel] [PATCH V6 5/6] oslib-posix: add a configure switch to debug stack usage

[Peter Lieven]

this adds a knob to track the maximum stack usage of stacks
created by qemu_alloc_stack.

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
---
 configure          | 19 +++++++++++++++++++
 util/oslib-posix.c | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/configure b/configure
index 4b808f9..7e087c5 100755
--- a/configure
+++ b/configure
@@ -296,6 +296,7 @@ libiscsi=""
 libnfs=""
 coroutine=""
 coroutine_pool=""
+debug_stack_usage="no"
 seccomp=""
 glusterfs=""
 glusterfs_xlator_opt="no"
@@ -1005,6 +1006,8 @@ for opt do
   ;;
   --enable-coroutine-pool) coroutine_pool="yes"
   ;;
+  --enable-debug-stack-usage) debug_stack_usage="yes"
+  ;;
   --disable-docs) docs="no"
   ;;
   --enable-docs) docs="yes"
@@ -4306,6 +4309,17 @@ if test "$coroutine" = "gthread" -a "$coroutine_pool" = "yes"; then
   error_exit "'gthread' coroutine backend does not support pool (use --disable-coroutine-pool)"
 fi
 
+if test "$debug_stack_usage" = "yes"; then
+  if test "$cpu" = "ia64" -o "$cpu" = "hppa"; then
+    error_exit "stack usage debugging is not supported for $cpu"
+  fi
+  if test "$coroutine_pool" = "yes"; then
+    echo "WARN: disabling coroutine pool for stack usage debugging"
+    coroutine_pool=no
+  fi
+fi
+
+
 ##########################################
 # check if we have open_by_handle_at
 
@@ -4892,6 +4906,7 @@ echo "QGA MSI support   $guest_agent_msi"
 echo "seccomp support   $seccomp"
 echo "coroutine backend $coroutine"
 echo "coroutine pool    $coroutine_pool"
+echo "debug stack usage $debug_stack_usage"
 echo "GlusterFS support $glusterfs"
 echo "Archipelago support $archipelago"
 echo "gcov              $gcov_tool"
@@ -5360,6 +5375,10 @@ else
   echo "CONFIG_COROUTINE_POOL=0" >> $config_host_mak
 fi
 
+if test "$debug_stack_usage" = "yes" ; then
+  echo "CONFIG_DEBUG_STACK_USAGE=y" >> $config_host_mak
+fi
+
 if test "$open_by_handle_at" = "yes" ; then
   echo "CONFIG_OPEN_BY_HANDLE=y" >> $config_host_mak
 fi
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 76b028e..8869f6c 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -50,6 +50,10 @@
 
 #include "qemu/mmap-alloc.h"
 
+#ifdef CONFIG_DEBUG_STACK_USAGE
+#include "qemu/error-report.h"
+#endif
+
 int qemu_get_thread_id(void)
 {
 #if defined(__linux__)
@@ -514,6 +518,9 @@ static size_t adjust_stack_size(size_t sz)
 void *qemu_alloc_stack(size_t sz)
 {
     void *ptr, *guardpage;
+#ifdef CONFIG_DEBUG_STACK_USAGE
+    void *ptr2;
+#endif
     size_t pagesz = getpagesize();
     sz = adjust_stack_size(sz);
 
@@ -537,11 +544,41 @@ void *qemu_alloc_stack(size_t sz)
         abort();
     }
 
+#ifdef CONFIG_DEBUG_STACK_USAGE
+    for (ptr2 = ptr + pagesz; ptr2 < ptr + sz; ptr2 += sizeof(uint32_t)) {
+        *(uint32_t *)ptr2 = 0xdeadbeaf;
+    }
+#endif
+
     return ptr;
 }
 
+#ifdef CONFIG_DEBUG_STACK_USAGE
+static __thread unsigned int max_stack_usage;
+#endif
+
 void qemu_free_stack(void *stack, size_t sz)
 {
+#ifdef CONFIG_DEBUG_STACK_USAGE
+    unsigned int usage;
+    void *ptr;
+#endif
     sz = adjust_stack_size(sz);
+
+#ifdef CONFIG_DEBUG_STACK_USAGE
+    for (ptr = stack + getpagesize(); ptr < stack + sz;
+         ptr += sizeof(uint32_t)) {
+        if (*(uint32_t *)ptr != 0xdeadbeaf) {
+            break;
+        }
+    }
+    usage = sz - (uintptr_t) (ptr - stack);
+    if (usage > max_stack_usage) {
+        error_report("thread %d max stack usage increased from %u to %u",
+                     qemu_get_thread_id(), max_stack_usage, usage);
+        max_stack_usage = usage;
+    }
+#endif
+
     munmap(stack, sz);
 }
-- 
1.9.1

[Qemu-devel] [PATCH V6 6/6] coroutine: reduce stack size to 64kB

[Peter Lieven]

evaluation with the recently introduced maximum stack usage monitoring revealed
that the actual used stack size was never above 4kB so allocating 1MB stack
for each coroutine is a lot of wasted memory. So reduce the stack size to
64kB which should still give enough head room. The guard page added
in qemu_alloc_stack will catch a potential stack overflow introduced
by this commit.

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 include/qemu/coroutine_int.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/qemu/coroutine_int.h b/include/qemu/coroutine_int.h
index f62f83f..011910f 100644
--- a/include/qemu/coroutine_int.h
+++ b/include/qemu/coroutine_int.h
@@ -28,7 +28,7 @@
 #include "qemu/queue.h"
 #include "qemu/coroutine.h"
 
-#define COROUTINE_STACK_SIZE (1 << 20)
+#define COROUTINE_STACK_SIZE (1 << 16)
 
 typedef enum {
     COROUTINE_YIELD = 1,
-- 
1.9.1

Re: [Qemu-devel] [PATCH V6 1/6] oslib-posix: add helpers for stack alloc and free

[Richard Henderson]

On 08/22/2016 06:04 AM, Peter Lieven wrote:
> +static size_t adjust_stack_size(size_t sz)
> +{
> +#ifdef _SC_THREAD_STACK_MIN
> +    /* avoid stacks smaller than _SC_THREAD_STACK_MIN */
> +    sz = MAX(MAX(sysconf(_SC_THREAD_STACK_MIN), 0), sz);
> +#endif

You need to place the sysconf result into a local variable.  What you have now 
expands to 4 invocations of the function.

You might also consider passing in the pagesize, since you've already called 
getpagesize in one of the two users of this function.


r~

Re: [Qemu-devel] [PATCH V6 1/6] oslib-posix: add helpers for stack alloc and free

[Peter Lieven]

Am 22.08.2016 um 17:19 schrieb Richard Henderson:
> On 08/22/2016 06:04 AM, Peter Lieven wrote:
>> +static size_t adjust_stack_size(size_t sz)
>> +{
>> +#ifdef _SC_THREAD_STACK_MIN
>> +    /* avoid stacks smaller than _SC_THREAD_STACK_MIN */
>> +    sz = MAX(MAX(sysconf(_SC_THREAD_STACK_MIN), 0), sz);
>> +#endif
>
> You need to place the sysconf result into a local variable.  What you have now expands to 4 invocations of the function.

okay, I thought it would only be 2 calls and its not critical. but I can change that.

>
> You might also consider passing in the pagesize, since you've already called getpagesize in one of the two users of this function.

I can change this as well, but isn't getpagesize just a macro on most systems?
If the call of getpagesize is critical we should cache it somewhere as there are more critical sections that call it repeatly.

Peter