unwind-libdw: use the mmap_notify subsystem

The unwind subsystem uses the mmap_cache subsystem even it uses
unwind-libdw as backend. unwind-libdw doesn't need the full set of the
mmap_cache subsystem; libdw has a feature for caching a memory
mapping.

This commit does three things.

(1) Make the unwind subsystem not use the mmap_cache subsystem.
The unwind subsystem never concern the memory mapping of the target.
It becomes a thin layer.

(2) Make unwind-libunwind use the mmap_cache subsystem directly.

(3) Make unwind-libdw use the mmap_notify subsystem to know when it
should call dwfl_linux_proc_report/dwfl_report_end for updating the
cache.

Here is a subsystem structure that this patch
introduces:

	+-------------------------------------+
	|            unwind subsys            |
	+------------------+------------------+
	| unwind-libunwind |   unwind-libdw   |
	+------------------+------------------+
	|    mmap_cache    |                  |
	+------------------+                  |
	|               mmap_notify           |
	+-------------------------------------+
	|                syscall              |
	+-------------------------------------+
               mmap/munmap/mprotect/brk...

* unwind.c: Don't include "mmap_cache.h".
(unwind_init): Don't call mmap_cache_enable.
(unwind_tcb_print, unwind_tcb_capture): Don't call mmap_cache related
functions, just invoke unwinder.tcb_walk.
* unwind.h (struct unwind_unwinder_t): Remove tcb_flush_cache field.

* unwind-libdw.c: Include "mmap_notify.h" instead of "mmap_cache.h".
(struct ctx): Add last_proc_updating field to record the generation
of memory mapping that is cached by dwfl_linux_proc_report
and dwfl_report_end.
(mapping_generation): A variable counting how many times the memory
mapping of targets has been changed.
(updating_mapping_generation): New utility function for updating
mapping_generation.
(init): New function for registering updating_mapping_generation
in the mmap_notify subsystem as a callback function.
(tcb_init): Initialize ctx::last_proc_updating.
(tcb_flush_cache): Rename to flush_cache_maybe.  Rebuild the cache data
only if the data is stale.
(tcb_walk): Call flush_cache_maybe for avoiding referring staled cache data.
(unwinder): Set init function, remove tcb_flush_cache field.
* unwind-libunwind.c (init): Enable the mmap_cache subsystem.
(tcb_walk): Call mmap_cache_rebuild_if_invalid and unw_flush_cache for
updating the cache of the memory mapping before walking the stack.
(tcb_walk): Rename to walk.
(unwinder): Remove tcb_flush_cache field.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>

diff --git a/unwind-libdw.c b/unwind-libdw.c
index b20ba20445ff637f7cafb2e4b8fe909c45309e88..603914650fac0aa6d089015283254d116fa71681 100644 (file)
--- a/unwind-libdw.c
+++ b/unwind-libdw.c
@@ -36,13 +36,28 @@
 
 #include "defs.h"
 #include "unwind.h"
-#include "mmap_cache.h"
+#include "mmap_notify.h"
 #include <elfutils/libdwfl.h>
 
 struct ctx {
        Dwfl *dwfl;
+       unsigned int last_proc_updating;
 };
 
+static unsigned int mapping_generation;
+
+static void
+update_mapping_generation(struct tcb *tcp, void *unused)
+{
+       mapping_generation++;
+}
+
+static void
+init(void)
+{
+       mmap_notify_register_client(update_mapping_generation, NULL);
+}
+
 static void *
 tcb_init(struct tcb *tcp)
 {
@@ -74,6 +89,7 @@ tcb_init(struct tcb *tcp)
 
        struct ctx *ctx = xmalloc(sizeof(*ctx));
        ctx->dwfl = dwfl;
+       ctx->last_proc_updating = 0;
        return ctx;
 }
 
@@ -87,6 +103,31 @@ tcb_fin(struct tcb *tcp)
        }
 }
 
+static void
+flush_cache_maybe(struct tcb *tcp)
+{
+       struct ctx *ctx = tcp->unwind_ctx;
+       if (!ctx)
+               return;
+
+       if (ctx->last_proc_updating == mapping_generation)
+               return;
+
+       int r = dwfl_linux_proc_report(ctx->dwfl, tcp->pid);
+
+       if (r < 0)
+               error_msg("dwfl_linux_proc_report returned an error"
+                         " for pid %d: %s", tcp->pid, dwfl_errmsg(-1));
+       else if (r > 0)
+               error_msg("dwfl_linux_proc_report returned an error"
+                         " for pid %d", tcp->pid);
+       else if (dwfl_report_end(ctx->dwfl, NULL, NULL) != 0)
+               error_msg("dwfl_report_end returned an error"
+                         " for pid %d: %s", tcp->pid, dwfl_errmsg(-1));
+
+       ctx->last_proc_updating = mapping_generation;
+}
+
 struct frame_user_data {
        unwind_call_action_fn call_action;
        unwind_error_action_fn error_action;
@@ -150,6 +191,9 @@ tcb_walk(struct tcb *tcp,
                .data = data,
                .stack_depth = 256,
        };
+
+       flush_cache_maybe(tcp);
+
        int r = dwfl_getthread_frames(ctx->dwfl, tcp->pid, frame_callback,
                                      &user_data);
        if (r)
@@ -158,31 +202,10 @@ tcb_walk(struct tcb *tcp,
                             0);
 }
 
-static void
-tcb_flush_cache(struct tcb *tcp)
-{
-       struct ctx *ctx = tcp->unwind_ctx;
-       if (!ctx)
-               return;
-
-       int r = dwfl_linux_proc_report(ctx->dwfl, tcp->pid);
-
-       if (r < 0)
-               error_msg("dwfl_linux_proc_report returned an error"
-                         " for pid %d: %s", tcp->pid, dwfl_errmsg(-1));
-       else if (r > 0)
-               error_msg("dwfl_linux_proc_report returned an error"
-                         " for pid %d", tcp->pid);
-       else if (dwfl_report_end(ctx->dwfl, NULL, NULL) != 0)
-               error_msg("dwfl_report_end returned an error"
-                         " for pid %d: %s", tcp->pid, dwfl_errmsg(-1));
-}
-
 const struct unwind_unwinder_t unwinder = {
        .name = "libdw",
-       .init = NULL,
+       .init = init,
        .tcb_init = tcb_init,
        .tcb_fin = tcb_fin,
        .tcb_walk = tcb_walk,
-       .tcb_flush_cache = tcb_flush_cache,
 };

diff --git a/unwind-libunwind.c b/unwind-libunwind.c
index 38b3e2c5921a6e7e3a57349275bb2c4d945d2cf3..c64e92cb7cf2dc0b15b77f0ae4616bf16e90e093 100644 (file)
--- a/unwind-libunwind.c
+++ b/unwind-libunwind.c
@@ -36,6 +36,8 @@ static unw_addr_space_t libunwind_as;
 static void
 init(void)
 {
+       mmap_cache_enable();
+
        libunwind_as = unw_create_addr_space(&_UPT_accessors, 0);
        if (!libunwind_as)
                error_msg_and_die("failed to create address space"
@@ -125,10 +127,10 @@ print_stack_frame(struct tcb *tcp,
 }
 
 static void
-tcb_walk(struct tcb *tcp,
-        unwind_call_action_fn call_action,
-        unwind_error_action_fn error_action,
-        void *data)
+walk(struct tcb *tcp,
+     unwind_call_action_fn call_action,
+     unwind_error_action_fn error_action,
+     void *data)
 {
        char *symbol_name;
        size_t symbol_name_size = 40;
@@ -159,9 +161,27 @@ tcb_walk(struct tcb *tcp,
 }
 
 static void
-tcb_flush_cache(struct tcb *tcp)
+tcb_walk(struct tcb *tcp,
+        unwind_call_action_fn call_action,
+        unwind_error_action_fn error_action,
+        void *data)
 {
-       unw_flush_cache(libunwind_as, 0, 0);
+       switch (mmap_cache_rebuild_if_invalid(tcp, __func__)) {
+               case MMAP_CACHE_REBUILD_RENEWED:
+                       /*
+                        * Rebuild the unwinder internal cache.
+                        * Called when mmap cache subsystem detects a
+                        * change of tracee memory mapping.
+                        */
+                       unw_flush_cache(libunwind_as, 0, 0);
+                       ATTRIBUTE_FALLTHROUGH;
+               case MMAP_CACHE_REBUILD_READY:
+                       walk(tcp, call_action, error_action, data);
+                       break;
+               default:
+                       /* Do nothing */
+                       ;
+       }
 }
 
 const struct unwind_unwinder_t unwinder = {
@@ -170,5 +190,4 @@ const struct unwind_unwinder_t unwinder = {
        .tcb_init = tcb_init,
        .tcb_fin = tcb_fin,
        .tcb_walk = tcb_walk,
-       .tcb_flush_cache = tcb_flush_cache,
 };

diff --git a/unwind.c b/unwind.c
index 586f74500b8bbae053a39d76bfcc7a9ee6c86a67..e4c6623c25fa376581a6cfa75be1bbfc49c37cf4 100644 (file)
--- a/unwind.c
+++ b/unwind.c
@@ -26,7 +26,6 @@
  */
 
 #include "defs.h"
-#include "mmap_cache.h"
 #include "unwind.h"
 
 #ifdef USE_DEMANGLE
@@ -59,7 +58,6 @@ unwind_init(void)
 {
        if (unwinder.init)
                unwinder.init();
-       mmap_cache_enable();
 }
 
 void
@@ -296,19 +294,8 @@ unwind_tcb_print(struct tcb *tcp)
                debug_func_msg("head: tcp=%p, queue=%p",
                               tcp, tcp->unwind_queue->head);
                queue_print(tcp->unwind_queue);
-       } else switch (mmap_cache_rebuild_if_invalid(tcp, __func__)) {
-               case MMAP_CACHE_REBUILD_RENEWED:
-                       unwinder.tcb_flush_cache(tcp);
-                       ATTRIBUTE_FALLTHROUGH;
-               case MMAP_CACHE_REBUILD_READY:
-                       debug_func_msg("walk: tcp=%p, queue=%p",
-                                      tcp, tcp->unwind_queue->head);
-                       unwinder.tcb_walk(tcp, print_call_cb, print_error_cb, NULL);
-                       break;
-               default:
-                       /* Do nothing */
-                       ;
-       }
+       } else
+               unwinder.tcb_walk(tcp, print_call_cb, print_error_cb, NULL);
 }
 
 /*
@@ -325,19 +312,10 @@ unwind_tcb_capture(struct tcb *tcp)
 #endif
        if (tcp->unwind_queue->head)
                error_msg_and_die("bug: unprinted entries in queue");
-
-       switch (mmap_cache_rebuild_if_invalid(tcp, __func__)) {
-       case MMAP_CACHE_REBUILD_RENEWED:
-               unwinder.tcb_flush_cache(tcp);
-               ATTRIBUTE_FALLTHROUGH;
-       case MMAP_CACHE_REBUILD_READY:
-               unwinder.tcb_walk(tcp, queue_put_call, queue_put_error,
-                                  tcp->unwind_queue);
-               debug_func_msg("tcp=%p, queue=%p",
+       else {
+               debug_func_msg("walk: tcp=%p, queue=%p",
                               tcp, tcp->unwind_queue->head);
-               break;
-       default:
-               /* Do nothing */
-               ;
+               unwinder.tcb_walk(tcp, queue_put_call, queue_put_error,
+                                 tcp->unwind_queue);
        }
 }

diff --git a/unwind.h b/unwind.h
index 3a6065b4dca53081b81a7aefe153331e935b2d25..678c561f71495316fd8a517552a4d2331973ac65 100644 (file)
--- a/unwind.h
+++ b/unwind.h
@@ -63,12 +63,6 @@ struct unwind_unwinder_t {
                           unwind_call_action_fn,
                           unwind_error_action_fn,
                           void *);
-
-       /*
-        * Rebuild the unwinder internal cache.  Called when mmap cache
-        * subsystem detects a change of tracee memory mapping.
-        */
-       void   (*tcb_flush_cache)(struct tcb *);
 };
 
 extern const struct unwind_unwinder_t unwinder;