tracepoint: Add signal coredump tracepoint

From: Masami Hiramatsu <mhiramat@redhat.com>

Add signal coredump tracepoint which shows signal number,
mm->flags, limits, pointer to file structure and core
file name.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
---

 fs/exec.c                     |   22 +++++++++++----------
 include/trace/events/signal.h |   43 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 10 deletions(-)


diff --git a/fs/exec.c b/fs/exec.c
index 2ec6973..56f512a 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -56,6 +56,7 @@
 #include <linux/fsnotify.h>
 #include <linux/fs_struct.h>
 #include <linux/pipe_fs_i.h>
+#include <trace/events/signal.h>
 
 #include <asm/uaccess.h>
 #include <asm/mmu_context.h>
@@ -1772,6 +1773,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
 	static atomic_t core_dump_count = ATOMIC_INIT(0);
 	struct coredump_params cprm = {
 		.signr = signr,
+		.file = NULL,
 		.regs = regs,
 		.limit = current->signal->rlim[RLIMIT_CORE].rlim_cur,
 		/*
@@ -1837,9 +1839,6 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
 	ispipe = format_corename(corename, signr);
 	unlock_kernel();
 
-	if ((!ispipe) && (cprm.limit < binfmt->min_coredump))
-		goto fail_unlock;
-
  	if (ispipe) {
 		if (cprm.limit == 0) {
 			/*
@@ -1860,7 +1859,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
 				"Process %d(%s) has RLIMIT_CORE set to 0\n",
 				task_tgid_vnr(current), current->comm);
 			printk(KERN_WARNING "Aborting core\n");
-			goto fail_unlock;
+			goto end_open;
 		}
 
 		dump_count = atomic_inc_return(&core_dump_count);
@@ -1868,14 +1867,14 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
 			printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n",
 			       task_tgid_vnr(current), current->comm);
 			printk(KERN_WARNING "Skipping core dump\n");
-			goto fail_dropcount;
+			goto end_open;
 		}
 
 		helper_argv = argv_split(GFP_KERNEL, corename+1, &helper_argc);
 		if (!helper_argv) {
 			printk(KERN_WARNING "%s failed to allocate memory\n",
 			       __func__);
-			goto fail_dropcount;
+			goto end_open;
 		}
 
 		cprm.limit = RLIM_INFINITY;
@@ -1885,13 +1884,17 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
 				&cprm.file)) {
  			printk(KERN_INFO "Core dump to %s pipe failed\n",
 			       corename);
-			goto fail_dropcount;
+			goto end_open;
  		}
- 	} else
+	} else if (cprm.limit >= binfmt->min_coredump)
 		cprm.file = filp_open(corename,
 				 O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
 				 0600);
-	if (IS_ERR(cprm.file))
+
+end_open:
+	trace_signal_coredump(&cprm, corename);
+
+	if (!cprm.file || IS_ERR(cprm.file))
 		goto fail_dropcount;
 	inode = cprm.file->f_path.dentry->d_inode;
 	if (inode->i_nlink > 1)
@@ -1928,7 +1931,6 @@ close_fail:
 fail_dropcount:
 	if (dump_count)
 		atomic_dec(&core_dump_count);
-fail_unlock:
 	if (helper_argv)
 		argv_free(helper_argv);
 
diff --git a/include/trace/events/signal.h b/include/trace/events/signal.h
index a510b75..7feba6e 100644
--- a/include/trace/events/signal.h
+++ b/include/trace/events/signal.h
@@ -6,6 +6,7 @@
 
 #include <linux/signal.h>
 #include <linux/sched.h>
+#include <linux/binfmts.h>
 #include <linux/tracepoint.h>
 
 #define TP_STORE_SIGINFO(__entry, info)				\
@@ -167,6 +168,48 @@ TRACE_EVENT(signal_lose_info,
 	TP_printk("sig=%d group=%d errno=%d code=%d",
 		  __entry->sig, __entry->group, __entry->errno, __entry->code)
 );
+
+/**
+ * signal_coredump - called when dumping core by signal
+ * @cprm: pointer to struct coredump_params
+ * @core_name: core-name string
+ *
+ * Current process dumps core file to 'core_name' file, because 'cprm->signr'
+ * signal is delivered.
+ * 'cprm->file' is a pointer to file structure of core file, if it is NULL
+ * or an error number(IS_ERR(cprm->file)), coredump should be failed.
+ */
+TRACE_EVENT(signal_coredump,
+
+	TP_PROTO(struct coredump_params *cprm, const char *core_name),
+
+	TP_ARGS(cprm, core_name),
+
+	TP_STRUCT__entry(
+		__field(	int,		sig		)
+		__field(	unsigned long,	limit		)
+		__field(	unsigned long,	flags		)
+		__field(	unsigned long,	file		)
+		__string(	name,		core_name	)
+	),
+
+
+	TP_fast_assign(
+		__entry->sig	= (int)cprm->signr;
+		__entry->limit	= cprm->limit;
+		__entry->flags	= cprm->mm_flags;
+		__entry->file	= (unsigned long)cprm->file;
+		__assign_str(name,	core_name);
+	),
+
+	TP_printk("sig=%d limit=%lu dumpable=%lx dump_filter=%lx "
+		  "file=%lx corename=%s",
+		  __entry->sig, __entry->limit,
+		  __entry->flags & MMF_DUMPABLE_MASK,
+		  (__entry->flags & MMF_DUMP_FILTER_MASK) >>
+		  MMF_DUMP_FILTER_SHIFT,
+		  __entry->file, __get_str(name))
+);
 #endif /* _TRACE_SIGNAL_H */
 
 /* This part must be outside protection */