coredump: move mm->core_waiters into struct core_state

Move mm->core_waiters into "struct core_state" allocated on stack.  This
shrinks mm_struct a little bit and allows further changes.

This patch mostly does s/core_waiters/core_state.  The only essential
change is that coredump_wait() must clear mm->core_state before return.

The coredump_wait()'s path is uglified and .text grows by 30 bytes, this
is fixed by the next patch.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 19 insertions, 18 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 71734568f018..50de3aaff4d0 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -722,12 +722,10 @@ static int exec_mmap(struct mm_struct *mm)
                  * Make sure that if there is a core dump in progress
                  * for the old mm, we get out and die instead of going
                  * through with the exec.  We must hold mmap_sem around
-                 * checking core_waiters and changing tsk->mm.  The
-                 * core-inducing thread will increment core_waiters for
-                 * each thread whose ->mm == old_mm.
+                 * checking core_state and changing tsk->mm.
                  */
                 down_read(&old_mm->mmap_sem);
-                if (unlikely(old_mm->core_waiters)) {
+                if (unlikely(old_mm->core_state)) {
                         up_read(&old_mm->mmap_sem);
                         return -EINTR;
                 }
@@ -1514,7 +1512,7 @@ static void zap_process(struct task_struct *start)
         t = start;
         do {
                 if (t != current && t->mm) {
-                        t->mm->core_waiters++;
+                        t->mm->core_state->nr_threads++;
                         sigaddset(&t->pending.signal, SIGKILL);
                         signal_wake_up(t, 1);
                 }
@@ -1538,11 +1536,11 @@ static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
         if (err)
                 return err;
 
-        if (atomic_read(&mm->mm_users) == mm->core_waiters + 1)
+        if (atomic_read(&mm->mm_users) == mm->core_state->nr_threads + 1)
                 goto done;
         /*
          * We should find and kill all tasks which use this mm, and we should
-         * count them correctly into mm->core_waiters. We don't take tasklist
+         * count them correctly into ->nr_threads. We don't take tasklist
          * lock, but this is safe wrt:
          *
          * fork:
@@ -1590,7 +1588,7 @@ static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
         }
         rcu_read_unlock();
 done:
-        return mm->core_waiters;
+        return mm->core_state->nr_threads;
 }
 
 static int coredump_wait(int exit_code)
@@ -1603,9 +1601,12 @@ static int coredump_wait(int exit_code)
 
         init_completion(&mm->core_done);
         init_completion(&core_state.startup);
+        core_state.nr_threads = 0;
         mm->core_state = &core_state;
 
         core_waiters = zap_threads(tsk, mm, exit_code);
+        if (core_waiters < 0)
+                mm->core_state = NULL;
         up_write(&mm->mmap_sem);
 
         if (unlikely(core_waiters < 0))
@@ -1623,8 +1624,8 @@ static int coredump_wait(int exit_code)
 
         if (core_waiters)
                 wait_for_completion(&core_state.startup);
+        mm->core_state = NULL;
 fail:
-        BUG_ON(mm->core_waiters);
         return core_waiters;
 }
 
@@ -1702,7 +1703,7 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
         /*
          * If another thread got here first, or we are not dumpable, bail out.
          */
-        if (mm->core_waiters || !get_dumpable(mm)) {
+        if (mm->core_state || !get_dumpable(mm)) {
                 up_write(&mm->mmap_sem);
                 goto fail;
         }
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 97819efd2333..c0b1747b61a5 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -160,6 +160,7 @@ struct vm_area_struct {
 };
 
 struct core_state {
+        int nr_threads;
         struct completion startup;
 };
 
@@ -179,7 +180,6 @@ struct mm_struct {
         atomic_t mm_users;                      /* How many users with user space? */
         atomic_t mm_count;                      /* How many references to "struct mm_struct" (users count as 1) */
         int map_count;                          /* number of VMAs */
-        int core_waiters;
         struct rw_semaphore mmap_sem;
         spinlock_t page_table_lock;             /* Protects page tables and some counters */
 
diff --git a/kernel/exit.c b/kernel/exit.c
index f7fa21dbced4..988e232254e9 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -670,16 +670,16 @@ static void exit_mm(struct task_struct * tsk)
                 return;
         /*
          * Serialize with any possible pending coredump.
-         * We must hold mmap_sem around checking core_waiters
+         * We must hold mmap_sem around checking core_state
          * and clearing tsk->mm.  The core-inducing thread
-         * will increment core_waiters for each thread in the
+         * will increment ->nr_threads for each thread in the
          * group with ->mm != NULL.
          */
         down_read(&mm->mmap_sem);
-        if (mm->core_waiters) {
+        if (mm->core_state) {
                 up_read(&mm->mmap_sem);
                 down_write(&mm->mmap_sem);
-                if (!--mm->core_waiters)
+                if (!--mm->core_state->nr_threads)
                         complete(&mm->core_state->startup);
                 up_write(&mm->mmap_sem);
 
diff --git a/kernel/fork.c b/kernel/fork.c
index eeaec6893b0d..813d5c89b9d5 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -400,7 +400,7 @@ static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
         INIT_LIST_HEAD(&mm->mmlist);
         mm->flags = (current->mm) ? current->mm->flags
                                   : MMF_DUMP_FILTER_DEFAULT;
-        mm->core_waiters = 0;
+        mm->core_state = NULL;
         mm->nr_ptes = 0;
         set_mm_counter(mm, file_rss, 0);
         set_mm_counter(mm, anon_rss, 0);
diff --git a/kernel/signal.c b/kernel/signal.c
index 39c1706edf03..5c7b7eaa0dc6 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1480,10 +1480,10 @@ static inline int may_ptrace_stop(void)
          * is a deadlock situation, and pointless because our tracer
          * is dead so don't allow us to stop.
          * If SIGKILL was already sent before the caller unlocked
-         * ->siglock we must see ->core_waiters != 0. Otherwise it
+         * ->siglock we must see ->core_state != NULL. Otherwise it
          * is safe to enter schedule().
          */
-        if (unlikely(current->mm->core_waiters) &&
+        if (unlikely(current->mm->core_state) &&
             unlikely(current->mm == current->parent->mm))
                 return 0;