coredump: construct the list of coredumping threads at startup time

binfmt->core_dump() has to iterate over the all threads in system in order
to find the coredumping threads and construct the list using the
GFP_ATOMIC allocations.

With this patch each thread allocates the list node on exit_mm()'s stack and
adds itself to the list.

This allows us to do further changes:

	- simplify ->core_dump()

	- change exit_mm() to clear ->mm first, then wait for ->core_done.
	  this makes the coredumping process visible to oom_kill

	- kill mm->core_done

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

diff --git a/fs/exec.c b/fs/exec.c
index b8ee842..fe2873b 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1604,6 +1604,8 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
 
        init_completion(&mm->core_done);
        init_completion(&core_state->startup);
+       core_state->dumper.task = tsk;
+       core_state->dumper.next = NULL;
        core_waiters = zap_threads(tsk, mm, core_state, exit_code);
        up_write(&mm->mmap_sem);
 

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index ae99a28..4d0d0ab 100644 (file)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -159,8 +159,14 @@ struct vm_area_struct {
 #endif
 };
 
+struct core_thread {
+       struct task_struct *task;
+       struct core_thread *next;
+};
+
 struct core_state {
        atomic_t nr_threads;
+       struct core_thread dumper;
        struct completion startup;
 };
 

diff --git a/kernel/exit.c b/kernel/exit.c
index 63d8295..b66f0d5 100644 (file)
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -664,6 +664,7 @@ assign_new_owner:
 static void exit_mm(struct task_struct * tsk)
 {
        struct mm_struct *mm = tsk->mm;
+       struct core_state *core_state;
 
        mm_release(tsk, mm);
        if (!mm)
@@ -676,11 +677,19 @@ static void exit_mm(struct task_struct * tsk)
         * group with ->mm != NULL.
         */
        down_read(&mm->mmap_sem);
-       if (mm->core_state) {
+       core_state = mm->core_state;
+       if (core_state) {
+               struct core_thread self;
                up_read(&mm->mmap_sem);
 
-               if (atomic_dec_and_test(&mm->core_state->nr_threads))
-                       complete(&mm->core_state->startup);
+               self.task = tsk;
+               self.next = xchg(&core_state->dumper.next, &self);
+               /*
+                * Implies mb(), the result of xchg() must be visible
+                * to core_state->dumper.
+                */
+               if (atomic_dec_and_test(&core_state->nr_threads))
+                       complete(&core_state->startup);
 
                wait_for_completion(&mm->core_done);
                down_read(&mm->mmap_sem);