linux-kernel - Re: [PATCH] coredump: elf_core

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Message-Id: <20080627204953.C2A49154224@magilla.localdomain>
Date:	Thu, 19 Jun 2008 00:19:32 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coredump: elf_core_dump: skip kernel threads

Perhaps a little prettier like this:

--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1469,6 +1469,12 @@ static int fill_thread_core_info(struct 
 	return 1;
 }
 
+static bool is_dump_thread(struct task_struct *dump_task,
+			   struct task_struct *thread)
+{
+	return !(thread->flags & PF_KTHREAD) && thread->mm == dump_task->mm;
+}
+
 static int fill_note_info(struct elfhdr *elf, int phdrs,
 			  struct elf_note_info *info,
 			  long signr, struct pt_regs *regs)
@@ -1518,7 +1524,7 @@ static int fill_note_info(struct elfhdr 
 	 */
 	rcu_read_lock();
 	do_each_thread(g, p)
-		if (p->mm == dump_task->mm) {
+		if (is_dump_thread(dump_task, p)) {
 			t = kzalloc(offsetof(struct elf_thread_core_info,
 					     notes[info->thread_notes]),
 				    GFP_ATOMIC);
@@ -1722,7 +1728,7 @@ static int fill_note_info(struct elfhdr 
 		struct elf_thread_status *ets;
 		rcu_read_lock();
 		do_each_thread(g, p)
-			if (current->mm == p->mm && current != p) {
+			if (p != current && is_dump_thread(current, p)) {
 				ets = kzalloc(sizeof(*ets), GFP_ATOMIC);
 				if (!ets) {
 					rcu_read_unlock();

Or maybe you'll have other reasons to add a task_user_mm() that returns
NULL for kthreads, and then just use task_user_mm(p) == dump_task->mm here.

> It is sad we have to iterate over all threads in system and use GFP_ATOMIC.
> Hopefully we can kill theses ugly do_each_thread()s, but this needs some
> nontrivial changes in mm_struct and do_coredump.

Agreed, and twice at that (coredump_wait).  But this is something more to
consider for the future, and I wouldn't worry about it right now.


Thanks,
Roland
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