Re: [PATCH] multithreaded coredumps for elf exeecutables for O(1) scheduler

[Vamsi Krishna S.]

Hi Mark,

Despite other problems with ia64, stopping vm ops after the status (regs) of
all the threads is captured, is a bug fix in generic code, and our
patch effectively nukes that. Not a good thing. I had posted a patch on top
of the previous tcore patch to fix this, I suppose it still applies to the
2.5.x patch. Please apply that (given here).

Vamsi.

Vamsi Krishna S.
Linux Technology Center,
IBM Software Lab, Bangalore.
Ph: [phone] Extn: 3959
Internet: [e-mail]

--- 2417-tcore/fs/binfmt_elf.c.ori	Thu Mar 21 15:30:08 2002
+++ 2417-tcore/fs/binfmt_elf.c	Thu Mar 21 15:27:29 2002
@@ -1289,10 +1289,6 @@
 	int dump_threads = 0;
 	int thread_status_size = 0;
 	
-	/* now stop all vm operations */
-	down_write(&current->mm->mmap_sem);
-	segs = current->mm->map_count;
-
  	if (atomic_read(&current->mm->mm_users) != 1) {
 		dump_threads = core_dumps_threads;
 	}
@@ -1337,6 +1333,19 @@
 		}
 	} /* End if(dump_threads) */
 
+	/*
+	 * This transfers the registers from regs into the standard
+	 * coredump arrangement, whatever that is. We need to do this
+	 * before acquiring mmap_sem as on some architectures (IA64)
+	 * we may need to access user pages to get register state.
+	 */
+	memset(&prstatus, 0, sizeof(prstatus));
+	elf_core_copy_regs(&prstatus.pr_reg, regs);
+
+	/* now stop all vm operations */
+	down_write(&current->mm->mmap_sem);
+	segs = current->mm->map_count;
+
 #ifdef DEBUG
 	printk("elf_core_dump: %d segs %lu limit\n", segs, limit);
 #endif
@@ -1358,16 +1367,9 @@
 	 * Set up the notes in similar form to SVR4 core dumps made
 	 * with info from their /proc.
 	 */
-	memset(&prstatus, 0, sizeof(prstatus));
 	fill_prstatus(&prstatus, current, signr);
 	fill_note(&notes[0], "CORE", NT_PRSTATUS, sizeof(prstatus), &prstatus);
 
-	/*
-	 * This transfers the registers from regs into the standard
-	 * coredump arrangement, whatever that is.
-	 */
-	elf_core_copy_regs(&prstatus.pr_reg, regs);
-
 #ifdef DEBUG
 	dump_regs("Passed in regs", (elf_greg_t *)regs);
 	dump_regs("prstatus regs", (elf_greg_t *)&prstatus.pr_reg);

On Fri, 10 May 2002 23:46:59 +0530, Mark Gross wrote:

> ia64 requires more tweaks than just this to work.  This patch as it stands isn't
> expected to work for ia64.
> 
> Getting the register states for the note sections is more involved for ia64 as
> well as the avoiding of patch collisions with  the diffs in
> /pub/linux/kernel/ports/ia64/v2.5/
> 
> I have an ia64 patch set thats partially tested for 2.4.17, that seems to work.
> It didn't get posted as O(1) support became a bigger priority.
> 
> I'm hoping to start updating the ia64 patch to support 2.5x very soon.
> 
> --mgross
> 
> On Friday 10 May 2002 01:13 pm, Manfred Spraul wrote:
>> Have you checked that your patch doesn't deadlock on ia64?
>>
>> > +       /* First pause all related threaded processes */ +       if
>> > (dump_threads)       {
>> > +               suspend_threads();
>> > +       }
>> > +
>> > +       /* now stop all vm operations */
>> > +       down_write(&current->mm->mmap_sem); +       segs =
>> > current->mm->map_count;
>> > +
>>
>> Stopping all vm operations means that copy_{to,from}_user can cause deadlocks.
>> ia64 needs copy_to_user in their stack unwind handler, IIRC called by
>> ELF_CORE_COPY_REGS.
>>
>> Afaics you don't handle that. You must dump all thread state before
>> down_write(mmap_sem). And I don't see how you protect against 2 threads of one
>> process calling suspend_threads() simultaneously.
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the
> body of a message to [e-mail] More majordomo info at
> http://vger.kernel.org/majordomo-info.html Please read the FAQ at
> http://www.tux.org/lkml/