linux-kernel - Re: [PATCH][CFT] [coredump] don't use __kernel_write() on kmap_local

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Date:   Mon, 3 Oct 2022 12:31:36 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     "J. R. Okajima" <hooanon05g@...il.com>
CC:     Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH][CFT] [coredump] don't use __kernel_write() on
 kmap_local_page()

On Mon, Oct 03, 2022 at 07:48:28PM +0900, J. R. Okajima wrote:
> Ira Weiny:
> > On Wed, Sep 28, 2022 at 07:29:43PM +0100, Al Viro wrote:
> > > On Tue, Sep 27, 2022 at 11:51:17PM +0100, Al Viro wrote:
> > > > [I'm going to send a pull request tomorrow if nobody yells;
> > > > please review and test - it seems to work fine here, but extra
> > > > eyes and extra testing would be very welcome]
> 
> I tried gdb backtrace 'bt' command with the new core by v6.0, and it
> doesn't show the call trace correctly. Is it related to this commit?
>

Are you also getting something like this?

BFD: warning: /mnt/9p/test-okajima/core is truncated: expected core file size >= 225280, found: 76616

I did not see that before.  I'm running through this patch vs a fix to
kmap_to_page()[1] and I may have gotten the 2 crossed up.  So I'm retesting
with your test below.

Ira

[1] https://lore.kernel.org/linux-mm/20221003040427.1082050-1-ira.weiny@intel.com/
 
> test program
> ----------------------------------------
> void f(int n)
> {
> 	printf("%d\n", n);
> 	if (!n)
> 		kill(getpid(), SIGQUIT);
> 	f(--n);
> }
> 
> int main(int argc, char *argv[])
> {
> 	f(atoi(argv[1]));
> 	return 0;
> }
> ----------------------------------------
> ulimit -c unlimited
> coredump 2
> gdb coredump core
> bt
> ----------------------------------------
> expected result
> kill
> f
> f
> f
> main
> ----------------------------------------
> actual result
> ??
> ??
> ----------------------------------------
> 
> 
> J. R. Okajima