[DragonFlyBSD - Bug #3318] (In Progress) Segmenation fault when a process resumed with checkpt exits

[bugtracker-admin at leaf.dragonflybsd.org]

Issue #3318 has been updated by tuxillo.

Status changed from New to In Progress
Assignee set to tuxillo
Target version set to 6.4

Back in the day we added two memory mappable devices (/dev/upmap and /dev/kpmap) which provide certain data from the kernel without the need of a system call. See commit:0adbcbd6bc12ddb.
One is per-thread and the other isn't.

The thing is that we need to add handling for the one which isn't per-thread, since sys_checkpoint(2) and checkpt(1) does not support threaded programs, as stated in the manpage:

>> Threaded programs cannot currently be checkpointed.  The program must be reduced to a single thread before it can be safely checkpointed.

See: https://man.dragonflybsd.org/?command=sys_checkpoint

We'll try t at least handle that case but we're also considering how useful process checkpointing really is. If anybody has any feedback about it now it would be the time to share it :-)

----------------------------------------
Bug #3318: Segmenation fault when a process resumed with checkpt exits
http://bugs.dragonflybsd.org/issues/3318#change-14384

* Author: zabolekar
* Status: In Progress
* Priority: Normal
* Assignee: tuxillo
* Target version: 6.4
* Start date: 2022-06-12
----------------------------------------
DragonFly version: 6.2.1

Code example (error handling omitted for brevity):
<pre><code class="c">
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/checkpoint.h>
     
void save(const char* filename)
{
    int file = open(filename, O_RDWR|O_CREAT|O_TRUNC, 0666);
    sys_checkpoint(CKPT_FREEZE, file, -1, -1);
    close(file);
}
  
int main()
{
    puts("a");
    save("a.ckpt");
    puts("b");
}
</code></pre>

Expected output:

<pre>
% gcc test.c -o test -Wall -Wextra
% ./test
a
b
% checkpt -r a.ckpt
b
</pre>

Actual output:

<pre>
% gcc test.c -o test -Wall -Wextra
% ./test
a
b
% checkpt -r a.ckpt
b
pid 1143 (test), uid 1001: exited on signal 11 (core dumped)
Segmentation fault (core dumped)
</pre>

Backtrace with @gdb test test.core@:

<pre>
#0  0x000000080040400f in __tls_get_addr () from /libexec/ld-elf.so.2
#1  0x000000080075648a in _thread_finalize () from /lib/libc.so.8
#2  0x0000000800756449 in exit () from /lib/libc.so.8
#3  0x00000000004007b3 in _start ()
</pre>

See also: https://lists.dragonflybsd.org/pipermail/users/2022-June/405002.html



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