在 2024/3/4 19:56, David Howells 写道:
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
Actually, I think the right model is to get rid of that horrendous
.copy_mc field entirely.
We only have one single place that uses it - that nasty core dumping
code. And that code is *not* performance critical.
And not only isn't it performance-critical, it already does all the
core dumping one page at a time because it doesn't want to write pages
that were never mapped into user space.
So what we can do is
(a) make the core dumping code *copy* the page to a good location
with copy_mc_to_kernel() first
(b) remove this horrendous .copy_mc crap entirely from iov_iter
This is slightly complicated by the fact that copy_mc_to_kernel() may
not even exist, and architectures that don't have it don't want the
silly extra copy. So we need to abstract the "copy to temporary page"
code a bit. But that's probably a good thing anyway in that it forces
us to have nice interfaces.
End result: something like the attached.
AGAIN: THIS IS ENTIRELY UNTESTED.
But hey, so was clearly all the .copy_mc code too that this removes, so...
I like it:-)
I've tested it by SIGQUIT'ing a number of processes and using gdb to examine
the coredumps - which seems to work - at least without the production of any
MCEs. I'm not sure how I could test it with MCEs.
I'm going to test the coredump with the MCE.
Feel free to add:
Reviewed-by: David Howells <dhowells@xxxxxxxxxx>
Tested-by: David Howells <dhowells@xxxxxxxxxx>
That said, I wonder if:
#ifdef copy_mc_to_kernel
should be:
#ifdef CONFIG_ARCH_HAS_COPY_MC
and whether it's possible to find out dynamically if MCEs can occur at all.
MCE can occur during the use of a page. So i think it occurs
dynamically.
Thanks,
Tong
David
.
