My emacs problem -- was Re: [PATCH] x86/fpu: Use fault_in_pages_writeable() for pre-faulting

[Pavel Machek <pavel@ucw.cz>]

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Hi!

On Sun 2019-05-26 12:25:27, Hugh Dickins wrote:
> On Sun, 26 May 2019, Sebastian Andrzej Siewior wrote:
> > On 2019-05-26 19:33:25 [+0200], To Hugh Dickins wrote:
> > From: Hugh Dickins <hughd@google.com>
> > …
> > > Signed-off-by: Hugh Dickins <hughd@google.com>
> > 
> > Hugh, I took your patch, slapped a signed-off-by line. Please say that
> > you are fine with it (or object otherwise).
> 
> I'm fine with it, thanks Sebastian. Sorry if I wasted your time by not
> giving it my sign-off in the first place, but I was not comfortable to
> dabble there without your sign-off too - which it now has. (And thought
> you might already have your own version anyway: just provided mine as
> illustration, so that we could be sure of exactly what I'd been testing.)

I applied Hugh's patch on top of -rc2, but still get emacs problems:

But this time I'm not sure if it is same emacs problem or different
emacs problem....

X protocol error: BadValue (integer parameter out of range for
operation) on protocol request 139
When compiled with GTK, Emacs cannot recover from X disconnects.
This is a GTK bug: https://bugzilla.gnome.org/show_bug.cgi?id=85715
For details, see etc/PROBLEMS.

(emacs:8175): GLib-WARNING **: g_main_context_prepare() called
recursively from within a source's check() or prepare() member.

(emacs:8175): GLib-WARNING **: g_main_context_check() called
recursively from within a source's check() or prepare() member.
Fatal error 6: Aborted
Backtrace:
emacs[0x8138719]
emacs[0x8120446]
emacs[0x813875c]
emacs[0x80f54c0]
emacs[0x80f6f3f]
emacs[0x80f6fab]
/usr/lib/i386-linux-gnu/libX11.so.6(_XError+0x11a)[0xf6ea1b3a]
/usr/lib/i386-linux-gnu/libX11.so.6(+0x39b5b)[0xf6e9eb5b]
/usr/lib/i386-linux-gnu/libX11.so.6(+0x39c26)[0xf6e9ec26]
/usr/lib/i386-linux-gnu/libX11.so.6(_XEventsQueued+0x6e)[0xf6e9f4be]
/usr/lib/i386-linux-gnu/libX11.so.6(XPending+0x62)[0xf6e90752]
/usr/lib/i386-linux-gnu/libgdk-3.so.0(+0x48073)[0xf7566073]
/lib/i386-linux-gnu/libglib-2.0.so.0(g_main_context_prepare+0x17b)[0xf70244fb]
/lib/i386-linux-gnu/libglib-2.0.so.0(+0x46f74)[0xf7024f74]
/lib/i386-linux-gnu/libglib-2.0.so.0(g_main_context_pending+0x34)[0xf7025144]
/usr/lib/i386-linux-gnu/libgtk-3.so.0(gtk_events_pending+0x1f)[0xf77c9a8f]
emacs[0x80f55a9]
emacs[0x812714f]
emacs[0x8126a95]
emacs[0x8172db9]
emacs[0x8192bd7]
emacs[0x819312d]
emacs[0x8125634]
emacs[0x8125c6d]
emacs[0x812725b]
emacs[0x8129eaa]
emacs[0x81c7c90]
emacs[0x8127815]
emacs[0x812ada3]
emacs[0x812bdad]
emacs[0x812d838]
emacs[0x818b76c]
emacs[0x8120890]
emacs[0x818b66b]
emacs[0x8124b84]
emacs[0x8124e3f]
emacs[0x8059cb0]
/lib/i386-linux-gnu/i686/cmov/libc.so.6(__libc_start_main+0xf3)[0xf61a7a63]
emacs[0x805a76f]
Aborted (core dumped)

Best regards,
									Pavel


commit 018c9da72adf920efd0ba250fcf433b836d3cfbc
Author: Hugh Dickins <hughd@google.com>
Date:   Sun May 26 19:33:25 2019 +0200

    x86/fpu: Use fault_in_pages_writeable() for pre-faulting
    
    Since commit
    
       d9c9ce34ed5c8 ("x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails")
    
    we use get_user_pages_unlocked() to pre-faulting user's memory if a
    write generates a page fault while the handler is disabled.
    This works in general and uncovered a bug as reported by Mike Rapoport.
    
    It has been pointed out that this function may be fragile and a
    simple pre-fault as in fault_in_pages_writeable() would be a better
    solution. Better as in taste and simplicity: That write (as performed by
    the alternative function) performs exactly the same faulting of memory
    that we had before. This was suggested by Hugh Dickins and Andrew
    Morton.
    
    Use fault_in_pages_writeable() for pre-faulting of user's stack.
    
    Suggested-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Hugh Dickins <hughd@google.com>
    Link: https://lkml.kernel.org/r/alpine.LSU.2.11.1905251033230.1112@eggly.anvils
    [bigeasy: patch description]
    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 5a8d118..060d618 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -5,6 +5,7 @@
 
 #include <linux/compat.h>
 #include <linux/cpu.h>
+#include <linux/pagemap.h>
 
 #include <asm/fpu/internal.h>
 #include <asm/fpu/signal.h>
@@ -189,15 +190,7 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
 	fpregs_unlock();
 
 	if (ret) {
-		int aligned_size;
-		int nr_pages;
-
-		aligned_size = offset_in_page(buf_fx) + fpu_user_xstate_size;
-		nr_pages = DIV_ROUND_UP(aligned_size, PAGE_SIZE);
-
-		ret = get_user_pages_unlocked((unsigned long)buf_fx, nr_pages,
-					      NULL, FOLL_WRITE);
-		if (ret == nr_pages)
+		if (!fault_in_pages_writeable(buf_fx, fpu_user_xstate_size))
 			goto retry;
 		return -EFAULT;
 	}



-- 
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