um: Revert to using stack for pt_regs in signal handling

Reverts commit b6024b21fec8367ef961a771cc9dde31f1831965 and
adjusts default stack sizing to cope with larger size of
floating point save registers on the newer Intel CPUs.

b6024b21fec8367ef961a771cc9dde31f1831965 replaced storing the
register state on the stack with kmalloc-ed storage. That has
a number of issues and a panic if that fails.
    1. kmalloc/ATOMIC can fail. There was a latent hard crash
in all interrupt and fault handling as a result.
    2. kmalloc in the interrupt path introduces a considerable
performance penalty for networking ~ 14% on iperf.

This commit restores uml to a stable state until a better
solution is found.

Signed-off-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

1 files changed, 8 insertions, 20 deletions

diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index bf0acb8aad8b..75b10235d369 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -31,29 +31,23 @@ void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
 
 static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
 {
-	struct uml_pt_regs *r;
+	struct uml_pt_regs r;
 	int save_errno = errno;
 
-	r = uml_kmalloc(sizeof(struct uml_pt_regs), UM_GFP_ATOMIC);
-	if (!r)
-		panic("out of memory");
-
-	r->is_user = 0;
+	r.is_user = 0;
 	if (sig == SIGSEGV) {
 		/* For segfaults, we want the data from the sigcontext. */
-		get_regs_from_mc(r, mc);
-		GET_FAULTINFO_FROM_MC(r->faultinfo, mc);
+		get_regs_from_mc(&r, mc);
+		GET_FAULTINFO_FROM_MC(r.faultinfo, mc);
 	}
 
 	/* enable signals if sig isn't IRQ signal */
 	if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGALRM))
 		unblock_signals();
 
-	(*sig_info[sig])(sig, si, r);
+	(*sig_info[sig])(sig, si, &r);
 
 	errno = save_errno;
-
-	free(r);
 }
 
 /*
@@ -91,17 +85,11 @@ void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
 
 static void timer_real_alarm_handler(mcontext_t *mc)
 {
-	struct uml_pt_regs *regs;
-
-	regs = uml_kmalloc(sizeof(struct uml_pt_regs), UM_GFP_ATOMIC);
-	if (!regs)
-		panic("out of memory");
+	struct uml_pt_regs regs;
 
 	if (mc != NULL)
-		get_regs_from_mc(regs, mc);
-	timer_handler(SIGALRM, NULL, regs);
-
-	free(regs);
+		get_regs_from_mc(&regs, mc);
+	timer_handler(SIGALRM, NULL, &regs);
 }
 
 void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)