From 5c2ffce1e9496477720966e70d79f2da3e4b84e6 Mon Sep 17 00:00:00 2001 From: Anton Ivanov Date: Fri, 4 Jan 2019 15:38:21 +0000 Subject: [PATCH] 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 Signed-off-by: Richard Weinberger --- arch/um/Kconfig | 10 +++++++--- arch/um/os-Linux/signal.c | 28 ++++++++-------------------- 2 files changed, 15 insertions(+), 23 deletions(-) diff --git a/arch/um/Kconfig b/arch/um/Kconfig index ec9711d..4191350 100644 --- a/arch/um/Kconfig +++ b/arch/um/Kconfig @@ -142,13 +142,17 @@ config MAGIC_SYSRQ config KERNEL_STACK_ORDER int "Kernel stack size order" - default 1 if 64BIT - range 1 10 if 64BIT - default 0 if !64BIT + default 2 if 64BIT + range 2 10 if 64BIT + default 1 if !64BIT help This option determines the size of UML kernel stacks. They will be 1 << order pages. The default is OK unless you're running Valgrind on UML, in which case, set this to 3. + It is possible to reduce the stack to 1 for 64BIT and 0 for 32BIT on + older (pre-2017) CPUs. It is not recommended on newer CPUs due to the + increase in the size of the state which needs to be saved when handling + signals. config MMAPPER tristate "iomem emulation driver" diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c index bf0acb8..75b1023 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(®s, mc); + timer_handler(SIGALRM, NULL, ®s); } void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc) -- 2.7.4