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887c5c12e8
sched_yield by a userspace may not actually cause scheduling in time-travel mode as no time has passed. In the case seen it appears to be a badly implemented userspace spinlock in ASAN. Unfortunately, with time-travel it causes an extreme slowdown or even deadlock depending on the kernel configuration (CONFIG_UML_MAX_USERSPACE_ITERATIONS). Work around it by accounting time to the process whenever it executes a sched_yield syscall. Signed-off-by: Benjamin Berg <benjamin.berg@intel.com> Link: https://patch.msgid.link/20250314130815.226872-1-benjamin@sipsolutions.net Signed-off-by: Johannes Berg <johannes.berg@intel.com>
68 lines
1.7 KiB
C
68 lines
1.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
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*/
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#include <linux/kernel.h>
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#include <linux/ptrace.h>
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#include <linux/seccomp.h>
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#include <kern_util.h>
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#include <sysdep/ptrace.h>
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#include <sysdep/ptrace_user.h>
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#include <sysdep/syscalls.h>
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#include <linux/time-internal.h>
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#include <asm/unistd.h>
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#include <asm/delay.h>
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void handle_syscall(struct uml_pt_regs *r)
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{
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struct pt_regs *regs = container_of(r, struct pt_regs, regs);
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int syscall;
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/* Initialize the syscall number and default return value. */
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UPT_SYSCALL_NR(r) = PT_SYSCALL_NR(r->gp);
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PT_REGS_SET_SYSCALL_RETURN(regs, -ENOSYS);
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if (syscall_trace_enter(regs))
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goto out;
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/* Do the seccomp check after ptrace; failures should be fast. */
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if (secure_computing() == -1)
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goto out;
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syscall = UPT_SYSCALL_NR(r);
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/*
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* If no time passes, then sched_yield may not actually yield, causing
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* broken spinlock implementations in userspace (ASAN) to hang for long
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* periods of time.
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*/
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if ((time_travel_mode == TT_MODE_INFCPU ||
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time_travel_mode == TT_MODE_EXTERNAL) &&
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syscall == __NR_sched_yield)
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tt_extra_sched_jiffies += 1;
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if (syscall >= 0 && syscall < __NR_syscalls) {
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unsigned long ret = EXECUTE_SYSCALL(syscall, regs);
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PT_REGS_SET_SYSCALL_RETURN(regs, ret);
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/*
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* An error value here can be some form of -ERESTARTSYS
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* and then we'd just loop. Make any error syscalls take
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* some time, so that it won't just loop if something is
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* not ready, and hopefully other things will make some
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* progress.
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*/
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if (IS_ERR_VALUE(ret) &&
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(time_travel_mode == TT_MODE_INFCPU ||
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time_travel_mode == TT_MODE_EXTERNAL)) {
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um_udelay(1);
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schedule();
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}
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}
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out:
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syscall_trace_leave(regs);
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}
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