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Dmitry Adamushko authoredThe problem occurs [1] when a kernel-mode task returns from a system call with a pending signal. A real-life scenario is a child of 'khelper' returning from a failed kernel_execve() in ____call_usermodehelper() [ kernel/kmod.c ]. kernel_execve() fails due to a pending SIGKILL, which is the result of "kill -9 -1" (at least, busybox's init does it upon reboot). The loop is as follows: * syscall_exit_work: - work_pending: // start_of_the_loop - work_notifysig: - do_notify_resume() - do_signal() - if (!user_mode(regs)) return; - resume_userspace // TIF_SIGPENDING is still set - work_pending // so we call work_pending => goto // start_of_the_loop More information can be found in another LKML thread: http://www.serverphorums.com/read.php?12,457826 [1] The problem was also reproduced on !CONFIG_VM86 x86, and the following fix was accepted. http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=29a2e2836ff9ea65a603c89df217f4198973a74f Signed-off-by:
Dmitry Adamushko <dmitry.adamushko@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3571/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>Dmitry Adamushko authoredThe problem occurs [1] when a kernel-mode task returns from a system call with a pending signal. A real-life scenario is a child of 'khelper' returning from a failed kernel_execve() in ____call_usermodehelper() [ kernel/kmod.c ]. kernel_execve() fails due to a pending SIGKILL, which is the result of "kill -9 -1" (at least, busybox's init does it upon reboot). The loop is as follows: * syscall_exit_work: - work_pending: // start_of_the_loop - work_notifysig: - do_notify_resume() - do_signal() - if (!user_mode(regs)) return; - resume_userspace // TIF_SIGPENDING is still set - work_pending // so we call work_pending => goto // start_of_the_loop More information can be found in another LKML thread: http://www.serverphorums.com/read.php?12,457826 [1] The problem was also reproduced on !CONFIG_VM86 x86, and the following fix was accepted. http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=29a2e2836ff9ea65a603c89df217f4198973a74f Signed-off-by:Dmitry Adamushko <dmitry.adamushko@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3571/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
entry.S 4.81 KiB
/*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*
* Copyright (C) 1994 - 2000, 2001, 2003 Ralf Baechle
* Copyright (C) 1999, 2000 Silicon Graphics, Inc.
* Copyright (C) 2001 MIPS Technologies, Inc.
*/
#include <asm/asm.h>
#include <asm/asmmacro.h>
#include <asm/regdef.h>
#include <asm/mipsregs.h>
#include <asm/stackframe.h>
#include <asm/isadep.h>
#include <asm/thread_info.h>
#include <asm/war.h>
#ifdef CONFIG_MIPS_MT_SMTC
#include <asm/mipsmtregs.h>
#endif
#ifndef CONFIG_PREEMPT
#define resume_kernel restore_all
#else
#define __ret_from_irq ret_from_exception
#endif
.text
.align 5
#ifndef CONFIG_PREEMPT
FEXPORT(ret_from_exception)
local_irq_disable # preempt stop
b __ret_from_irq
#endif
FEXPORT(ret_from_irq)
LONG_S s0, TI_REGS($28)
FEXPORT(__ret_from_irq)
/*
* We can be coming here from a syscall done in the kernel space,
* e.g. a failed kernel_execve().
*/
resume_userspace_check:
LONG_L t0, PT_STATUS(sp) # returning to kernel mode?
andi t0, t0, KU_USER
beqz t0, resume_kernel
resume_userspace:
local_irq_disable # make sure we dont miss an
# interrupt setting need_resched
# between sampling and return
LONG_L a2, TI_FLAGS($28) # current->work
andi t0, a2, _TIF_WORK_MASK # (ignoring syscall_trace)
bnez t0, work_pending
j restore_all
#ifdef CONFIG_PREEMPT
resume_kernel:
local_irq_disable
lw t0, TI_PRE_COUNT($28)
bnez t0, restore_all
need_resched:
LONG_L t0, TI_FLAGS($28)
andi t1, t0, _TIF_NEED_RESCHED
beqz t1, restore_all
LONG_L t0, PT_STATUS(sp) # Interrupts off?
andi t0, 1
beqz t0, restore_all
jal preempt_schedule_irq
b need_resched#endif
FEXPORT(ret_from_fork)
jal schedule_tail # a0 = struct task_struct *prev
FEXPORT(syscall_exit)
local_irq_disable # make sure need_resched and
# signals dont change between
# sampling and return
LONG_L a2, TI_FLAGS($28) # current->work
li t0, _TIF_ALLWORK_MASK
and t0, a2, t0
bnez t0, syscall_exit_work
restore_all: # restore full frame
#ifdef CONFIG_MIPS_MT_SMTC
#ifdef CONFIG_MIPS_MT_SMTC_IM_BACKSTOP
/* Re-arm any temporarily masked interrupts not explicitly "acked" */
mfc0 v0, CP0_TCSTATUS
ori v1, v0, TCSTATUS_IXMT
mtc0 v1, CP0_TCSTATUS
andi v0, TCSTATUS_IXMT
_ehb
mfc0 t0, CP0_TCCONTEXT
DMT 9 # dmt t1
jal mips_ihb
mfc0 t2, CP0_STATUS
andi t3, t0, 0xff00
or t2, t2, t3
mtc0 t2, CP0_STATUS
_ehb
andi t1, t1, VPECONTROL_TE
beqz t1, 1f
EMT
1:
mfc0 v1, CP0_TCSTATUS
/* We set IXMT above, XOR should clear it here */
xori v1, v1, TCSTATUS_IXMT
or v1, v0, v1
mtc0 v1, CP0_TCSTATUS
_ehb
xor t0, t0, t3
mtc0 t0, CP0_TCCONTEXT
#endif /* CONFIG_MIPS_MT_SMTC_IM_BACKSTOP */
/* Detect and execute deferred IPI "interrupts" */
LONG_L s0, TI_REGS($28)
LONG_S sp, TI_REGS($28)
jal deferred_smtc_ipi
LONG_S s0, TI_REGS($28)
#endif /* CONFIG_MIPS_MT_SMTC */
.set noat
RESTORE_TEMP
RESTORE_AT
RESTORE_STATIC
restore_partial: # restore partial frame
#ifdef CONFIG_TRACE_IRQFLAGS
SAVE_STATIC
SAVE_AT
SAVE_TEMP
LONG_L v0, PT_STATUS(sp)
#if defined(CONFIG_CPU_R3000) || defined(CONFIG_CPU_TX39XX)
and v0, ST0_IEP
#else
and v0, ST0_IE
#endif
beqz v0, 1f
jal trace_hardirqs_on
b 2f
1: jal trace_hardirqs_off
2: RESTORE_TEMP
RESTORE_AT
RESTORE_STATIC
#endif
RESTORE_SOME
RESTORE_SP_AND_RET
.set at
work_pending:
andi t0, a2, _TIF_NEED_RESCHED # a2 is preloaded with TI_FLAGS
beqz t0, work_notifysig
work_resched:
jal schedule
local_irq_disable # make sure need_resched and
# signals dont change between
# sampling and return
LONG_L a2, TI_FLAGS($28)
andi t0, a2, _TIF_WORK_MASK # is there any work to be done
# other than syscall tracing?
beqz t0, restore_all
andi t0, a2, _TIF_NEED_RESCHED
bnez t0, work_resched
work_notifysig: # deal with pending signals and
# notify-resume requests
move a0, sp
li a1, 0
jal do_notify_resume # a2 already loaded
j resume_userspace_check
FEXPORT(syscall_exit_partial)
local_irq_disable # make sure need_resched doesn't
# change between and return
LONG_L a2, TI_FLAGS($28) # current->work
li t0, _TIF_ALLWORK_MASK
and t0, a2
beqz t0, restore_partial
SAVE_STATIC
syscall_exit_work:
LONG_L t0, PT_STATUS(sp) # returning to kernel mode?
andi t0, t0, KU_USER
beqz t0, resume_kernel
li t0, _TIF_WORK_SYSCALL_EXIT
and t0, a2 # a2 is preloaded with TI_FLAGS
beqz t0, work_pending # trace bit set?
local_irq_enable # could let syscall_trace_leave()
# call schedule() instead
move a0, sp
jal syscall_trace_leave
b resume_userspace
#if defined(CONFIG_CPU_MIPSR2) || defined(CONFIG_MIPS_MT)
/*
* MIPS32R2 Instruction Hazard Barrier - must be called
*
* For C code use the inline version named instruction_hazard().
*/
LEAF(mips_ihb)
.set mips32r2
jr.hb ra
nop
END(mips_ihb)
#endif /* CONFIG_CPU_MIPSR2 or CONFIG_MIPS_MT */