Commit 972410b0 authored by Paolo 'Blaisorblade' Giarrusso's avatar Paolo 'Blaisorblade' Giarrusso Committed by Linus Torvalds

[PATCH] uml: clean arch_switch usage

Call arch_switch also in switch_to_skas, even if it's, for now, a no-op for
that case (and mark this in the comment); this will change soon.

Also, arch_switch for TT mode is actually useless when the PT proxy (a
complicate debugging instrumentation for TT mode) is not enabled.  In fact, it
only calls update_debugregs, which checks debugregs_seq against seq (to check
if the registers are up-to-date - seq here means a "version number" of the

If the ptrace proxy is not enabled, debugregs_seq always stays 0 and
update_debugregs will be a no-op.  So, optimize this out (the compiler can't
do it).

Also, I've been disappointed by the fact that it would make a lot of sense if,
after calling a successful
current->thread.arch.debugregs_seq were updated with the new debugregs_seq.
But this is not done.  Is this a bug or a feature?  For all purposes, it seems
a bug (otherwise the whole mechanism does not make sense, which is also a
possibility to check), which causes some performance only problems (not
correctness), since we write_debugregs when not needed.

Also, as suggested by Jeff, remove a redundant enabling of SIGVTALRM,
comprised in the subsequent local_irq_enable().  I'm just a bit dubious if
ordering matters there...
Signed-off-by: default avatarPaolo 'Blaisorblade' Giarrusso <>
Acked-by: default avatarJeff Dike <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent fbdf2161
......@@ -116,7 +116,11 @@ extern void *get_current(void);
extern struct task_struct *get_task(int pid, int require);
extern void machine_halt(void);
extern int is_syscall(unsigned long addr);
extern void arch_switch(void);
extern void arch_switch_to_tt(struct task_struct *from, struct task_struct *to);
extern void arch_switch_to_skas(struct task_struct *from, struct task_struct *to);
extern void free_irq(unsigned int, void *);
extern int cpu(void);
......@@ -14,7 +14,12 @@
#define MAX_REG_NR (UM_FRAME_SIZE / sizeof(unsigned long))
extern void update_debugregs(int seq);
static inline void update_debugregs(int seq) {}
/* syscall emulation path in ptrace */
......@@ -35,6 +35,8 @@ void switch_to_skas(void *prev, void *next)
arch_switch_to_skas(current->thread.prev_sched, current);
if(current->pid == 0)
......@@ -51,6 +51,13 @@ void switch_to_tt(void *prev, void *next)
c = 0;
/* Notice that here we "up" the semaphore on which "to" is waiting, and
* below (the read) we wait on this semaphore (which is implemented by
* switch_pipe) and go sleeping. Thus, after that, we have resumed in
* "to", and can't use any more the value of "from" (which is outdated),
* nor the value in "to" (since it was the task which stole us the CPU,
* which we don't care about). */
err = os_write_file(to->[1], &c, sizeof(c));
if(err != sizeof(c))
panic("write of switch_pipe failed, err = %d", -err);
......@@ -77,7 +84,7 @@ void switch_to_tt(void *prev, void *next)
change_sig(SIGALRM, alrm);
change_sig(SIGPROF, prof);
arch_switch_to_tt(prev_sched, current);
......@@ -141,7 +148,6 @@ static void new_thread_handler(int sig)
set_cmdline("(kernel thread)");
change_sig(SIGUSR1, 1);
change_sig(SIGVTALRM, 1);
change_sig(SIGPROF, 1);
if(!run_kernel_thread(fn, arg, &current->thread.exec_buf))
......@@ -15,9 +15,13 @@
#include "sysdep/sigcontext.h"
#include "sysdep/sc.h"
void arch_switch(void)
void arch_switch_to_tt(struct task_struct *from, struct task_struct *to)
void arch_switch_to_skas(struct task_struct *from, struct task_struct *to)
int is_syscall(unsigned long addr)
......@@ -14,6 +14,7 @@
#include "sysdep/thread.h"
#include "user.h"
#include "os.h"
#include "uml-config.h"
int ptrace_getregs(long pid, unsigned long *regs_out)
......@@ -43,6 +44,7 @@ int ptrace_setfpregs(long pid, unsigned long *regs)
return 0;
/* All the below stuff is of interest for TT mode only */
static void write_debugregs(int pid, unsigned long *regs)
struct user *dummy;
......@@ -75,7 +77,6 @@ static void read_debugregs(int pid, unsigned long *regs)
/* Accessed only by the tracing thread */
static unsigned long kernel_debugregs[8] = { [ 0 ... 7 ] = 0 };
static int debugregs_seq = 0;
void arch_enter_kernel(void *task, int pid)
......@@ -89,6 +90,11 @@ void arch_leave_kernel(void *task, int pid)
write_debugregs(pid, TASK_DEBUGREGS(task));
/* Accessed only by the tracing thread */
static int debugregs_seq;
/* Only called by the ptrace proxy */
void ptrace_pokeuser(unsigned long addr, unsigned long data)
if((addr < offsetof(struct user, u_debugreg[0])) ||
......@@ -109,6 +115,7 @@ static void update_debugregs_cb(void *arg)
write_debugregs(pid, kernel_debugregs);
/* Optimized out in its header when not defined */
void update_debugregs(int seq)
int me;
......@@ -118,6 +125,7 @@ void update_debugregs(int seq)
me = os_getpid();
initial_thread_cb(update_debugregs_cb, &me);
* Overrides for Emacs so that we follow Linus's tabbing style.
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