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Commit 972410b0 authored by Paolo 'Blaisorblade' Giarrusso's avatar Paolo 'Blaisorblade' Giarrusso Committed by Linus Torvalds
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[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
registers).

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
update_debugregs(current->thread.arch.debugregs_seq),
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 <blaisorblade@yahoo.it>
Acked-by: default avatarJeff Dike <jdike@addtoit.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent fbdf2161

arch/um/include/kern_util.h

+5 −1
Original line number Diff line number Diff line
@@ -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);

arch/um/include/sysdep-i386/ptrace.h

+5 −0
Original line number Diff line number Diff line
@@ -14,7 +14,12 @@ 
#define MAX_REG_NR (UM_FRAME_SIZE / sizeof(unsigned long))

#define MAX_REG_OFFSET (UM_FRAME_SIZE)



#ifdef UML_CONFIG_PT_PROXY

extern void update_debugregs(int seq);

#else

static inline void update_debugregs(int seq) {}

#endif





/* syscall emulation path in ptrace */

arch/um/kernel/skas/process_kern.c

+2 −0
Original line number Diff line number Diff line
@@ -35,6 +35,8 @@ void switch_to_skas(void *prev, void *next) 
	switch_threads(&from->thread.mode.skas.switch_buf,

		       to->thread.mode.skas.switch_buf);



	arch_switch_to_skas(current->thread.prev_sched, current);



	if(current->pid == 0)

		switch_timers(1);

}

arch/um/kernel/tt/process_kern.c

+8 −2
Original line number Diff line number Diff line
@@ -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->thread.mode.tt.switch_pipe[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();

	arch_switch_to_tt(prev_sched, current);



	flush_tlb_all();

	local_irq_restore(flags);
@@ -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);

	local_irq_enable();

	if(!run_kernel_thread(fn, arg, &current->thread.exec_buf))

arch/um/sys-i386/ptrace.c

+6 −2
Original line number Diff line number Diff line
@@ -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)

{

	update_debugregs(to->thread.arch.debugregs_seq);

}



void arch_switch_to_skas(struct task_struct *from, struct task_struct *to)

{

	update_debugregs(current->thread.arch.debugregs_seq);

}



int is_syscall(unsigned long addr)