From: blaisorblade@yahoo.it
To: jdike@addtoit.com
Cc: linux-kernel@vger.kernel.org,
user-mode-linux-devel@lists.sourceforge.net,
blaisorblade@yahoo.it
Subject: [patch 3/4] uml: clean and extend arch_switch() usage
Date: Fri, 27 May 2005 02:40:21 +0200 [thread overview]
Message-ID: <20050527004021.8188B1AEE98@zion.home.lan> (raw)
Call arch_switch also in switch_to_skas, even if it's a no-op for that case
(and mark this in the comment).
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.
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
---
linux-2.6.git-paolo/arch/um/include/kern_util.h | 5 ++++-
linux-2.6.git-paolo/arch/um/include/sysdep-i386/ptrace.h | 5 +++++
linux-2.6.git-paolo/arch/um/kernel/skas/process_kern.c | 4 +++-
linux-2.6.git-paolo/arch/um/kernel/tt/process_kern.c | 13 +++++++++++--
linux-2.6.git-paolo/arch/um/sys-i386/ptrace.c | 4 ++--
linux-2.6.git-paolo/arch/um/sys-i386/ptrace_user.c | 10 +++++++++-
6 files changed, 34 insertions(+), 7 deletions(-)
diff -puN arch/um/include/sysdep-i386/ptrace.h~uml-clean-arch_switch arch/um/include/sysdep-i386/ptrace.h
--- linux-2.6.git/arch/um/include/sysdep-i386/ptrace.h~uml-clean-arch_switch 2005-05-25 01:26:20.000000000 +0200
+++ linux-2.6.git-paolo/arch/um/include/sysdep-i386/ptrace.h 2005-05-25 01:26:20.000000000 +0200
@@ -12,7 +12,12 @@
#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 */
diff -puN arch/um/kernel/skas/process_kern.c~uml-clean-arch_switch arch/um/kernel/skas/process_kern.c
--- linux-2.6.git/arch/um/kernel/skas/process_kern.c~uml-clean-arch_switch 2005-05-25 01:26:20.000000000 +0200
+++ linux-2.6.git-paolo/arch/um/kernel/skas/process_kern.c 2005-05-25 01:26:20.000000000 +0200
@@ -41,10 +41,12 @@ void *switch_to_skas(void *prev, void *n
switch_threads(&from->thread.mode.skas.switch_buf,
to->thread.mode.skas.switch_buf);
+ arch_switch(current->thread.prev_sched, current);
+
if(current->pid == 0)
switch_timers(1);
- return(current->thread.prev_sched);
+ return current->thread.prev_sched;
}
extern void schedule_tail(struct task_struct *prev);
diff -puN arch/um/sys-i386/ptrace.c~uml-clean-arch_switch arch/um/sys-i386/ptrace.c
--- linux-2.6.git/arch/um/sys-i386/ptrace.c~uml-clean-arch_switch 2005-05-25 01:26:20.000000000 +0200
+++ linux-2.6.git-paolo/arch/um/sys-i386/ptrace.c 2005-05-25 01:26:20.000000000 +0200
@@ -14,9 +14,9 @@
#include "sysdep/sigcontext.h"
#include "sysdep/sc.h"
-void arch_switch(void)
+void arch_switch(struct task_struct *from, struct task_struct *to)
{
- update_debugregs(current->thread.arch.debugregs_seq);
+ CHOOSE_MODE(update_debugregs(to->thread.arch.debugregs_seq), 0);
}
int is_syscall(unsigned long addr)
diff -puN arch/um/sys-i386/ptrace_user.c~uml-clean-arch_switch arch/um/sys-i386/ptrace_user.c
--- linux-2.6.git/arch/um/sys-i386/ptrace_user.c~uml-clean-arch_switch 2005-05-25 01:26:20.000000000 +0200
+++ linux-2.6.git-paolo/arch/um/sys-i386/ptrace_user.c 2005-05-25 01:26:20.000000000 +0200
@@ -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
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, unsi
/* 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 p
write_debugregs(pid, TASK_DEBUGREGS(task));
}
+#ifdef UML_CONFIG_PT_PROXY
+/* Accessed only by the tracing thread */
+static int debugregs_seq = 0;
+
+/* 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 *ar
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);
}
+#endif
/*
* Overrides for Emacs so that we follow Linus's tabbing style.
diff -puN arch/um/include/kern_util.h~uml-clean-arch_switch arch/um/include/kern_util.h
--- linux-2.6.git/arch/um/include/kern_util.h~uml-clean-arch_switch 2005-05-25 01:26:20.000000000 +0200
+++ linux-2.6.git-paolo/arch/um/include/kern_util.h 2005-05-25 01:26:20.000000000 +0200
@@ -107,7 +107,10 @@ 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);
+
+struct task_struct;
+extern void arch_switch(struct task_struct *from, struct task_struct *to);
+
extern void free_irq(unsigned int, void *);
extern int um_in_interrupt(void);
extern int cpu(void);
diff -puN arch/um/kernel/tt/process_kern.c~uml-clean-arch_switch arch/um/kernel/tt/process_kern.c
--- linux-2.6.git/arch/um/kernel/tt/process_kern.c~uml-clean-arch_switch 2005-05-25 01:26:20.000000000 +0200
+++ linux-2.6.git-paolo/arch/um/kernel/tt/process_kern.c 2005-05-25 01:27:00.000000000 +0200
@@ -55,6 +55,13 @@ void *switch_to_tt(void *prev, void *nex
c = 0;
set_current(to);
+ /* 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);
@@ -81,12 +88,12 @@ void *switch_to_tt(void *prev, void *nex
change_sig(SIGALRM, alrm);
change_sig(SIGPROF, prof);
- arch_switch();
+ arch_switch(prev_sched, current);
flush_tlb_all();
local_irq_restore(flags);
- return(current->thread.prev_sched);
+ return prev_sched;
}
void release_thread_tt(struct task_struct *task)
@@ -147,6 +154,8 @@ static void new_thread_handler(int sig)
set_cmdline("(kernel thread)");
change_sig(SIGUSR1, 1);
+ /* XXX: This is bogus, it's already done in local_irq_enable. Or does
+ * ordering matters? */
change_sig(SIGVTALRM, 1);
change_sig(SIGPROF, 1);
local_irq_enable();
_
reply other threads:[~2005-05-27 1:14 UTC|newest]
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