Messages in this thread Patch in this message | | | Subject | [patch 3/4] uml: clean and extend arch_switch() usage | From | blaisorblade@yahoo ... | Date | Fri, 27 May 2005 02:40:21 +0200 |
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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(); _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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