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Message-ID: <517f3f820807020404u7dbe6dc9n7754209200827a97@mail.gmail.com>
Date: Wed, 2 Jul 2008 13:04:52 +0200
From: "Michael Kerrisk" <mtk.manpages@gmail.com>
To: "eranian@googlemail.com" <eranian@googlemail.com>
Subject: Re: [patch 17/19] perfmon2 minimal v3: system calls
Cc: linux-kernel@vger.kernel.org
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On 6/30/08, eranian@googlemail.com <eranian@googlemail.com> wrote:
> This patch adds the top level perfmon2 system calls.
>
>  Signed-off-by: Stephane Eranian <eranian@gmail.com>

Stephane,

Is their some documentation for these new system calls?

Cheers,

Michael

===================================================================
>  --- /dev/null   1970-01-01 00:00:00.000000000 +0000
>  +++ linux-next/perfmon/perfmon_syscalls.c       2008-06-30 13:48:28.000000000 +0200
>  @@ -0,0 +1,719 @@
>  +/*
>  + * perfmon_syscalls.c: perfmon2 system call interface
>  + *
>  + * This file implements the perfmon2 interface which
>  + * provides access to the hardware performance counters
>  + * of the host processor.
>  + *
>  + * The initial version of perfmon.c was written by
>  + * Ganesh Venkitachalam, IBM Corp.
>  + *
>  + * Then it was modified for perfmon-1.x by Stephane Eranian and
>  + * David Mosberger, Hewlett Packard Co.
>  + *
>  + * Version Perfmon-2.x is a complete rewrite of perfmon-1.x
>  + * by Stephane Eranian, Hewlett Packard Co.
>  + *
>  + * Copyright (c) 1999-2006 Hewlett-Packard Development Company, L.P.
>  + * Contributed by Stephane Eranian <eranian@hpl.hp.com>
>  + *                David Mosberger-Tang <davidm@hpl.hp.com>
>  + *
>  + * More information about perfmon available at:
>  + *     http://perfmon2.sf.net
>  + *
>  + * This program is free software; you can redistribute it and/or
>  + * modify it under the terms of version 2 of the GNU General Public
>  + * License as published by the Free Software Foundation.
>  + *
>  + * This program is distributed in the hope that it will be useful,
>  + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>  + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>  + * General Public License for more details.
>  + *
>  + * You should have received a copy of the GNU General Public License
>  + * along with this program; if not, write to the Free Software
>  + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
>  + * 02111-1307 USA
>  + */
>  +#include <linux/kernel.h>
>  +#include <linux/fs.h>
>  +#include <linux/ptrace.h>
>  +#include <linux/perfmon_kern.h>
>  +#include <linux/uaccess.h>
>  +#include "perfmon_priv.h"
>  +
>  +/*
>  + * Context locking rules:
>  + * ---------------------
>  + *     - any thread with access to the file descriptor of a context can
>  + *       potentially issue perfmon calls
>  + *
>  + *     - calls must be serialized to guarantee correctness
>  + *
>  + *     - as soon as a context is attached to a thread or CPU, it may be
>  + *       actively monitoring. On some architectures, such as IA-64, this
>  + *       is true even though the pfm_start() call has not been made. This
>  + *       comes from the fact that on some architectures, it is possible to
>  + *       start/stop monitoring from userland.
>  + *
>  + *     - If monitoring is active, then there can PMU interrupts. Because
>  + *       context accesses must be serialized, the perfmon system calls
>  + *       must mask interrupts as soon as the context is attached.
>  + *
>  + *     - perfmon system calls that operate with the context unloaded cannot
>  + *       assume it is actually unloaded when they are called. They first need
>  + *       to check and for that they need interrupts masked. Then, if the
>  + *       context is actually unloaded, they can unmask interrupts.
>  + *
>  + *     - interrupt masking holds true for other internal perfmon functions as
>  + *       well. Except for PMU interrupt handler because those interrupts
>  + *       cannot be nested.
>  + *
>  + *     - we mask ALL interrupts instead of just the PMU interrupt because we
>  + *       also need to protect against timer interrupts which could trigger
>  + *       a set switch.
>  + */
>  +
>  +/*
>  + * upper limit for count in calls that take vector arguments. This is used
>  + * to prevent for multiplication overflow when we compute actual storage size
>  + */
>  +#define PFM_MAX_ARG_COUNT(m) (INT_MAX/sizeof(*(m)))
>  +
>  +struct pfm_syscall_cookie {
>  +       struct file *filp;
>  +       int fput_needed;
>  +};
>  +
>  +/*
>  + * cannot attach if :
>  + *     - kernel task
>  + *     - task not owned by caller (checked by ptrace_may_attach())
>  + *     - task is dead or zombie
>  + *     - cannot use blocking notification when self-monitoring
>  + */
>  +static int pfm_task_incompatible(struct pfm_context *ctx,
>  +                                struct task_struct *task)
>  +{
>  +       /*
>  +        * cannot attach to a kernel thread
>  +        */
>  +       if (!task->mm) {
>  +               PFM_DBG("cannot attach to kernel thread [%d]", task->pid);
>  +               return -EPERM;
>  +       }
>  +
>  +       /*
>  +        * cannot attach to a zombie task
>  +        */
>  +       if (task->exit_state == EXIT_ZOMBIE || task->exit_state == EXIT_DEAD) {
>  +               PFM_DBG("cannot attach to zombie/dead task [%d]", task->pid);
>  +               return -EBUSY;
>  +       }
>  +       return 0;
>  +}
>  +
>  +/**
>  + * pfm_get_task -- check permission and acquire task to monitor
>  + * @ctx: perfmon context
>  + * @pid: identification of the task to check
>  + * @task: upon return, a pointer to the task to monitor
>  + *
>  + * This function  is used in per-thread mode only AND when not
>  + * self-monitoring. It finds the task to monitor and checks
>  + * that the caller has permissions to attach. It also checks
>  + * that the task is stopped via ptrace so that we can safely
>  + * modify its state.
>  + *
>  + * task refcount is incremented when succesful.
>  + */
>  +static int pfm_get_task(struct pfm_context *ctx, pid_t pid,
>  +                       struct task_struct **task)
>  +{
>  +       struct task_struct *p;
>  +       int ret = 0, ret1 = 0;
>  +
>  +       /*
>  +        * When attaching to another thread we must ensure
>  +        * that the thread is actually stopped. Just like with
>  +        * perfmon system calls, we enforce that the thread
>  +        * be ptraced and STOPPED by using ptrace_check_attach().
>  +        *
>  +        * As a consequence, only the ptracing parent can actually
>  +        * attach a context to a thread. Obviously, this constraint
>  +        * does not exist for self-monitoring threads.
>  +        *
>  +        * We use ptrace_may_attach() to check for permission.
>  +        */
>  +       read_lock(&tasklist_lock);
>  +
>  +       p = find_task_by_pid(pid);
>  +       if (p)
>  +               get_task_struct(p);
>  +
>  +       read_unlock(&tasklist_lock);
>  +
>  +       if (!p) {
>  +               PFM_DBG("task not found %d", pid);
>  +               return -ESRCH;
>  +       }
>  +
>  +       ret = -EPERM;
>  +
>  +       /*
>  +        * returns 0 if cannot attach
>  +        */
>  +       ret1 = ptrace_may_access(p, PTRACE_MODE_ATTACH);
>  +       if (ret1)
>  +               ret = ptrace_check_attach(p, 0);
>  +
>  +       PFM_DBG("may_attach=%d check_attach=%d", ret1, ret);
>  +
>  +       if (ret || !ret1)
>  +               goto error;
>  +
>  +       ret = pfm_task_incompatible(ctx, p);
>  +       if (ret)
>  +               goto error;
>  +
>  +       *task = p;
>  +
>  +       return 0;
>  +error:
>  +       if (!(ret1 || ret))
>  +               ret = -EPERM;
>  +
>  +       put_task_struct(p);
>  +
>  +       return ret;
>  +}
>  +
>  +/*
>  + * context must be locked when calling this function
>  + */
>  +int __pfm_check_task_state(struct pfm_context *ctx, int check_mask,
>  +                        unsigned long *flags)
>  +{
>  +       struct task_struct *task;
>  +       unsigned long local_flags, new_flags;
>  +       int state, ret;
>  +
>  +recheck:
>  +       /*
>  +        * task is NULL for system-wide context
>  +        */
>  +       task = ctx->task;
>  +       state = ctx->state;
>  +       local_flags = *flags;
>  +
>  +       PFM_DBG("state=%d check_mask=0x%x task=[%d]",
>  +               state, check_mask, task ? task->pid:-1);
>  +       /*
>  +        * if the context is detached, then we do not touch
>  +        * hardware, therefore there is not restriction on when we can
>  +        * access it.
>  +        */
>  +       if (state == PFM_CTX_UNLOADED)
>  +               return 0;
>  +       /*
>  +        * no command can operate on a zombie context.
>  +        * A context becomes zombie when the file that identifies
>  +        * it is closed while the context is still attached to the
>  +        * thread it monitors.
>  +        */
>  +       if (state == PFM_CTX_ZOMBIE)
>  +               return -EINVAL;
>  +
>  +       /*
>  +        * at this point, state is PFM_CTX_LOADED
>  +        */
>  +
>  +       /*
>  +        * some commands require the context to be unloaded to operate
>  +        */
>  +       if (check_mask & PFM_CMD_UNLOADED)  {
>  +               PFM_DBG("state=%d, cmd needs context unloaded", state);
>  +               return -EBUSY;
>  +       }
>  +
>  +       /*
>  +        * self-monitoring always ok.
>  +        */
>  +       if (task == current)
>  +               return 0;
>  +
>  +       /*
>  +        * at this point, monitoring another thread
>  +        */
>  +
>  +       /*
>  +        * When we operate on another thread, we must wait for it to be
>  +        * stopped and completely off any CPU as we need to access the
>  +        * PMU state (or machine state).
>  +        *
>  +        * A thread can be put in the STOPPED state in various ways
>  +        * including PTRACE_ATTACH, or when it receives a SIGSTOP signal.
>  +        * We enforce that the thread must be ptraced, so it is stopped
>  +        * AND it CANNOT wake up while we operate on it because this
>  +        * would require an action from the ptracing parent which is the
>  +        * thread that is calling this function.
>  +        *
>  +        * The dependency on ptrace, imposes that only the ptracing
>  +        * parent can issue command on a thread. This is unfortunate
>  +        * but we do not know of a better way of doing this.
>  +        */
>  +       if (check_mask & PFM_CMD_STOPPED) {
>  +
>  +               spin_unlock_irqrestore(&ctx->lock, local_flags);
>  +
>  +               /*
>  +                * check that the thread is ptraced AND STOPPED
>  +                */
>  +               ret = ptrace_check_attach(task, 0);
>  +
>  +               spin_lock_irqsave(&ctx->lock, new_flags);
>  +
>  +               /*
>  +                * flags may be different than when we released the lock
>  +                */
>  +               *flags = new_flags;
>  +
>  +               if (ret)
>  +                       return ret;
>  +               /*
>  +                * we must recheck to verify if state has changed
>  +                */
>  +               if (unlikely(ctx->state != state)) {
>  +                       PFM_DBG("old_state=%d new_state=%d",
>  +                               state,
>  +                               ctx->state);
>  +                       goto recheck;
>  +               }
>  +       }
>  +       return 0;
>  +}
>  +
>  +int pfm_check_task_state(struct pfm_context *ctx, int check_mask,
>  +                        unsigned long *flags)
>  +{
>  +       int ret;
>  +       ret  = __pfm_check_task_state(ctx, check_mask, flags);
>  +       PFM_DBG("ret=%d",ret);
>  +       return ret;
>  +}
>  +
>  +/*
>  + * pfm_get_args - Function used to copy the syscall argument into kernel memory
>  + * @ureq: user argument
>  + * @sz: user argument size
>  + * @lsz: size of stack buffer
>  + * @laddr: stack buffer address
>  + * @req: point to start of kernel copy of the argument
>  + * @ptr_free: address of kernel copy to free
>  + *
>  + * There are two options:
>  + *     - use a stack buffer described by laddr (addresses) and lsz (size)
>  + *     - allocate memory
>  + *
>  + * return:
>  + *     < 0 : in case of error (ptr_free may not be updated)
>  + *       0 : success
>  + *      - req: points to base of kernel copy of arguments
>  + *     - ptr_free: address of buffer to free by caller on exit.
>  + *                 NULL if using the stack buffer
>  + *
>  + * when ptr_free is not NULL upon return, the caller must kfree()
>  + */
>  +int pfm_get_args(void __user *ureq, size_t sz, size_t lsz, void *laddr,
>  +                void **req, void **ptr_free)
>  +{
>  +       void *addr;
>  +
>  +       /*
>  +        * check syadmin argument limit
>  +        */
>  +       if (unlikely(sz > pfm_controls.arg_mem_max)) {
>  +               PFM_DBG("argument too big %zu max=%zu",
>  +                       sz,
>  +                       pfm_controls.arg_mem_max);
>  +               return -E2BIG;
>  +       }
>  +
>  +       /*
>  +        * check if vector fits on stack buffer
>  +        */
>  +       if (sz > lsz) {
>  +               addr = kmalloc(sz, GFP_KERNEL);
>  +               if (unlikely(addr == NULL))
>  +                       return -ENOMEM;
>  +               *ptr_free = addr;
>  +       } else {
>  +               addr = laddr;
>  +               *req = laddr;
>  +               *ptr_free = NULL;
>  +       }
>  +
>  +       /*
>  +        * bring the data in
>  +        */
>  +       if (unlikely(copy_from_user(addr, ureq, sz))) {
>  +               if (addr != laddr)
>  +                       kfree(addr);
>  +               return -EFAULT;
>  +       }
>  +
>  +       /*
>  +        * base address of kernel buffer
>  +        */
>  +       *req = addr;
>  +
>  +       return 0;
>  +}
>  +
>  +/**
>  + * pfm_acquire_ctx_from_fd -- get ctx from file descriptor
>  + * @fd: file descriptor
>  + * @ctx: pointer to pointer of context updated on return
>  + * @cookie: opaque structure to use for release
>  + *
>  + * This helper function extracts the ctx from the file descriptor.
>  + * It also increments the refcount of the file structure. Thus
>  + * it updates the cookie so the refcount can be decreased when
>  + * leaving the perfmon syscall via pfm_release_ctx_from_fd
>  + */
>  +static int pfm_acquire_ctx_from_fd(int fd, struct pfm_context **ctx,
>  +                                  struct pfm_syscall_cookie *cookie)
>  +{
>  +       struct file *filp;
>  +       int fput_needed;
>  +
>  +       filp = fget_light(fd, &fput_needed);
>  +       if (unlikely(filp == NULL)) {
>  +               PFM_DBG("invalid fd %d", fd);
>  +               return -EBADF;
>  +       }
>  +
>  +       *ctx = filp->private_data;
>  +
>  +       if (unlikely(!*ctx || filp->f_op != &pfm_file_ops)) {
>  +               PFM_DBG("fd %d not related to perfmon", fd);
>  +               return -EBADF;
>  +       }
>  +       cookie->filp = filp;
>  +       cookie->fput_needed = fput_needed;
>  +
>  +       return 0;
>  +}
>  +
>  +/**
>  + * pfm_release_ctx_from_fd -- decrease refcount of file associated with context
>  + * @cookie: the cookie structure initialized by pfm_acquire_ctx_from_fd
>  + */
>  +static inline void pfm_release_ctx_from_fd(struct pfm_syscall_cookie *cookie)
>  +{
>  +       fput_light(cookie->filp, cookie->fput_needed);
>  +}
>  +
>  +/*
>  + * unlike the other perfmon system calls, this one returns a file descriptor
>  + * or a value < 0 in case of error, very much like open() or socket()
>  + */
>  +asmlinkage long sys_pfm_create_context(struct pfarg_ctx __user *ureq,
>  +                                      char __user *fmt_name,
>  +                                      void __user *fmt_uarg, size_t fmt_size)
>  +{
>  +       struct pfarg_ctx req;
>  +
>  +       PFM_DBG("req=%p fmt=%p fmt_arg=%p size=%zu",
>  +               ureq, fmt_name, fmt_uarg, fmt_size);
>  +
>  +       if (perfmon_disabled)
>  +               return -ENOSYS;
>  +
>  +       if (copy_from_user(&req, ureq, sizeof(req)))
>  +               return -EFAULT;
>  +
>  +       if (fmt_name || fmt_uarg || fmt_size)
>  +               return -EINVAL;
>  +
>  +       return __pfm_create_context(req.ctx_flags);
>  +}
>  +
>  +asmlinkage long sys_pfm_write_pmcs(int fd, struct pfarg_pmc __user *ureq,
>  +                                  int count)
>  +{
>  +       struct pfm_context *ctx;
>  +       struct pfm_syscall_cookie cookie;
>  +       struct pfarg_pmc pmcs[PFM_PMC_STK_ARG];
>  +       struct pfarg_pmc *req;
>  +       void *fptr;
>  +       unsigned long flags;
>  +       size_t sz;
>  +       int ret;
>  +
>  +       PFM_DBG("fd=%d req=%p count=%d", fd, ureq, count);
>  +
>  +       if (count < 0 || count >= PFM_MAX_ARG_COUNT(ureq)) {
>  +               PFM_DBG("invalid arg count %d", count);
>  +               return -EINVAL;
>  +       }
>  +
>  +       sz = count*sizeof(*ureq);
>  +
>  +       ret = pfm_acquire_ctx_from_fd(fd, &ctx, &cookie);
>  +       if (ret)
>  +               return ret;
>  +
>  +       ret = pfm_get_args(ureq, sz, sizeof(pmcs), pmcs, (void **)&req, &fptr);
>  +       if (ret)
>  +               goto error;
>  +
>  +       spin_lock_irqsave(&ctx->lock, flags);
>  +
>  +       ret = pfm_check_task_state(ctx, PFM_CMD_STOPPED, &flags);
>  +       if (!ret)
>  +               ret = __pfm_write_pmcs(ctx, req, count);
>  +
>  +       spin_unlock_irqrestore(&ctx->lock, flags);
>  +
>  +       /*
>  +        * This function may be on the critical path.
>  +        * We want to avoid the branch if unecessary.
>  +        */
>  +       if (fptr)
>  +               kfree(fptr);
>  +error:
>  +       pfm_release_ctx_from_fd(&cookie);
>  +       return ret;
>  +}
>  +
>  +asmlinkage long sys_pfm_write_pmds(int fd, struct pfarg_pmd __user *ureq,
>  +                                  int count)
>  +{
>  +       struct pfm_context *ctx;
>  +       struct pfm_syscall_cookie cookie;
>  +       struct pfarg_pmd pmds[PFM_PMD_STK_ARG];
>  +       struct pfarg_pmd *req;
>  +       void *fptr;
>  +       unsigned long flags;
>  +       size_t sz;
>  +       int ret;
>  +
>  +       PFM_DBG("fd=%d req=%p count=%d", fd, ureq, count);
>  +
>  +       if (count < 0 || count >= PFM_MAX_ARG_COUNT(ureq)) {
>  +               PFM_DBG("invalid arg count %d", count);
>  +               return -EINVAL;
>  +       }
>  +
>  +       sz = count*sizeof(*ureq);
>  +
>  +       ret = pfm_acquire_ctx_from_fd(fd, &ctx, &cookie);
>  +       if (ret)
>  +               return ret;
>  +
>  +       ret = pfm_get_args(ureq, sz, sizeof(pmds), pmds, (void **)&req, &fptr);
>  +       if (ret)
>  +               goto error;
>  +
>  +       spin_lock_irqsave(&ctx->lock, flags);
>  +
>  +       ret = pfm_check_task_state(ctx, PFM_CMD_STOPPED, &flags);
>  +       if (!ret)
>  +               ret = __pfm_write_pmds(ctx, req, count);
>  +
>  +       spin_unlock_irqrestore(&ctx->lock, flags);
>  +
>  +       if (fptr)
>  +               kfree(fptr);
>  +error:
>  +       pfm_release_ctx_from_fd(&cookie);
>  +       return ret;
>  +}
>  +
>  +asmlinkage long sys_pfm_read_pmds(int fd, struct pfarg_pmd __user *ureq,
>  +                                 int count)
>  +{
>  +       struct pfm_context *ctx;
>  +       struct pfm_syscall_cookie cookie;
>  +       struct pfarg_pmd pmds[PFM_PMD_STK_ARG];
>  +       struct pfarg_pmd *req;
>  +       void *fptr;
>  +       unsigned long flags;
>  +       size_t sz;
>  +       int ret;
>  +
>  +       PFM_DBG("fd=%d req=%p count=%d", fd, ureq, count);
>  +
>  +       if (count < 0 || count >= PFM_MAX_ARG_COUNT(ureq))
>  +               return -EINVAL;
>  +
>  +       sz = count*sizeof(*ureq);
>  +
>  +       ret = pfm_acquire_ctx_from_fd(fd, &ctx, &cookie);
>  +       if (ret)
>  +               return ret;
>  +
>  +       ret = pfm_get_args(ureq, sz, sizeof(pmds), pmds, (void **)&req, &fptr);
>  +       if (ret)
>  +               goto error;
>  +
>  +       spin_lock_irqsave(&ctx->lock, flags);
>  +
>  +       ret = pfm_check_task_state(ctx, PFM_CMD_STOPPED, &flags);
>  +       if (!ret)
>  +               ret = __pfm_read_pmds(ctx, req, count);
>  +
>  +       spin_unlock_irqrestore(&ctx->lock, flags);
>  +
>  +       if (copy_to_user(ureq, req, sz))
>  +               ret = -EFAULT;
>  +
>  +       if (fptr)
>  +               kfree(fptr);
>  +error:
>  +       pfm_release_ctx_from_fd(&cookie);
>  +       return ret;
>  +}
>  +
>  +asmlinkage long sys_pfm_stop(int fd)
>  +{
>  +       struct pfm_context *ctx;
>  +       struct pfm_syscall_cookie cookie;
>  +       unsigned long flags;
>  +       int ret;
>  +
>  +       PFM_DBG("fd=%d", fd);
>  +
>  +       ret = pfm_acquire_ctx_from_fd(fd, &ctx, &cookie);
>  +       if (ret)
>  +               return ret;
>  +
>  +       spin_lock_irqsave(&ctx->lock, flags);
>  +
>  +       ret = pfm_check_task_state(ctx, PFM_CMD_STOPPED, &flags);
>  +       if (!ret)
>  +               ret = __pfm_stop(ctx);
>  +
>  +       spin_unlock_irqrestore(&ctx->lock, flags);
>  +
>  +       pfm_release_ctx_from_fd(&cookie);
>  +       return ret;
>  +}
>  +
>  +asmlinkage long sys_pfm_start(int fd)
>  +{
>  +       struct pfm_context *ctx;
>  +       struct pfm_syscall_cookie cookie;
>  +       unsigned long flags;
>  +       int ret;
>  +
>  +       PFM_DBG("fd=%d", fd);
>  +
>  +       ret = pfm_acquire_ctx_from_fd(fd, &ctx, &cookie);
>  +       if (ret)
>  +               return ret;
>  +
>  +       spin_lock_irqsave(&ctx->lock, flags);
>  +
>  +       ret = pfm_check_task_state(ctx, PFM_CMD_STOPPED, &flags);
>  +       if (!ret)
>  +               ret = __pfm_start(ctx);
>  +
>  +       spin_unlock_irqrestore(&ctx->lock, flags);
>  +
>  +       pfm_release_ctx_from_fd(&cookie);
>  +       return ret;
>  +}
>  +
>  +asmlinkage long sys_pfm_load_context(int fd, struct pfarg_load __user *ureq)
>  +{
>  +       struct pfarg_load req;
>  +       struct pfm_context *ctx;
>  +       struct task_struct *task;
>  +       struct pfm_syscall_cookie cookie;
>  +       unsigned long flags;
>  +       int ret;
>  +
>  +       PFM_DBG("fd=%d ureq=%p", fd, ureq);
>  +
>  +       if (copy_from_user(&req, ureq, sizeof(req)))
>  +               return -EFAULT;
>  +
>  +       ret = pfm_acquire_ctx_from_fd(fd, &ctx, &cookie);
>  +       if (ret)
>  +               return ret;
>  +
>  +       task = current;
>  +
>  +       /*
>  +        * in per-thread mode (not self-monitoring), get a reference
>  +        * on task to monitor. This must be done with interrupts enabled
>  +        * Upon succesful return, refcount on task is increased.
>  +        *
>  +        * fget_light() is protecting the context.
>  +        */
>  +       if (req.load_pid != current->pid) {
>  +               ret = pfm_get_task(ctx, req.load_pid, &task);
>  +               if (ret)
>  +                       goto error;
>  +       }
>  +
>  +       /*
>  +        * irqsave is required to avoid race in case context is already
>  +        * loaded or with switch timeout in the case of self-monitoring
>  +        */
>  +       spin_lock_irqsave(&ctx->lock, flags);
>  +
>  +       ret = pfm_check_task_state(ctx, PFM_CMD_UNLOADED, &flags);
>  +       if (!ret)
>  +               ret = __pfm_load_context(ctx, task);
>  +
>  +       spin_unlock_irqrestore(&ctx->lock, flags);
>  +
>  +       /*
>  +        * in per-thread mode (not self-monitoring), we need
>  +        * to decrease refcount on task to monitor:
>  +        *   - load successful: we have a reference to the task in ctx->task
>  +        *   - load failed    : undo the effect of pfm_get_task()
>  +        */
>  +       if (task != current)
>  +               put_task_struct(task);
>  +error:
>  +       pfm_release_ctx_from_fd(&cookie);
>  +       return ret;
>  +}
>  +
>  +asmlinkage long sys_pfm_unload_context(int fd)
>  +{
>  +       struct pfm_context *ctx;
>  +       struct pfm_syscall_cookie cookie;
>  +       unsigned long flags;
>  +       int ret;
>  +
>  +       PFM_DBG("fd=%d", fd);
>  +
>  +       ret = pfm_acquire_ctx_from_fd(fd, &ctx, &cookie);
>  +       if (ret)
>  +               return ret;
>  +
>  +       spin_lock_irqsave(&ctx->lock, flags);
>  +
>  +       ret = pfm_check_task_state(ctx, PFM_CMD_STOPPED|PFM_CMD_UNLOAD,
>  +                                  &flags);
>  +       if (!ret)
>  +               ret = __pfm_unload_context(ctx);
>  +
>  +       spin_unlock_irqrestore(&ctx->lock, flags);
>  +
>  +       /*
>  +        * if unload was successful, then release the session
>  +        * must be called with interrupts enabled, thus we need
>  +        * to defer until are out of __pfm_unload_context()
>  +        */
>  +       if (!ret)
>  +               pfm_session_release();
>  +
>  +       pfm_release_ctx_from_fd(&cookie);
>  +       return ret;
>  +}
>  Index: linux-next/include/linux/perfmon.h
>  ===================================================================
>  --- linux-next.orig/include/linux/perfmon.h     2008-06-26 20:06:58.000000000 +0200
>  +++ linux-next/include/linux/perfmon.h  2008-06-30 13:48:29.000000000 +0200
>  @@ -46,6 +46,16 @@
>   #define PFM_PMC_BV     PFM_BVSIZE(PFM_MAX_PMCS)
>
>   /*
>  + * argument to pfm_create_context() system call
>  + * structure shared with user level
>  + */
>  +struct pfarg_ctx {
>  +       __u32           ctx_flags;        /* context flags */
>  +       __u32           ctx_reserved1;    /* for future use */
>  +       __u64           ctx_reserved2[7]; /* for future use */
>  +};
>  +
>  +/*
>   * argument to pfm_write_pmcs() system call.
>   * structure shared with user level
>   */
>  @@ -70,6 +80,17 @@
>   };
>
>   /*
>  + * argument to pfm_load_context() system call.
>  + * structure shared with user level
>  + */
>  +struct pfarg_load {
>  +       __u32   load_pid;          /* thread or CPU to attach to */
>  +       __u16   load_reserved0;    /* for future use */
>  +       __u16   load_reserved1;    /* for future use */
>  +       __u64   load_reserved2[3]; /* for future use */
>  +};
>  +
>  +/*
>   * default value for the user and group security parameters in
>   * /proc/sys/kernel/perfmon/sys_group
>   * /proc/sys/kernel/perfmon/task_group
>  Index: linux-next/kernel/sys_ni.c
>  ===================================================================
>  --- linux-next.orig/kernel/sys_ni.c     2008-06-26 17:46:28.000000000 +0200
>  +++ linux-next/kernel/sys_ni.c  2008-06-26 20:07:41.000000000 +0200
>  @@ -161,3 +161,13 @@
>   cond_syscall(compat_sys_timerfd_settime);
>   cond_syscall(compat_sys_timerfd_gettime);
>   cond_syscall(sys_eventfd);
>  +
>  +/* perfmon */
>  +cond_syscall(sys_pfm_create_context);
>  +cond_syscall(sys_pfm_write_pmcs);
>  +cond_syscall(sys_pfm_write_pmds);
>  +cond_syscall(sys_pfm_read_pmds);
>  +cond_syscall(sys_pfm_start);
>  +cond_syscall(sys_pfm_stop);
>  +cond_syscall(sys_pfm_load_context);
>  +cond_syscall(sys_pfm_unload_context);
>  Index: linux-next/perfmon/Makefile
>  ===================================================================
>  --- linux-next.orig/perfmon/Makefile    2008-06-26 20:07:01.000000000 +0200
>  +++ linux-next/perfmon/Makefile 2008-06-30 13:48:28.000000000 +0200
>  @@ -7,4 +7,5 @@
>         perfmon_init.o perfmon_ctxsw.o \
>         perfmon_intr.o perfmon_pmu.o \
>         perfmon_sysfs.o perfmon_rw.o \
>  -       perfmon_activate.o perfmon_attach.o
>  +       perfmon_activate.o perfmon_attach.o \
>  +       perfmon_syscalls.o
>
>  --
>
>
>  --
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>


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html
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