On Tue, 29 May 2007, Stephane Eranian wrote:
> --- linux-2.6.22.base/perfmon/perfmon_syscalls.c 1969-12-31 16:00:00.000000000 -0800
> +++ linux-2.6.22/perfmon/perfmon_syscalls.c 2007-05-29 03:24:14.000000000 -0700
> @@ -0,0 +1,991 @@
> +/*
> + * 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 <[email protected]>
> + * David Mosberger-Tang <[email protected]>
> + *
> + * 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/perfmon.h>
> +#include <linux/fs.h>
> +#include <linux/ptrace.h>
> +#include <asm/uaccess.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.
> + */
> +
> +/*
> + * cannot attach if :
> + * - kernel task
> + * - task not owned by caller
> + * - 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)
> +{
> + /*
> + * no kernel task or task not owned by caller
> + */
> + if (!task->mm) {
> + PFM_DBG("cannot attach to kernel thread [%d]", task->pid);
> + return -EPERM;
> + }
This isn't a sufficient check for whether a task is owned by the caller.
> +
> + /*
> + * cannot block in self-monitoring mode
> + */
> + if (ctx->flags.block && task == current) {
> + PFM_DBG("cannot load a in blocking mode on self for [%d]",
> + task->pid);
> + return -EINVAL;
> + }
Poor description of trying block notification on self.
> +
> + 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;
> +}
> +
> +/*
> + * 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 persmissions to attach. It also checks
> + * that the task is stopped via ptrace so that we can safely
> + * modify its state.
> + *
> + * task refcount is increment when succesful.
> + */
> +int pfm_get_task(struct pfm_context *ctx, pid_t pid, struct task_struct **task)
> +{
This function could be marked static even though it's exported through
perfmon.h in patch 13. It is unreferenced elsewhere.
Why can't this be done with just struct task_struct *task as the third
formal and change the assignment later to task = p?
> + 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.
> + * No permission checking is needed for self monitoring.
> + */
> + read_lock(&tasklist_lock);
> +
> + p = find_task_by_pid(pid);
> + if (p)
> + get_task_struct(p);
> +
> + read_unlock(&tasklist_lock);
> +
> + if (p == NULL)
> + return -ESRCH;
> +
> + ret = -EPERM;
> +
> + /*
> + * returns 0 if cannot attach
> + */
> + ret1 = ptrace_may_attach(p);
> + 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;
> +}
> +
> +int pfm_check_task_state(struct pfm_context *ctx, int check_mask,
> + unsigned long *flags)
> +{
Another function that can be static.
You need to mention the fact that ctx->lock needs to be locked before
calling this function.
No need to send a pointer to flags, just send the unsigned long value
itself, if necessary. All callers currently send the address of an
automatic anyway. Unlocking and then relocking ctx->lock by returning the
new flags is inappropriate.
> + 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", state, check_mask);
> + /*
> + * 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 or PFM_CTX_MASKED
> + */
> +
> + /*
> + * 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;
> +
> + /*
> + * for syswide, the calling thread must be running on the cpu
> + * the context is bound to. There cannot be preemption as we
> + * check with interrupts disabled.
> + */
> + if (ctx->flags.system) {
> + if (ctx->cpu != smp_processor_id())
> + return -EBUSY;
> + return 0;
> + }
> +
> + /*
> + * at this point, monitoring another thread
> + */
> +
> + /*
> + * the pfm_unload_context() command is allowed on masked context
> + */
> + if (state == PFM_CTX_MASKED && !(check_mask & PFM_CMD_UNLOAD))
> + return 0;
> +
> + /*
> + * 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 for 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;
You can't do this, you'll need to either separate these functions out by
having pfm_check_task_state() indicate by a return value that
ptrace_check_attach() should be checked or that we've already failed, or
come up with a non-locking solution.
> +
> + if (ret)
> + return ret;
> + /*
> + * we must recheck to verify if state has changed
> + */
> + if (ctx->state != state) {
> + PFM_DBG("old_state=%d new_state=%d",
> + state,
> + ctx->state);
> + goto recheck;
This should be unnecessary when you no longer drop the ctx->lock in this
function.
> + }
> + }
> + return 0;
> +}
> +
> +int pfm_get_args(void __user *ureq, size_t sz, size_t lsz, void *laddr,
> + void **req, void **ptr_free)
> +{
Another function that can be static.
Needs a comment to say that *req and *ptr_free get kmalloc'd and requires
a free() of at least one of them upon return.
> + void *addr;
> +
> + /*
> + * check if we can get by with stack buffer
> + */
> + if (sz <= lsz) {
> + *req = laddr;
> + *ptr_free = NULL;
> + return copy_from_user(laddr, ureq, sz) ? -EFAULT : 0;
> + }
> +
> + if (unlikely(sz > pfm_controls.arg_mem_max)) {
> + PFM_DBG("argument too big %zu max=%zu",
> + sz,
> + pfm_controls.arg_mem_max);
> + return -E2BIG;
> + }
> +
> + addr = kmalloc(sz, GFP_KERNEL);
> + if (unlikely(addr == NULL))
> + return -ENOMEM;
> +
> + if (copy_from_user(addr, ureq, sz)) {
> + kfree(addr);
> + return -EFAULT;
> + }
> + *req = *ptr_free = addr;
> +
> + return 0;
> +}
> +
> +int pfm_get_smpl_arg(char __user *fmt_uname, void __user *fmt_uarg, size_t usize, void **arg,
> + struct pfm_smpl_fmt **fmt)
> +{
Another function that can be static.
Needs a comment to say that *arg gets kmalloc'd and requires a free()
afterwards.
> + struct pfm_smpl_fmt *f;
> + char *fmt_name;
> + void *addr = NULL;
> + size_t sz;
> + int ret;
> +
> + fmt_name = getname(fmt_uname);
> + if (!fmt_name) {
> + PFM_DBG("getname failed");
> + return -ENOMEM;
> + }
> +
> + /*
> + * find fmt and increase refcount
> + */
> + f = pfm_smpl_fmt_get(fmt_name);
> +
> + putname(fmt_name);
> +
> + if (f == NULL) {
> + PFM_DBG("buffer format not found");
> + return -EINVAL;
> + }
> +
> + /*
> + * expected format argument size
> + */
> + sz = f->fmt_arg_size;
> +
> + /*
> + * check user size matches expected size
> + * usize = -1 is for IA-64 backward compatibility
> + */
> + ret = -EINVAL;
> + if (sz != usize && usize != -1) {
> + PFM_DBG("invalid arg size %zu, format expects %zu",
> + usize, sz);
> + goto error;
> + }
> +
> + if (sz) {
> + ret = -ENOMEM;
> + addr = kmalloc(sz, GFP_KERNEL);
> + if (addr == NULL)
> + goto error;
> +
> + ret = -EFAULT;
> + if (copy_from_user(addr, fmt_uarg, sz))
> + goto error;
> + }
> + *arg = addr;
> + *fmt = f;
> + return 0;
> +
> +error:
> + kfree(addr);
> + pfm_smpl_fmt_put(f);
> + return ret;
> +}
In the non-error case where we return 0, is pfm_smpl_fmt_put(f) taken care
of in pfm_context_free()?
> +
> +/*
> + * unlike the other perfmon system calls, this one return 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;
> + struct pfm_context *new_ctx;
> + struct pfm_smpl_fmt *fmt = NULL;
> + void *fmt_arg = NULL;
> + int ret;
> +
> + if (atomic_read(&perfmon_disabled))
> + return -ENOSYS;
Not really necessary for perfmon_disabled to be an atomic_t since it's
only set in pfm_init() and we would have returned 0 in that function when
we've initialized correctly. A simple unsigned char will work fine.
> +
> + if (copy_from_user(&req, ureq, sizeof(req)))
> + return -EFAULT;
> +
> + if (fmt_name) {
> + ret = pfm_get_smpl_arg(fmt_name, fmt_uarg, fmt_size, &fmt_arg, &fmt);
> + if (ret)
> + goto abort;
> + }
> +
> + ret = __pfm_create_context(&req, fmt, fmt_arg, PFM_NORMAL, &new_ctx);
> +
> + kfree(fmt_arg);
> +abort:
> + return ret;
> +}
> +
> +asmlinkage long sys_pfm_write_pmcs(int fd, struct pfarg_pmc __user *ureq, int count)
> +{
> + struct pfm_context *ctx;
> + struct file *filp;
> + struct pfarg_pmc pmcs[PFM_PMC_STK_ARG];
> + struct pfarg_pmc *req;
> + void *fptr;
> + unsigned long flags;
> + size_t sz;
> + int ret, fput_needed;
> +
Could this have a stack overflow on powerpc?
> + if (count < 0 || count >= PFM_MAX_ARG_COUNT(ureq))
> + return -EINVAL;
> +
> + sz = count*sizeof(*ureq);
> +
> + filp = fget_light(fd, &fput_needed);
> + if (unlikely(filp == NULL)) {
> + PFM_DBG("invalid fd %d", fd);
> + return -EBADF;
> + }
> +
> + ctx = filp->private_data;
> + ret = -EBADF;
> +
> + if (unlikely(!ctx || filp->f_op != &pfm_file_ops)) {
> + PFM_DBG("fd %d not related to perfmon", fd);
> + goto error;
> + }
> +
> + 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);
> +
> + if (copy_to_user(ureq, req, sz))
> + ret = -EFAULT;
> +
> + /*
> + * This function may be on the critical path.
> + * We want to avoid the branch if unecessary.
> + */
> + if (fptr)
> + kfree(fptr);
This comment doesn't make a lot of sense, you have to kfree(fptr) because
it could have been set in pfm_get_args() and kfree() can take a NULL
value, so why do you need a branch here at all? In fact, this branch
looks like it will always be true since this is our ptr_free from a
successful return of pfm_get_args() and this is on the success path.
> +error:
> + fput_light(filp, fput_needed);
> +
> + return ret;
> +}
> +
> +asmlinkage long sys_pfm_write_pmds(int fd, struct pfarg_pmd __user *ureq, int count)
> +{
> + struct pfm_context *ctx;
> + struct file *filp;
> + struct pfarg_pmd pmds[PFM_PMD_STK_ARG];
> + struct pfarg_pmd *req;
> + void *fptr;
> + unsigned long flags;
> + size_t sz;
> + int ret, fput_needed;
> +
> + if (count < 0 || count >= PFM_MAX_ARG_COUNT(ureq))
> + return -EINVAL;
> +
> + sz = count*sizeof(*ureq);
> +
> + filp = fget_light(fd, &fput_needed);
> + if (unlikely(filp == NULL)) {
> + PFM_DBG("invalid fd %d", fd);
> + return -EBADF;
> + }
> +
> + ctx = filp->private_data;
> + ret = -EBADF;
> +
> + if (unlikely(!ctx || filp->f_op != &pfm_file_ops)) {
> + PFM_DBG("fd %d not related to perfmon", fd);
> + goto error;
> + }
> +
> + 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, 0);
> +
> + spin_unlock_irqrestore(&ctx->lock, flags);
> +
> + if (copy_to_user(ureq, req, sz))
> + ret = -EFAULT;
> +
> + if (fptr)
> + kfree(fptr);
> +error:
> + fput_light(filp, fput_needed);
> +
> + return ret;
> +}
> +
> +asmlinkage long sys_pfm_read_pmds(int fd, struct pfarg_pmd __user *ureq, int count)
> +{
> + struct pfm_context *ctx;
> + struct file *filp;
> + struct pfarg_pmd pmds[PFM_PMD_STK_ARG];
> + struct pfarg_pmd *req;
> + void *fptr;
> + unsigned long flags;
> + size_t sz;
> + int ret, fput_needed;
> +
> + if (count < 0 || count >= PFM_MAX_ARG_COUNT(ureq))
> + return -EINVAL;
> +
> + sz = count*sizeof(*ureq);
> +
> + filp = fget_light(fd, &fput_needed);
> + if (unlikely(filp == NULL)) {
> + PFM_DBG("invalid fd %d", fd);
> + return -EBADF;
> + }
> +
> + ctx = filp->private_data;
> + ret = -EBADF;
> +
> + if (unlikely(!ctx || filp->f_op != &pfm_file_ops)) {
> + PFM_DBG("fd %d not related to perfmon", fd);
> + goto error;
> + }
> +
> + 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(req);
> +error:
> + fput_light(filp, fput_needed);
> + return ret;
> +}
> +
> +asmlinkage long sys_pfm_restart(int fd)
> +{
> + struct pfm_context *ctx;
> + struct file *filp;
> + unsigned long flags;
> + int ret, fput_needed, complete_needed;
> +
> + filp = fget_light(fd, &fput_needed);
> + if (unlikely(filp == NULL)) {
> + PFM_DBG("invalid fd %d", fd);
> + return -EBADF;
> + }
> +
> + ctx = filp->private_data;
> + ret = -EBADF;
> +
> + if (unlikely(!ctx || filp->f_op != &pfm_file_ops)) {
> + PFM_DBG("fd %d not related to perfmon", fd);
> + goto error;
> + }
> +
> + spin_lock_irqsave(&ctx->lock, flags);
> +
> + ret = pfm_check_task_state(ctx, 0, &flags);
> + if (!ret)
> + ret = __pfm_restart(ctx, &complete_needed);
> +
> + spin_unlock_irqrestore(&ctx->lock, flags);
> + /*
> + * In per-thread mode with blocking notification, i.e.
> + * ctx->flags.blocking=1, we need to defer issuing the
> + * complete to unblock the blocked monitored thread.
> + * Otherwise we have a potential deadlock due to a lock
> + * inversion between the context lock and the task_rq_lock()
> + * which can happen if one thread is in this call and the other
> + * (the monitored thread) is in the context switch code.
> + *
> + * It is safe to access the context outside the critical section
> + * because:
> + * - we are protected by the fget_light(), so the context cannot
> + * disappear.
> + * - we are protected against another thread issuing a extraneous
> + * pfm_restart() because the ctx->flags.can-restart flag has
> + * already been cleared
> + * - the restart_complete field is only touched by the context init
> + * code (happens only once) or by wait_for_completion_interruptible
> + * in __pfm_handle_work(), so this is already serialized
> + */
> + if (complete_needed)
> + complete(&ctx->restart_complete);
> +
> +error:
> + fput_light(filp, fput_needed);
> + return ret;
> +}
> +
> +asmlinkage long sys_pfm_stop(int fd)
> +{
> + struct pfm_context *ctx;
> + struct file *filp;
> + unsigned long flags;
> + int ret, fput_needed;
> +
> + filp = fget_light(fd, &fput_needed);
> + if (unlikely(filp == NULL)) {
> + PFM_DBG("invalid fd %d", fd);
> + return -EBADF;
> + }
> +
> + ctx = filp->private_data;
> + ret = -EBADF;
> +
> + if (unlikely(!ctx || filp->f_op != &pfm_file_ops)) {
> + PFM_DBG("fd %d not related to perfmon", fd);
> + goto error;
> + }
> +
> + 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);
> +
> +error:
> + fput_light(filp, fput_needed);
> + return ret;
> +}
> +
> +asmlinkage long sys_pfm_start(int fd, struct pfarg_start __user *ureq)
> +{
> + struct pfm_context *ctx;
> + struct file *filp;
> + struct pfarg_start req;
> + unsigned long flags;
> + int ret, fput_needed;
> +
> + filp = fget_light(fd, &fput_needed);
> + if (unlikely(filp == NULL)) {
> + PFM_DBG("invalid fd %d", fd);
> + return -EBADF;
> + }
> +
> + ctx = filp->private_data;
> + ret = -EBADF;
> +
> + if (unlikely(!ctx || filp->f_op != &pfm_file_ops)) {
> + PFM_DBG("fd %d not related to perfmon", fd);
> + goto error;
> + }
> +
> + /*
> + * the one argument is actually optional
> + */
> + if (ureq && copy_from_user(&req, ureq, sizeof(req)))
> + return -EFAULT;
> +
> + spin_lock_irqsave(&ctx->lock, flags);
> +
> + ret = pfm_check_task_state(ctx, PFM_CMD_STOPPED, &flags);
> + if (!ret)
> + ret = __pfm_start(ctx, ureq ? &req : NULL);
> +
> + spin_unlock_irqrestore(&ctx->lock, flags);
> +
> +error:
> + fput_light(filp, fput_needed);
> + return ret;
> +}
> +
> +asmlinkage long sys_pfm_load_context(int fd, struct pfarg_load __user *ureq)
> +{
> + struct pfm_context *ctx;
> + struct task_struct *task;
> + struct file *filp;
> + unsigned long flags;
> + struct pfarg_load req;
> + int ret, fput_needed;
> +
> + if (copy_from_user(&req, ureq, sizeof(req)))
> + return -EFAULT;
> +
> + filp = fget_light(fd, &fput_needed);
> + if (unlikely(filp == NULL)) {
> + PFM_DBG("invalid fd %d", fd);
> + return -EBADF;
> + }
> +
> + task = NULL;
> + ctx = filp->private_data;
> + ret = -EBADF;
> +
> + if (unlikely(!ctx || filp->f_op != &pfm_file_ops)) {
> + PFM_DBG("fd %d not related to perfmon", fd);
> + goto error;
> + }
> +
> + /*
> + * 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 (!ctx->flags.system) {
> + if (req.load_pid != current->pid) {
> + ret = pfm_get_task(ctx, req.load_pid, &task);
> + if (ret)
> + goto error;
> + } else
> + task = current;
> + }
This is the only call to pfm_get_task(), so it could be done by passing
"task" as the third actual instead.
David
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