On Tue, 29 May 2007, Stephane Eranian wrote:
> --- linux-2.6.22.base/perfmon/perfmon_res.c 1969-12-31 16:00:00.000000000 -0800
> +++ linux-2.6.22/perfmon/perfmon_res.c 2007-05-29 03:24:14.000000000 -0700
> @@ -0,0 +1,344 @@
> +/*
> + * perfmon_res.c: perfmon2 resource allocations
> + *
> + * 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/spinlock.h>
> +#include <linux/perfmon.h>
> +#include <linux/module.h>
> +
> +/*
> + * global information about all sessions
> + * mostly used to synchronize between system wide and per-process
> + */
> +struct pfm_sessions {
> + u32 pfs_task_sessions;/* #num loaded per-thread sessions */
> + size_t pfs_smpl_buffer_mem_cur; /* current smpl buf mem usage */
> + cpumask_t pfs_sys_cpumask; /* bitmask of used cpus (system-wide) */
> +};
> +
> +static struct pfm_sessions pfm_sessions;
> +
> +static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pfm_sessions_lock);
> +
> +/*
> + * sampling buffer allocated by perfmon must be
> + * checked against max usage thresholds for security
> + * reasons.
> + *
> + * The first level check is against the system wide limit
> + * as indicated by the system administrator in /proc/sys/kernel/perfmon
> + *
> + * The second level check is on a per-process basis using
> + * RLIMIT_MEMLOCK limit.
> + *
> + * Operating on the current task only.
> + */
> +int pfm_reserve_buf_space(size_t size)
> +{
> + struct mm_struct *mm;
> + unsigned long locked;
> + unsigned long buf_mem, buf_mem_max;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&pfm_sessions_lock, flags);
> +
> + /*
> + * check against global buffer limit
> + */
> + buf_mem_max = pfm_controls.smpl_buffer_mem_max;
> + buf_mem = pfm_sessions.pfs_smpl_buffer_mem_cur + size;
> +
> + if (buf_mem <= buf_mem_max) {
> + pfm_sessions.pfs_smpl_buffer_mem_cur = buf_mem;
> +
> + PFM_DBG("buf_mem_max=%lu current_buf_mem=%lu",
> + buf_mem_max,
> + buf_mem);
> + }
> + spin_unlock_irqrestore(&pfm_sessions_lock, flags);
> +
> + if (buf_mem > buf_mem_max) {
> + PFM_DBG("smpl buffer memory threshold reached");
> + return -ENOMEM;
> + }
> +
> + /*
> + * check against RLIMIT_MEMLOCK
> + */
> + mm = get_task_mm(current);
> +
> + down_write(&mm->mmap_sem);
> +
> + locked = mm->locked_vm << PAGE_SHIFT;
> + locked += size;
> +
> + if (locked > current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur) {
> +
> + PFM_DBG("RLIMIT_MEMLOCK reached ask_locked=%lu rlim_cur=%lu",
> + locked,
> + current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur);
> +
> + up_write(&mm->mmap_sem);
> + mmput(mm);
> + goto unres;
> + }
> +
> + mm->locked_vm = locked >> PAGE_SHIFT;
> +
> + up_write(&mm->mmap_sem);
> +
> + mmput(mm);
> +
> + return 0;
> +
> +unres:
> + /*
> + * remove global buffer memory allocation
> + */
> + spin_lock_irqsave(&pfm_sessions_lock, flags);
> +
> + pfm_sessions.pfs_smpl_buffer_mem_cur -= size;
> +
> + spin_unlock_irqrestore(&pfm_sessions_lock, flags);
> +
> + return -ENOMEM;
> +}
> +/*
> + *There exist multiple paths leading to this function. We need to
> + * be very careful withlokcing on the mmap_sem as it may already be
> + * held by the time we come here.
> + * The following paths exist:
> + *
> + * exit path:
> + * sys_exit_group
> + * do_group_exit
> + * do_exit
> + * exit_mm
> + * mmput
> + * exit_mmap
> + * remove_vma
> + * fput
> + * __fput
> + * pfm_close
> + * __pfm_close
> + * pfm_context_free
> + * pfm_release_buf_space
> + * munmap path:
> + * sys_munmap
> + * do_munmap
> + * remove_vma
> + * fput
> + * __fput
> + * pfm_close
> + * __pfm_close
> + * pfm_context_free
> + * pfm_release_buf_space
> + *
> + * close path:
> + * sys_close
> + * filp_close
> + * fput
> + * __fput
> + * pfm_close
> + * __pfm_close
> + * pfm_context_free
> + * pfm_release_buf_space
> + *
> + * The issue is that on the munmap() path, the mmap_sem is already held
> + * in write-mode by the time we come here. To avoid the deadlock, we need
> + * to know where we are coming from and skip down_write(). If is fairly
> + * difficult to know this because of the lack of good hooks and
> + * the fact that, there may not have been any mmap() of the sampling buffer
> + * (i.e. create_context() followed by close() or exit()).
> + *
> + * We use a set flag ctx->flags.mmap_nlock which is toggle in the vm_ops
> + * callback in remove_vma() which is called systematically for the call, so
> + * on all but the pure close() path. The exit path does not already hold
> + * the lock but this is exit so there is no task->mm by the time we come here.
> + *
> + * The mmap_nlock is set only when unmapping and this is the LAST reference
> + * to the file (i.e., close() followed by munmap()).
> + */
> +void pfm_release_buf_space(struct pfm_context *ctx, size_t size)
> +{
> + unsigned long flags;
> + struct mm_struct *mm;
> +
> + mm = get_task_mm(current);
> + if (mm) {
> + if (ctx->flags.mmap_nlock == 0) {
> + PFM_DBG("doing down_write");
> + down_write(&mm->mmap_sem);
> + }
> +
> + mm->locked_vm -= size >> PAGE_SHIFT;
> +
> + PFM_DBG("locked_vm=%lu size=%zu", mm->locked_vm, size);
> +
> + if (ctx->flags.mmap_nlock == 0)
> + up_write(&mm->mmap_sem);
No chance of ctx->flags.mmap_nlock getting changed between down_write()
and up_write() for mm->mmap_sem, correct?
> +
> + mmput(mm);
> + }
> +
> + spin_lock_irqsave(&pfm_sessions_lock, flags);
> +
> + pfm_sessions.pfs_smpl_buffer_mem_cur -= size;
> +
> + spin_unlock_irqrestore(&pfm_sessions_lock, flags);
> +}
> +
> +int pfm_reserve_session(int is_system, u32 cpu)
> +{
> + unsigned long flags;
> + u32 nsys_cpus;
int ret = 0;
> +
> + /*
> + * validy checks on cpu_mask have been done upstream
> + */
> + spin_lock_irqsave(&pfm_sessions_lock, flags);
> +
> + nsys_cpus = cpus_weight(pfm_sessions.pfs_sys_cpumask);
> +
> + PFM_DBG("in sys=%u task=%u is_sys=%d cpu=%u",
> + nsys_cpus,
> + pfm_sessions.pfs_task_sessions,
> + is_system,
> + cpu);
> +
> + if (is_system) {
> + /*
> + * cannot mix system wide and per-task sessions
> + */
> + if (pfm_sessions.pfs_task_sessions > 0) {
> + PFM_DBG("%u conflicting task_sessions",
> + pfm_sessions.pfs_task_sessions);
ret = -EBUSY;
> + goto abort;
> + }
> +
> + if (cpu_isset(cpu, pfm_sessions.pfs_sys_cpumask)) {
> + PFM_DBG("conflicting session on CPU%u", cpu);
ret = -EBUSY;
> + goto abort;
> + }
> +
> + PFM_DBG("reserved session on CPU%u", cpu);
> +
> + cpu_set(cpu, pfm_sessions.pfs_sys_cpumask);
> + nsys_cpus++;
> + } else {
> + if (nsys_cpus)
> + goto abort;
if (nsys_cpus) {
ret = -EBUSY;
goto abort;
}
> + pfm_sessions.pfs_task_sessions++;
> + }
> +
> + PFM_DBG("out sys=%u task=%u is_sys=%d cpu=%u",
> + nsys_cpus,
> + pfm_sessions.pfs_task_sessions,
> + is_system,
> + cpu);
> +
> + spin_unlock_irqrestore(&pfm_sessions_lock, flags);
> +
> + return 0;
Get rid of those two lines.
> +
> +abort:
> + spin_unlock_irqrestore(&pfm_sessions_lock, flags);
> +
> + return -EBUSY;
return ret;
> +}
> +
> +/*
> + * called from __pfm_unload_context()
> + */
> +int pfm_release_session(int is_system, u32 cpu)
> +{
> + unsigned long flags;
> +
> + spin_lock_irqsave(&pfm_sessions_lock, flags);
> +
> + PFM_DBG("in sys_sessions=%u task_sessions=%u syswide=%d cpu=%u",
> + cpus_weight(pfm_sessions.pfs_sys_cpumask),
> + pfm_sessions.pfs_task_sessions,
> + is_system, cpu);
> +
> + if (is_system)
> + cpu_clear(cpu, pfm_sessions.pfs_sys_cpumask);
> + else
> + pfm_sessions.pfs_task_sessions--;
> +
> + PFM_DBG("out sys_sessions=%u task_sessions=%u syswide=%d cpu=%u",
> + cpus_weight(pfm_sessions.pfs_sys_cpumask),
> + pfm_sessions.pfs_task_sessions,
> + is_system, cpu);
> +
> + spin_unlock_irqrestore(&pfm_sessions_lock, flags);
> + return 0;
> +}
> +
> +/*
> + * called from perfmon_sysfs.c:
> + * what=0 : pfs_task_sessions
> + * what=1 : cpus_weight(pfs_sys_cpumask)
> + * what=2 : smpl_buffer_mem_cur
> + * what=3 : pmu model name
> + *
> + * return number of bytes written into buf (up to sz)
> + */
> +ssize_t pfm_sysfs_session_show(char *buf, size_t sz, int what)
> +{
> + unsigned long flags;
> +
> + if (pfm_pmu_conf) {
> + spin_lock_irqsave(&pfm_sessions_lock, flags);
> + switch (what) {
> + case 0: snprintf(buf, sz, "%u\n", pfm_sessions.pfs_task_sessions);
> + break;
> + case 1: snprintf(buf, sz, "%d\n", cpus_weight(pfm_sessions.pfs_sys_cpumask));
> + break;
> + case 2: snprintf(buf, sz, "%zu\n", pfm_sessions.pfs_smpl_buffer_mem_cur);
> + break;
> + case 3:
> + snprintf(buf, sz, "%s\n", pfm_pmu_conf->pmu_name);
> + }
These values need associated enums and used in patch 4.
David
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