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Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Browse Source 
Pull perf fixes from Ingo Molnar:
 "Most of these are uprobes race fixes from Oleg, and their preparatory
  cleanups.  (It's larger than what I'd normally send for an -rc kernel,
  but they looked significant enough to not delay them.)

  There's also an oprofile fix and an uncore PMU fix."

* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (22 commits)
  perf/x86: Disable uncore on virtualized CPUs
  oprofile, x86: Fix wrapping bug in op_x86_get_ctrl()
  ring-buffer: Check for uninitialized cpu buffer before resizing
  uprobes: Fix the racy uprobe->flags manipulation
  uprobes: Fix prepare_uprobe() race with itself
  uprobes: Introduce prepare_uprobe()
  uprobes: Fix handle_swbp() vs unregister() + register() race
  uprobes: Do not delete uprobe if uprobe_unregister() fails
  uprobes: Don't return success if alloc_uprobe() fails
  uprobes/x86: Only rep+nop can be emulated correctly
  uprobes: Simplify is_swbp_at_addr(), remove stale comments
  uprobes: Kill set_orig_insn()->is_swbp_at_addr()
  uprobes: Introduce copy_opcode(), kill read_opcode()
  uprobes: Kill set_swbp()->is_swbp_at_addr()
  uprobes: Restrict valid_vma(false) to skip VM_SHARED vmas
  uprobes: Change valid_vma() to demand VM_MAYEXEC rather than VM_EXEC
  uprobes: Change write_opcode() to use FOLL_FORCE
  uprobes: Move clear_thread_flag(TIF_UPROBE) to uprobe_notify_resume()
  uprobes: Kill UTASK_BP_HIT state
  uprobes: Fix UPROBE_SKIP_SSTEP checks in handle_swbp()
  ...
This commit is contained in:
Linus Torvalds 2012-10-24 04:07:51 +03:00
commit e17b131583
7 changed files with 174 additions and 213 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
arch/x86/kernel/cpu/perf_event_intel_uncore.c
View File

@ -2926,6 +2926,9 @@ static int __init intel_uncore_init(void)
if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
return -ENODEV;
if (cpu_has_hypervisor)
return -ENODEV;
ret = uncore_pci_init();
if (ret)
goto fail;

4
arch/x86/kernel/signal.c
View File

@ -824,10 +824,8 @@ do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
mce_notify_process();
#endif /* CONFIG_X86_64 && CONFIG_X86_MCE */
if (thread_info_flags & _TIF_UPROBE) {
clear_thread_flag(TIF_UPROBE);
if (thread_info_flags & _TIF_UPROBE)
uprobe_notify_resume(regs);
}
/* deal with pending signal delivery */
if (thread_info_flags & _TIF_SIGPENDING)

16
arch/x86/kernel/uprobes.c
View File

@ -651,31 +651,19 @@ void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
/*
* Skip these instructions as per the currently known x86 ISA.
* 0x66* { 0x90 | 0x0f 0x1f | 0x0f 0x19 | 0x87 0xc0 }
* rep=0x66*; nop=0x90
*/
static bool __skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
{
int i;
for (i = 0; i < MAX_UINSN_BYTES; i++) {
if ((auprobe->insn[i] == 0x66))
if (auprobe->insn[i] == 0x66)
continue;
if (auprobe->insn[i] == 0x90)
return true;
if (i == (MAX_UINSN_BYTES - 1))
break;
if ((auprobe->insn[i] == 0x0f) && (auprobe->insn[i+1] == 0x1f))
return true;
if ((auprobe->insn[i] == 0x0f) && (auprobe->insn[i+1] == 0x19))
return true;
if ((auprobe->insn[i] == 0x87) && (auprobe->insn[i+1] == 0xc0))
return true;
break;
}
return false;

2
arch/x86/oprofile/nmi_int.c
View File

@ -55,7 +55,7 @@ u64 op_x86_get_ctrl(struct op_x86_model_spec const *model,
val |= counter_config->extra;
event &= model->event_mask ? model->event_mask : 0xFF;
val |= event & 0xFF;
val |= (event & 0x0F00) << 24;
val |= (u64)(event & 0x0F00) << 24;
return val;
}

11
include/linux/uprobes.h
View File

@ -35,16 +35,6 @@ struct inode;
# include <asm/uprobes.h>
#endif
/* flags that denote/change uprobes behaviour */
/* Have a copy of original instruction */
#define UPROBE_COPY_INSN 0x1
/* Dont run handlers when first register/ last unregister in progress*/
#define UPROBE_RUN_HANDLER 0x2
/* Can skip singlestep */
#define UPROBE_SKIP_SSTEP 0x4
struct uprobe_consumer {
int (*handler)(struct uprobe_consumer *self, struct pt_regs *regs);
/*
@ -59,7 +49,6 @@ struct uprobe_consumer {
#ifdef CONFIG_UPROBES
enum uprobe_task_state {
UTASK_RUNNING,
UTASK_BP_HIT,
UTASK_SSTEP,
UTASK_SSTEP_ACK,
UTASK_SSTEP_TRAPPED,

347
kernel/events/uprobes.c
View File

@ -78,15 +78,23 @@ static struct mutex uprobes_mmap_mutex[UPROBES_HASH_SZ];
*/
static atomic_t uprobe_events = ATOMIC_INIT(0);
/* Have a copy of original instruction */
#define UPROBE_COPY_INSN 0
/* Dont run handlers when first register/ last unregister in progress*/
#define UPROBE_RUN_HANDLER 1
/* Can skip singlestep */
#define UPROBE_SKIP_SSTEP 2
struct uprobe {
struct rb_node rb_node; /* node in the rb tree */
atomic_t ref;
struct rw_semaphore consumer_rwsem;
struct mutex copy_mutex; /* TODO: kill me and UPROBE_COPY_INSN */
struct list_head pending_list;
struct uprobe_consumer *consumers;
struct inode *inode; /* Also hold a ref to inode */
loff_t offset;
int flags;
unsigned long flags;
struct arch_uprobe arch;
};
@ -100,17 +108,12 @@ struct uprobe {
*/
static bool valid_vma(struct vm_area_struct *vma, bool is_register)
{
if (!vma->vm_file)
return false;
vm_flags_t flags = VM_HUGETLB | VM_MAYEXEC | VM_SHARED;
if (!is_register)
return true;
if (is_register)
flags |= VM_WRITE;
if ((vma->vm_flags & (VM_HUGETLB|VM_READ|VM_WRITE|VM_EXEC|VM_SHARED))
== (VM_READ|VM_EXEC))
return true;
return false;
return vma->vm_file && (vma->vm_flags & flags) == VM_MAYEXEC;
}
static unsigned long offset_to_vaddr(struct vm_area_struct *vma, loff_t offset)
@ -193,19 +196,44 @@ bool __weak is_swbp_insn(uprobe_opcode_t *insn)
return *insn == UPROBE_SWBP_INSN;
}
static void copy_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *opcode)
{
void *kaddr = kmap_atomic(page);
memcpy(opcode, kaddr + (vaddr & ~PAGE_MASK), UPROBE_SWBP_INSN_SIZE);
kunmap_atomic(kaddr);
}
static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode)
{
uprobe_opcode_t old_opcode;
bool is_swbp;
copy_opcode(page, vaddr, &old_opcode);
is_swbp = is_swbp_insn(&old_opcode);
if (is_swbp_insn(new_opcode)) {
if (is_swbp) /* register: already installed? */
return 0;
} else {
if (!is_swbp) /* unregister: was it changed by us? */
return 0;
}
return 1;
}
/*
* NOTE:
* Expect the breakpoint instruction to be the smallest size instruction for
* the architecture. If an arch has variable length instruction and the
* breakpoint instruction is not of the smallest length instruction
* supported by that architecture then we need to modify read_opcode /
* supported by that architecture then we need to modify is_swbp_at_addr and
* write_opcode accordingly. This would never be a problem for archs that
* have fixed length instructions.
*/
/*
* write_opcode - write the opcode at a given virtual address.
* @auprobe: arch breakpointing information.
* @mm: the probed process address space.
* @vaddr: the virtual address to store the opcode.
* @opcode: opcode to be written at @vaddr.
@ -216,8 +244,8 @@ bool __weak is_swbp_insn(uprobe_opcode_t *insn)
* For mm @mm, write the opcode at @vaddr.
* Return 0 (success) or a negative errno.
*/
static int write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
unsigned long vaddr, uprobe_opcode_t opcode)
static int write_opcode(struct mm_struct *mm, unsigned long vaddr,
uprobe_opcode_t opcode)
{
struct page *old_page, *new_page;
void *vaddr_old, *vaddr_new;
@ -226,10 +254,14 @@ static int write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
retry:
/* Read the page with vaddr into memory */
ret = get_user_pages(NULL, mm, vaddr, 1, 0, 0, &old_page, &vma);
ret = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &old_page, &vma);
if (ret <= 0)
return ret;
ret = verify_opcode(old_page, vaddr, &opcode);
if (ret <= 0)
goto put_old;
ret = -ENOMEM;
new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr);
if (!new_page)
@ -263,63 +295,6 @@ put_old:
return ret;
}
/**
* read_opcode - read the opcode at a given virtual address.
* @mm: the probed process address space.
* @vaddr: the virtual address to read the opcode.
* @opcode: location to store the read opcode.
*
* Called with mm->mmap_sem held (for read and with a reference to
* mm.
*
* For mm @mm, read the opcode at @vaddr and store it in @opcode.
* Return 0 (success) or a negative errno.
*/
static int read_opcode(struct mm_struct *mm, unsigned long vaddr, uprobe_opcode_t *opcode)
{
struct page *page;
void *vaddr_new;
int ret;
ret = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &page, NULL);
if (ret <= 0)
return ret;
vaddr_new = kmap_atomic(page);
vaddr &= ~PAGE_MASK;
memcpy(opcode, vaddr_new + vaddr, UPROBE_SWBP_INSN_SIZE);
kunmap_atomic(vaddr_new);
put_page(page);
return 0;
}
static int is_swbp_at_addr(struct mm_struct *mm, unsigned long vaddr)
{
uprobe_opcode_t opcode;
int result;
if (current->mm == mm) {
pagefault_disable();
result = __copy_from_user_inatomic(&opcode, (void __user*)vaddr,
sizeof(opcode));
pagefault_enable();
if (likely(result == 0))
goto out;
}
result = read_opcode(mm, vaddr, &opcode);
if (result)
return result;
out:
if (is_swbp_insn(&opcode))
return 1;
return 0;
}
/**
* set_swbp - store breakpoint at a given address.
* @auprobe: arch specific probepoint information.
@ -331,18 +306,7 @@ out:
*/
int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
{
int result;
/*
* See the comment near uprobes_hash().
*/
result = is_swbp_at_addr(mm, vaddr);
if (result == 1)
return 0;
if (result)
return result;
return write_opcode(auprobe, mm, vaddr, UPROBE_SWBP_INSN);
return write_opcode(mm, vaddr, UPROBE_SWBP_INSN);
}
/**
@ -357,16 +321,7 @@ int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned
int __weak
set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
{
int result;
result = is_swbp_at_addr(mm, vaddr);
if (!result)
return -EINVAL;
if (result != 1)
return result;
return write_opcode(auprobe, mm, vaddr, *(uprobe_opcode_t *)auprobe->insn);
return write_opcode(mm, vaddr, *(uprobe_opcode_t *)auprobe->insn);
}
static int match_uprobe(struct uprobe *l, struct uprobe *r)
@ -473,7 +428,7 @@ static struct uprobe *insert_uprobe(struct uprobe *uprobe)
spin_unlock(&uprobes_treelock);
/* For now assume that the instruction need not be single-stepped */
uprobe->flags |= UPROBE_SKIP_SSTEP;
__set_bit(UPROBE_SKIP_SSTEP, &uprobe->flags);
return u;
}
@ -495,6 +450,7 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
uprobe->inode = igrab(inode);
uprobe->offset = offset;
init_rwsem(&uprobe->consumer_rwsem);
mutex_init(&uprobe->copy_mutex);
/* add to uprobes_tree, sorted on inode:offset */
cur_uprobe = insert_uprobe(uprobe);
@ -515,7 +471,7 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
{
struct uprobe_consumer *uc;
if (!(uprobe->flags & UPROBE_RUN_HANDLER))
if (!test_bit(UPROBE_RUN_HANDLER, &uprobe->flags))
return;
down_read(&uprobe->consumer_rwsem);
@ -621,29 +577,43 @@ static int copy_insn(struct uprobe *uprobe, struct file *filp)
return __copy_insn(mapping, filp, uprobe->arch.insn, bytes, uprobe->offset);
}
/*
* How mm->uprobes_state.count gets updated
* uprobe_mmap() increments the count if
* - it successfully adds a breakpoint.
* - it cannot add a breakpoint, but sees that there is a underlying
* breakpoint (via a is_swbp_at_addr()).
*
* uprobe_munmap() decrements the count if
* - it sees a underlying breakpoint, (via is_swbp_at_addr)
* (Subsequent uprobe_unregister wouldnt find the breakpoint
* unless a uprobe_mmap kicks in, since the old vma would be
* dropped just after uprobe_munmap.)
*
* uprobe_register increments the count if:
* - it successfully adds a breakpoint.
*
* uprobe_unregister decrements the count if:
* - it sees a underlying breakpoint and removes successfully.
* (via is_swbp_at_addr)
* (Subsequent uprobe_munmap wouldnt find the breakpoint
* since there is no underlying breakpoint after the
* breakpoint removal.)
*/
static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
struct mm_struct *mm, unsigned long vaddr)
{
int ret = 0;
if (test_bit(UPROBE_COPY_INSN, &uprobe->flags))
return ret;
mutex_lock(&uprobe->copy_mutex);
if (test_bit(UPROBE_COPY_INSN, &uprobe->flags))
goto out;
ret = copy_insn(uprobe, file);
if (ret)
goto out;
ret = -ENOTSUPP;
if (is_swbp_insn((uprobe_opcode_t *)uprobe->arch.insn))
goto out;
ret = arch_uprobe_analyze_insn(&uprobe->arch, mm, vaddr);
if (ret)
goto out;
/* write_opcode() assumes we don't cross page boundary */
BUG_ON((uprobe->offset & ~PAGE_MASK) +
UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
smp_wmb(); /* pairs with rmb() in find_active_uprobe() */
set_bit(UPROBE_COPY_INSN, &uprobe->flags);
out:
mutex_unlock(&uprobe->copy_mutex);
return ret;
}
static int
install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
struct vm_area_struct *vma, unsigned long vaddr)
@ -661,24 +631,9 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
if (!uprobe->consumers)
return 0;
if (!(uprobe->flags & UPROBE_COPY_INSN)) {
ret = copy_insn(uprobe, vma->vm_file);
if (ret)
return ret;
if (is_swbp_insn((uprobe_opcode_t *)uprobe->arch.insn))
return -ENOTSUPP;
ret = arch_uprobe_analyze_insn(&uprobe->arch, mm, vaddr);
if (ret)
return ret;
/* write_opcode() assumes we don't cross page boundary */
BUG_ON((uprobe->offset & ~PAGE_MASK) +
UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
uprobe->flags |= UPROBE_COPY_INSN;
}
ret = prepare_uprobe(uprobe, vma->vm_file, mm, vaddr);
if (ret)
return ret;
/*
* set MMF_HAS_UPROBES in advance for uprobe_pre_sstep_notifier(),
@ -697,15 +652,15 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
return ret;
}
static void
static int
remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vaddr)
{
/* can happen if uprobe_register() fails */
if (!test_bit(MMF_HAS_UPROBES, &mm->flags))
return;
return 0;
set_bit(MMF_RECALC_UPROBES, &mm->flags);
set_orig_insn(&uprobe->arch, mm, vaddr);
return set_orig_insn(&uprobe->arch, mm, vaddr);
}
/*
@ -820,7 +775,7 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
struct mm_struct *mm = info->mm;
struct vm_area_struct *vma;
if (err)
if (err && is_register)
goto free;
down_write(&mm->mmap_sem);
@ -836,7 +791,7 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
if (is_register)
err = install_breakpoint(uprobe, mm, vma, info->vaddr);
else
remove_breakpoint(uprobe, mm, info->vaddr);
err |= remove_breakpoint(uprobe, mm, info->vaddr);
unlock:
up_write(&mm->mmap_sem);
@ -893,13 +848,15 @@ int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *
mutex_lock(uprobes_hash(inode));
uprobe = alloc_uprobe(inode, offset);
if (uprobe && !consumer_add(uprobe, uc)) {
if (!uprobe) {
ret = -ENOMEM;
} else if (!consumer_add(uprobe, uc)) {
ret = __uprobe_register(uprobe);
if (ret) {
uprobe->consumers = NULL;
__uprobe_unregister(uprobe);
} else {
uprobe->flags |= UPROBE_RUN_HANDLER;
set_bit(UPROBE_RUN_HANDLER, &uprobe->flags);
}
}
@ -932,7 +889,7 @@ void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consume
if (consumer_del(uprobe, uc)) {
if (!uprobe->consumers) {
__uprobe_unregister(uprobe);
uprobe->flags &= ~UPROBE_RUN_HANDLER;
clear_bit(UPROBE_RUN_HANDLER, &uprobe->flags);
}
}
@ -1393,10 +1350,11 @@ bool uprobe_deny_signal(void)
*/
static bool can_skip_sstep(struct uprobe *uprobe, struct pt_regs *regs)
{
if (arch_uprobe_skip_sstep(&uprobe->arch, regs))
return true;
uprobe->flags &= ~UPROBE_SKIP_SSTEP;
if (test_bit(UPROBE_SKIP_SSTEP, &uprobe->flags)) {
if (arch_uprobe_skip_sstep(&uprobe->arch, regs))
return true;
clear_bit(UPROBE_SKIP_SSTEP, &uprobe->flags);
}
return false;
}
@ -1419,6 +1377,30 @@ static void mmf_recalc_uprobes(struct mm_struct *mm)
clear_bit(MMF_HAS_UPROBES, &mm->flags);
}
static int is_swbp_at_addr(struct mm_struct *mm, unsigned long vaddr)
{
struct page *page;
uprobe_opcode_t opcode;
int result;
pagefault_disable();
result = __copy_from_user_inatomic(&opcode, (void __user*)vaddr,
sizeof(opcode));
pagefault_enable();
if (likely(result == 0))
goto out;
result = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &page, NULL);
if (result < 0)
return result;
copy_opcode(page, vaddr, &opcode);
put_page(page);
out:
return is_swbp_insn(&opcode);
}
static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp)
{
struct mm_struct *mm = current->mm;
@ -1489,38 +1471,41 @@ static void handle_swbp(struct pt_regs *regs)
}
return;
}
/*
* TODO: move copy_insn/etc into _register and remove this hack.
* After we hit the bp, _unregister + _register can install the
* new and not-yet-analyzed uprobe at the same address, restart.
*/
smp_rmb(); /* pairs with wmb() in install_breakpoint() */
if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags)))
goto restart;
utask = current->utask;
if (!utask) {
utask = add_utask();
/* Cannot allocate; re-execute the instruction. */
if (!utask)
goto cleanup_ret;
goto restart;
}
utask->active_uprobe = uprobe;
handler_chain(uprobe, regs);
if (uprobe->flags & UPROBE_SKIP_SSTEP && can_skip_sstep(uprobe, regs))
goto cleanup_ret;
utask->state = UTASK_SSTEP;
handler_chain(uprobe, regs);
if (can_skip_sstep(uprobe, regs))
goto out;
if (!pre_ssout(uprobe, regs, bp_vaddr)) {
arch_uprobe_enable_step(&uprobe->arch);
utask->active_uprobe = uprobe;
utask->state = UTASK_SSTEP;
return;
}
cleanup_ret:
if (utask) {
utask->active_uprobe = NULL;
utask->state = UTASK_RUNNING;
}
if (!(uprobe->flags & UPROBE_SKIP_SSTEP))
/*
* cannot singlestep; cannot skip instruction;
* re-execute the instruction.
*/
instruction_pointer_set(regs, bp_vaddr);
restart:
/*
* cannot singlestep; cannot skip instruction;
* re-execute the instruction.
*/
instruction_pointer_set(regs, bp_vaddr);
out:
put_uprobe(uprobe);
}
@ -1552,13 +1537,12 @@ static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs)
}
/*
* On breakpoint hit, breakpoint notifier sets the TIF_UPROBE flag. (and on
* subsequent probe hits on the thread sets the state to UTASK_BP_HIT) and
* allows the thread to return from interrupt.
* On breakpoint hit, breakpoint notifier sets the TIF_UPROBE flag and
* allows the thread to return from interrupt. After that handle_swbp()
* sets utask->active_uprobe.
*
* On singlestep exception, singlestep notifier sets the TIF_UPROBE flag and
* also sets the state to UTASK_SSTEP_ACK and allows the thread to return from
* interrupt.
* On singlestep exception, singlestep notifier sets the TIF_UPROBE flag
* and allows the thread to return from interrupt.
*
* While returning to userspace, thread notices the TIF_UPROBE flag and calls
* uprobe_notify_resume().
@ -1567,11 +1551,13 @@ void uprobe_notify_resume(struct pt_regs *regs)
{
struct uprobe_task *utask;
clear_thread_flag(TIF_UPROBE);
utask = current->utask;
if (!utask || utask->state == UTASK_BP_HIT)
handle_swbp(regs);
else
if (utask && utask->active_uprobe)
handle_singlestep(utask, regs);
else
handle_swbp(regs);
}
/*
@ -1580,17 +1566,10 @@ void uprobe_notify_resume(struct pt_regs *regs)
*/
int uprobe_pre_sstep_notifier(struct pt_regs *regs)
{
struct uprobe_task *utask;
if (!current->mm || !test_bit(MMF_HAS_UPROBES, &current->mm->flags))
return 0;
utask = current->utask;
if (utask)
utask->state = UTASK_BP_HIT;
set_thread_flag(TIF_UPROBE);
return 1;
}

4
kernel/trace/ring_buffer.c
View File

@ -1567,6 +1567,10 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
put_online_cpus();
} else {
/* Make sure this CPU has been intitialized */
if (!cpumask_test_cpu(cpu_id, buffer->cpumask))
goto out;
cpu_buffer = buffer->buffers[cpu_id];
if (nr_pages == cpu_buffer->nr_pages)