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  1. 16 6月, 2012 12 次提交
  3. 08 6月, 2012 1 次提交
  5. 06 6月, 2012 7 次提交
    • O
      uprobes: Kill uprobes_srcu/uprobe_srcu_id · 778b032d
      由 Oleg Nesterov 提交于 
      Kill the no longer needed uprobes_srcu/uprobe_srcu_id code.

It doesn't really work anyway. synchronize_srcu() can only
synchronize with the code "inside" the
srcu_read_lock/srcu_read_unlock section, while
uprobe_pre_sstep_notifier() does srcu_read_lock() _after_ we
already hit the breakpoint.

I guess this probably works "in practice". synchronize_srcu() is
slow and it implies synchronize_sched(), and the probed task
enters the non- preemptible section at the start of exception
handler. Still this is not right at least in theory, and
task->uprobe_srcu_id blows task_struct.
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Acked-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120529193008.GG8057@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      778b032d
    • O
      uprobes: Teach handle_swbp() to rely on "is_swbp" rather than uprobes_srcu · 56bb4cf6
      由 Oleg Nesterov 提交于 
      Currently handle_swbp() assumes that it can't race with
unregister, so it roughly does:

	if (find_uprobe(vaddr))
		process_uprobe();
	else
		send_sig(SIGTRAP);

This relies on the not-really-working uprobes_srcu code we are
going to remove, see the next patch.

With this patch we rely on the result of
is_swbp_at_addr(bp_vaddr) if find_uprobe() fails.

If is_swbp == 1, then we hit the normal int3, we should send
SIGTRAP.

If is_swbp == 0, we raced with uprobe_unregister(), we simply
restart this insn again.

The "difficult" case is is_swbp == -EFAULT, when we can't read
this memory. In this case I think we should restart too, and
this is more correct compared to the current code which sends
SIGTRAP.

Ignoring ENOMEM/etc from get_user_pages(), this can only happen
if another thread unmaps this memory before find_active_uprobe()
takes mmap_sem. It would be better to pretend it was unmapped
before this insn was executed, restart, and get SIGSEGV.
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Acked-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120529192947.GF8057@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      56bb4cf6
    • O
      uprobes: Change register_for_each_vma() to take mm->mmap_sem for writing · 77fc4af1
      由 Oleg Nesterov 提交于 
      Change register_for_each_vma() to take mm->mmap_sem for writing.
This is a bit unfortunate but hopefully not too bad, this is the
slow path anyway.

This is needed to ensure that find_active_uprobe() can not race
with uprobe_register() which adds the new bp at the same
bp_vaddr, after find_uprobe() fails and before
is_swbp_at_addr_fast() checks the memory.

IOW, this is needed to ensure that if find_active_uprobe()
returns NULL but is_swbp == true, we can safely assume that it
was the "normal" int3 and we should send SIGTRAP.

There is another reason for this change. We are going to replace
uprobes_state->count with MMF_ flags set by register/unregister
and cleared by find_active_uprobe(), and set/clear shouldn't
race with each other.
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Acked-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120529192928.GE8057@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      77fc4af1
    • O
      uprobes: Teach find_active_uprobe() to provide the "is_swbp" info · d790d346
      由 Oleg Nesterov 提交于 
      A separate patch to simplify the review, and for the
documentation.

The patch adds another "int *is_swbp" argument to
find_active_uprobe(), so far its only caller doesn't use this
info.

With this patch find_active_uprobe() additionally does:

	- if find_vma() + ->vm_start check fails, *is_swbp = -EFAULT

	- otherwise, if valid_vma() + find_uprobe() fails, it holds
	  the result of is_swbp_at_addr(), can be negative too. The
	  latter is only possible if we raced with another thread
	  which did munmap/etc after we hit this bp.

IOW. If find_active_uprobe(&is_swbp) returns NULL, the caller
can look at is_swbp to figure out whether the current insn is bp
or not, or detect the race with another thread if it is
negative.

Note: I think that performance-wise this change is fine. This
adds is_swbp_at_addr(), but only if we raced with
uprobe_unregister() or if we hit the "normal" int3 but this mm
has uprobes as well. And even in this case the slow
read_opcode() path is very unlikely, this insn recently
triggered do_int3(), __copy_from_user_inatomic() shouldn't fail
in the likely case.
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Acked-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120529192914.GD8057@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      d790d346
    • O
      uprobes: Introduce find_active_uprobe() helper · 3a9ea052
      由 Oleg Nesterov 提交于 
      No functional changes. Move the "find uprobe" code from
handle_swbp() to the new helper, find_active_uprobe().

Note: with or without this change, the find-active-uprobe logic
is not exactly right. We can race with another thread which
unmaps the memory with the valid uprobe before we take
mm->mmap_sem. We can't find this uprobe simply because
find_vma() fails. In this case we wrongly assume that this trap
was not caused by uprobe and send the erroneous SIGTRAP. See the
next changes.
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Acked-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120529192857.GC8057@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      3a9ea052
    • O
      uprobes: Change read_opcode() to use FOLL_FORCE · a3d7bb47
      由 Oleg Nesterov 提交于 
      set_orig_insn()->read_opcode() should not fail if the probed
task did mprotect() after uprobe_register(), change it to use
FOLL_FORCE. Without FOLL_WRITE this doesn't have any "side"
effect but allows to read the !VM_READ memory.

There is another reason for this change, we are going to use
is_swbp_at_addr() from handle_swbp() which can race with another
thread doing mprotect().
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Acked-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120529192759.GB8057@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      a3d7bb47
    • O
      uprobes: Optimize is_swbp_at_addr() for current->mm · c00b2750
      由 Oleg Nesterov 提交于 
      Change is_swbp_at_addr() to try to avoid the costly
read_opcode() if mm == current->mm, __copy_from_user_inatomic()
should succeed in the likely case.

Currently this optimization is not important, but we are going
to add more is_swbp_at_addr(current->mm) callers.
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Acked-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120529192744.GA8057@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      c00b2750
  7. 14 4月, 2012 2 次提交
    • S
      uprobes/core: Decrement uprobe count before the pages are unmapped · cbc91f71
      由 Srikar Dronamraju 提交于 
      Uprobes has a callback (uprobe_munmap()) in the unmap path to
maintain the uprobes count.

In the exit path this callback gets called in unlink_file_vma().
However by the time unlink_file_vma() is called, the pages would
have been unmapped (in unmap_vmas()) and the task->rss_stat counts
accounted (in zap_pte_range()).

If the exiting process has probepoints, uprobe_munmap() checks if
the breakpoint instruction was around before decrementing the probe
count.

This results in a file backed page being reread by uprobe_munmap()
and hence it does not find the breakpoint.

This patch fixes this problem by moving the callback to
unmap_single_vma(). Since unmap_single_vma() may not unmap the
complete vma, add start and end parameters to uprobe_munmap().

This bug became apparent courtesy of commit c3f0327f
("mm: add rss counters consistency check").
Signed-off-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@linux.vnet.ibm.com>
Cc: Linux-mm <linux-mm@kvack.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120411103527.23245.9835.sendpatchset@srdronam.in.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      cbc91f71
    • S
      uprobes/core: Make background page replacement logic account for rss_stat counters · 7396fa81
      由 Srikar Dronamraju 提交于 
      Background page replacement logic adds a new anonymous page
instead of a file backed (while inserting a breakpoint) /
anonymous page (while removing a breakpoint).

Hence the uprobes logic should take care to update the
task->ss_stat counters accordingly.

This bug became apparent courtesy of commit c3f0327f
("mm: add rss counters consistency check").
Signed-off-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@linux.vnet.ibm.com>
Cc: Linux-mm <linux-mm@kvack.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120411103516.23245.2700.sendpatchset@srdronam.in.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      7396fa81
  9. 31 3月, 2012 2 次提交
    • S
      uprobes/core: Optimize probe hits with the help of a counter · 682968e0
      由 Srikar Dronamraju 提交于 
      Maintain a per-mm counter: number of uprobes that are inserted
on this process address space.

This counter can be used at probe hit time to determine if we
need a lookup in the uprobes rbtree. Everytime a probe gets
inserted successfully, the probe count is incremented and
everytime a probe gets removed, the probe count is decremented.

The new uprobe_munmap hook ensures the count is correct on a
unmap or remap of a region. We expect that once a
uprobe_munmap() is called, the vma goes away.  So
uprobe_unregister() finding a probe to unregister would either
mean unmap event hasnt occurred yet or a mmap event on the same
executable file occured after a unmap event.

Additionally, uprobe_mmap hook now also gets called:

 a. on every executable vma that is COWed at fork.
 b. a vma of interest is newly mapped; breakpoint insertion also
    happens at the required address.

On process creation, make sure the probes count in the child is
set correctly.

Special cases that are taken care include:

 a. mremap
 b. VM_DONTCOPY vmas on fork()
 c. insertion/removal races in the parent during fork().
Signed-off-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@linux.vnet.ibm.com>
Cc: Linux-mm <linux-mm@kvack.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120330182646.10018.85805.sendpatchset@srdronam.in.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      682968e0
    • S
      uprobes/core: Allocate XOL slots for uprobes use · d4b3b638
      由 Srikar Dronamraju 提交于 
      Uprobes executes the original instruction at a probed location
out of line. For this, we allocate a page (per mm) upon the
first uprobe hit, in the process user address space, divide it
into slots that are used to store the actual instructions to be
singlestepped. These slots are known as xol (execution out of
line) slots.

Care is taken to ensure that the allocation is in an unmapped
area as close to the top of the user address space as possible,
with appropriate permission settings to keep selinux like
frameworks happy.

Upon a uprobe hit, a free slot is acquired, and is released
after the singlestep completes.

Lots of improvements courtesy suggestions/inputs from Peter and
Oleg.

[ Folded a fix for build issue on powerpc fixed and reported by
  Stephen Rothwell. ]
Signed-off-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@linux.vnet.ibm.com>
Cc: Linux-mm <linux-mm@kvack.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120330182631.10018.48175.sendpatchset@srdronam.in.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      d4b3b638
  11. 14 3月, 2012 1 次提交
    • S
      uprobes/core: Handle breakpoint and singlestep exceptions · 0326f5a9
      由 Srikar Dronamraju 提交于 
      Uprobes uses exception notifiers to get to know if a thread hit
a breakpoint or a singlestep exception.

When a thread hits a uprobe or is singlestepping post a uprobe
hit, the uprobe exception notifier sets its TIF_UPROBE bit,
which will then be checked on its return to userspace path
(do_notify_resume() ->uprobe_notify_resume()), where the
consumers handlers are run (in task context) based on the
defined filters.

Uprobe hits are thread specific and hence we need to maintain
information about if a task hit a uprobe, what uprobe was hit,
the slot where the original instruction was copied for xol so
that it can be singlestepped with appropriate fixups.

In some cases, special care is needed for instructions that are
executed out of line (xol). These are architecture specific
artefacts, such as handling RIP relative instructions on x86_64.

Since the instruction at which the uprobe was inserted is
executed out of line, architecture specific fixups are added so
that the thread continues normal execution in the presence of a
uprobe.

Postpone the signals until we execute the probed insn.
post_xol() path does a recalc_sigpending() before return to
user-mode, this ensures the signal can't be lost.

Uprobes relies on DIE_DEBUG notification to notify if a
singlestep is complete.

Adds x86 specific uprobe exception notifiers and appropriate
hooks needed to determine a uprobe hit and subsequent post
processing.

Add requisite x86 fixups for xol for uprobes. Specific cases
needing fixups include relative jumps (x86_64), calls, etc.

Where possible, we check and skip singlestepping the
breakpointed instructions. For now we skip single byte as well
as few multibyte nop instructions. However this can be extended
to other instructions too.

Credits to Oleg Nesterov for suggestions/patches related to
signal, breakpoint, singlestep handling code.
Signed-off-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@linux.vnet.ibm.com>
Cc: Linux-mm <linux-mm@kvack.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120313180011.29771.89027.sendpatchset@srdronam.in.ibm.com
[ Performed various cleanliness edits ]
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      0326f5a9
  13. 13 3月, 2012 3 次提交
  15. 22 2月, 2012 4 次提交
  17. 17 2月, 2012 2 次提交
    • I
      uprobes/core: Clean up, refactor and improve the code · 7b2d81d4
      由 Ingo Molnar 提交于 
      Make the uprobes code readable to me:

 - improve the Kconfig text so that a mere mortal gets some idea
   what CONFIG_UPROBES=y is really about

 - do trivial renames to standardize around the uprobes_*() namespace

 - clean up and simplify various code flow details

 - separate basic blocks of functionality

 - line break artifact and white space related removal

 - use standard local varible definition blocks

 - use vertical spacing to make things more readable

 - remove unnecessary volatile

 - restructure comment blocks to make them more uniform and
   more readable in general

Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Anton Arapov <anton@redhat.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Link: http://lkml.kernel.org/n/tip-ewbwhb8o6navvllsauu7k07p@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@elte.hu>
      7b2d81d4
    • S
      uprobes, mm, x86: Add the ability to install and remove uprobes breakpoints · 2b144498
      由 Srikar Dronamraju 提交于 
      Add uprobes support to the core kernel, with x86 support.

This commit adds the kernel facilities, the actual uprobes
user-space ABI and perf probe support comes in later commits.

General design:

Uprobes are maintained in an rb-tree indexed by inode and offset
(the offset here is from the start of the mapping). For a unique
(inode, offset) tuple, there can be at most one uprobe in the
rb-tree.

Since the (inode, offset) tuple identifies a unique uprobe, more
than one user may be interested in the same uprobe. This provides
the ability to connect multiple 'consumers' to the same uprobe.

Each consumer defines a handler and a filter (optional). The
'handler' is run every time the uprobe is hit, if it matches the
'filter' criteria.

The first consumer of a uprobe causes the breakpoint to be
inserted at the specified address and subsequent consumers are
appended to this list.  On subsequent probes, the consumer gets
appended to the existing list of consumers. The breakpoint is
removed when the last consumer unregisters. For all other
unregisterations, the consumer is removed from the list of
consumers.

Given a inode, we get a list of the mms that have mapped the
inode. Do the actual registration if mm maps the page where a
probe needs to be inserted/removed.

We use a temporary list to walk through the vmas that map the
inode.

- The number of maps that map the inode, is not known before we
  walk the rmap and keeps changing.
- extending vm_area_struct wasn't recommended, it's a
  size-critical data structure.
- There can be more than one maps of the inode in the same mm.

We add callbacks to the mmap methods to keep an eye on text vmas
that are of interest to uprobes.  When a vma of interest is mapped,
we insert the breakpoint at the right address.

Uprobe works by replacing the instruction at the address defined
by (inode, offset) with the arch specific breakpoint
instruction. We save a copy of the original instruction at the
uprobed address.

This is needed for:

 a. executing the instruction out-of-line (xol).
 b. instruction analysis for any subsequent fixups.
 c. restoring the instruction back when the uprobe is unregistered.

We insert or delete a breakpoint instruction, and this
breakpoint instruction is assumed to be the smallest instruction
available on the platform. For fixed size instruction platforms
this is trivially true, for variable size instruction platforms
the breakpoint instruction is typically the smallest (often a
single byte).

Writing the instruction is done by COWing the page and changing
the instruction during the copy, this even though most platforms
allow atomic writes of the breakpoint instruction. This also
mirrors the behaviour of a ptrace() memory write to a PRIVATE
file map.

The core worker is derived from KSM's replace_page() logic.

In essence, similar to KSM:

 a. allocate a new page and copy over contents of the page that
    has the uprobed vaddr
 b. modify the copy and insert the breakpoint at the required
    address
 c. switch the original page with the copy containing the
    breakpoint
 d. flush page tables.

replace_page() is being replicated here because of some minor
changes in the type of pages and also because Hugh Dickins had
plans to improve replace_page() for KSM specific work.

Instruction analysis on x86 is based on instruction decoder and
determines if an instruction can be probed and determines the
necessary fixups after singlestep.  Instruction analysis is done
at probe insertion time so that we avoid having to repeat the
same analysis every time a probe is hit.

A lot of code here is due to the improvement/suggestions/inputs
from Peter Zijlstra.

Changelog:

(v10):
 - Add code to clear REX.B prefix as suggested by Denys Vlasenko
   and Masami Hiramatsu.

(v9):
 - Use insn_offset_modrm as suggested by Masami Hiramatsu.

(v7):

 Handle comments from Peter Zijlstra:

 - Dont take reference to inode. (expect inode to uprobe_register to be sane).
 - Use PTR_ERR to set the return value.
 - No need to take reference to inode.
 - use PTR_ERR to return error value.
 - register and uprobe_unregister share code.

(v5):

 - Modified del_consumer as per comments from Peter.
 - Drop reference to inode before dropping reference to uprobe.
 - Use i_size_read(inode) instead of inode->i_size.
 - Ensure uprobe->consumers is NULL, before __uprobe_unregister() is called.
 - Includes errno.h as recommended by Stephen Rothwell to fix a build issue
   on sparc defconfig
 - Remove restrictions while unregistering.
 - Earlier code leaked inode references under some conditions while
   registering/unregistering.
 - Continue the vma-rmap walk even if the intermediate vma doesnt
   meet the requirements.
 - Validate the vma found by find_vma before inserting/removing the
   breakpoint
 - Call del_consumer under mutex_lock.
 - Use hash locks.
 - Handle mremap.
 - Introduce find_least_offset_node() instead of close match logic in
   find_uprobe
 - Uprobes no more depends on MM_OWNER; No reference to task_structs
   while inserting/removing a probe.
 - Uses read_mapping_page instead of grab_cache_page so that the pages
   have valid content.
 - pass NULL to get_user_pages for the task parameter.
 - call SetPageUptodate on the new page allocated in write_opcode.
 - fix leaking a reference to the new page under certain conditions.
 - Include Instruction Decoder if Uprobes gets defined.
 - Remove const attributes for instruction prefix arrays.
 - Uses mm_context to know if the application is 32 bit.
Signed-off-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Also-written-by: NJim Keniston <jkenisto@us.ibm.com>
Reviewed-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Roland McGrath <roland@hack.frob.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Anton Arapov <anton@redhat.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linux-mm <linux-mm@kvack.org>
Link: http://lkml.kernel.org/r/20120209092642.GE16600@linux.vnet.ibm.com
[ Made various small edits to the commit log ]
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      2b144498