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  1. 18 Jun, 2009 1 commit
    • Steven Rostedt's avatar
      function-graph: disable when both x86_32 and optimize for size are configured · eb4a0378
      Steven Rostedt authored 
      On x86_32, when optimize for size is set, gcc may align the frame pointer
and make a copy of the the return address inside the stack frame.
The return address that is located in the stack frame may not be
the one used to return to the calling function. This will break the
function graph tracer.

The function graph tracer replaces the return address with a jump to a hook
function that can trace the exit of the function. If it only replaces
a copy, then the hook will not be called when the function returns.
Worse yet, when the parent function returns, the function graph tracer
will return back to the location of the child function which will
easily crash the kernel with weird results.

To see the problem, when i386 is compiled with -Os we get:

c106be03:       57                      push   %edi
c106be04:       8d 7c 24 08             lea    0x8(%esp),%edi
c106be08:       83 e4 e0                and    $0xffffffe0,%esp
c106be0b:       ff 77 fc                pushl  0xfffffffc(%edi)
c106be0e:       55                      push   %ebp
c106be0f:       89 e5                   mov    %esp,%ebp
c106be11:       57                      push   %edi
c106be12:       56                      push   %esi
c106be13:       53                      push   %ebx
c106be14:       81 ec 8c 00 00 00       sub    $0x8c,%esp
c106be1a:       e8 f5 57 fb ff          call   c1021614 <mcount>

When it is compiled with -O2 instead we get:

c10896f0:       55                      push   %ebp
c10896f1:       89 e5                   mov    %esp,%ebp
c10896f3:       83 ec 28                sub    $0x28,%esp
c10896f6:       89 5d f4                mov    %ebx,0xfffffff4(%ebp)
c10896f9:       89 75 f8                mov    %esi,0xfffffff8(%ebp)
c10896fc:       89 7d fc                mov    %edi,0xfffffffc(%ebp)
c10896ff:       e8 d0 08 fa ff          call   c1029fd4 <mcount>

The compile with -Os will align the stack pointer then set up the
frame pointer (%ebp), and it copies the return address back into
the stack frame. The change to the return address in mcount is done
to the copy and not the real place holder of the return address.

Then compile with -O2 sets up the frame pointer first, this makes
the change to the return address by mcount affect where the function
will jump on exit.
Reported-by: default avatarJake Edge <jake@lwn.net>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      eb4a0378
  3. 17 Jun, 2009 7 commits
    • Steven Rostedt's avatar
      ring-buffer: have benchmark test print to trace buffer · 4b221f03
      Steven Rostedt authored 
      Currently the output of the ring buffer benchmark/test prints to
the console. This test runs for ten seconds every ten seconds and
ouputs the result after every iteration. This needlessly fills up
the logs.

This patch makes the ring buffer benchmark/test print to the ftrace
buffer using trace_printk. To view the test results, you must examine
the debug/tracing/trace file.
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      4b221f03
    • Steven Rostedt's avatar
      ring-buffer: do not grab locks in nmi · 8d707e8e
      Steven Rostedt authored 
      If ftrace_dump_on_oops is set, and an NMI detects a lockup, then it
will need to read from the ring buffer. But the read side of the
ring buffer still takes locks. This patch adds a check on the read
side that if it is in an NMI, then it will disable the ring buffer
and not take any locks.

Reads can still happen on a disabled ring buffer.
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      8d707e8e
    • Steven Rostedt's avatar
      ring-buffer: add locks around rb_per_cpu_empty · d4788207
      Steven Rostedt authored 
      The checking of whether the buffer is empty or not needs to be serialized
among the readers. Add the reader spin lock around it.
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      d4788207
    • Steven Rostedt's avatar
      ring-buffer: check for less than two in size allocation · 5f78abee
      Steven Rostedt authored 
      The ring buffer must have at least two pages allocated for the
reader page swap to work.

The page count check will miss the case of a zero size passed in.
Even though a zero size ring buffer would probably fail an allocation,
making the min size check for less than two instead of equal to one makes
the code a bit more robust.
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      5f78abee
    • Steven Rostedt's avatar
      ring-buffer: remove useless compile check for buffer_page size · 0dcd4d6c
      Steven Rostedt authored 
      The original version of the ring buffer had a hack to map the
page struct that held the pages of the buffer to also be the structure
that the ring buffer would keep the pages in a link list.

This overlap of the page struct was very dangerous and that hack was
removed a while ago.

But there was a check to make sure the buffer_page never became bigger
than the page struct, and would fail the compile if it did. The
check was only meaningful when we had the hack. Now that we have separate
allocated descriptors for the buffer pages, we can remove this check.
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      0dcd4d6c
    • Steven Rostedt's avatar
      ring-buffer: remove useless warn on check · c6a9d7b5
      Steven Rostedt authored 
      A check if "write > BUF_PAGE_SIZE" is done right after a

	if (write > BUF_PAGE_SIZE)
		return ...;

Thus the check is actually testing the compiler and not the
kernel. This is useless, remove it.
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      c6a9d7b5
    • Steven Rostedt's avatar
      ring-buffer: use BUF_PAGE_HDR_SIZE in calculating index · 22f470f8
      Steven Rostedt authored 
      The index of the event is found by masking PAGE_MASK to it and
subtracting the header size. Currently the header size is calculate
by PAGE_SIZE - BUF_PAGE_SIZE, when we already have a macro
BUF_PAGE_HDR_SIZE to define it.

If we want to change BUF_PAGE_SIZE to something less than filling
the rest of the page (this is done for debugging), then we break
the algorithm to find the index.
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      22f470f8
  5. 16 Jun, 2009 6 commits
    • Steven Rostedt's avatar
      tracing: update sample event documentation · 44ad18e0
      Steven Rostedt authored 
      The comments in the sample code is a bit confusing. This patch
cleans them up a little.
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      44ad18e0
    • Li Zefan's avatar
      tracing/filters: fix race between filter setting and module unload · 00e95830
      Li Zefan authored 
      Module unload is protected by event_mutex, while setting filter is
protected by filter_mutex. This leads to the race:

echo 'bar == 0 || bar == 10' \    |
		> sample/filter   |
                                  |  insmod sample.ko
  add_pred("bar == 0")            |
    -> n_preds == 1               |
  add_pred("bar == 100")          |
    -> n_preds == 2               |
                                  |  rmmod sample.ko
                                  |  insmod sample.ko
  add_pred("&&")                  |
    -> n_preds == 1 (should be 3) |

Now event->filter->preds is corrupted. An then when filter_match_preds()
is called, the WARN_ON() in it will be triggered.

To avoid the race, we remove filter_mutex, and replace it with event_mutex.

[ Impact: prevent corruption of filters by module removing and loading ]
Signed-off-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A375A4D.6000205@cn.fujitsu.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      00e95830
    • Li Zefan's avatar
      tracing/filters: free filter_string in destroy_preds() · 57be8887
      Li Zefan authored 
      filter->filter_string is not freed when unloading a module:

 # insmod trace-events-sample.ko
 # echo "bar < 100" > /mnt/tracing/events/sample/foo_bar/filter
 # rmmod trace-events-sample.ko

[ Impact: fix memory leak when unloading module ]
Signed-off-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A375A30.9060802@cn.fujitsu.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      57be8887
    • Steven Rostedt's avatar
      ring-buffer: use commit counters for commit pointer accounting · fa743953
      Steven Rostedt authored 
      The ring buffer is made up of three sets of pointers.

The head page pointer, which points to the next page for the reader to
get.

The commit pointer and commit index, which points to the page and index
of the last committed write respectively.

The tail pointer and tail index, which points to the page and the index
of the last reserved data respectively (non committed).

The commit pointer is only moved forward by the outer most writer.
If a nested writer comes in, it will not move the pointer forward.

The current implementation has a flaw. It assumes that the outer most
writer successfully reserved data. There's a small race window where
the outer most writer could find the tail pointer, but a nested
writer could come in (via interrupt) and move the tail forward, and
even the commit forward.

The outer writer would not realized the commit moved forward and the
accounting will break.

This patch changes the design to use counters in the per cpu buffers
to keep track of commits. The counters are incremented at the start
of the commit, and decremented at the end. If the end commit counter
is 1, then it moves the commit pointers. A loop is made to check for
races between checking and moving the commit pointers. Only the outer
commit should move the pointers anyway.

The test of knowing if a reserve is equal to the last commit update
is still needed to know for time keeping. The time code is much less
racey than the commit updates.

This change not only solves the mentioned race, but also makes the
code simpler.

[ Impact: fix commit race and simplify code ]
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      fa743953
    • Steven Rostedt's avatar
      ring-buffer: remove unused variable · 263294f3
      Steven Rostedt authored 
      Fix the compiler error:

kernel/trace/ring_buffer.c: In function 'rb_move_tail':
kernel/trace/ring_buffer.c:1236: warning: unused variable 'event'
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      263294f3
    • Steven Rostedt's avatar
      ring-buffer: have benchmark test handle discarded events · 9086c7b9
      Steven Rostedt authored 
      With the addition of commit:

  c7b09308
  ring-buffer: prevent adding write in discarded area

The ring buffer may now add discarded events when a write passes
the end of a buffer page. Before, a discarded event was only added
when the tracer deliberately created one. The ring buffer benchmark
test does not handle discarded events when it reads the buffer and
fails when it encounters one.

Also fix the increment for large data entries (luckily, the test did
not add any yet).

[ Impact: fix false failure of ring buffer self test ]
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      9086c7b9
  7. 15 Jun, 2009 7 commits
  9. 14 Jun, 2009 19 commits