| Age | Commit message (Collapse) | Author |
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If filter_add_subsystem_pred() fails due to ENOSPC or ENOMEM,
the pred doesn't get freed, while as a side effect it does for
other errors. Make it so the caller always frees the pred for
any error.
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <1249746593.6453.32.camel@tropicana>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Dan Carpenter sent me a fix to prevent pred from being used if
it couldn't be allocated. I noticed the same problem also
existed for the create_pred() case and added a fix for that.
Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <1249746549.6453.29.camel@tropicana>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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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: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A375A4D.6000205@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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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: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A375A30.9060802@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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I forgot to update filter code accordingly in
"tracing/events: change the type of __str_loc_item to unsigned short"
(commt b0aae68cc5508f3c2fbf728988c954db4c8b8a53)
It can cause system crash:
# echo 1 > tracing/events/irq/irq_handler_entry/enable
# echo 'name == eth0' > tracing/events/irq/irq_handler_entry/filter
[ Impact: fix crash while filtering on __string() field ]
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A35B905.3090500@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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This should be a bug:
# cat format
name: foo_bar
ID: 71
format:
...
field:int bar; offset:24; size:4;
# echo 'bar < 0' > filter
# echo 'bar < -1' > filter
bash: echo: write error: Invalid argument
[ Impact: fix to allow negative operand in filer expr ]
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A35B8DF.60400@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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__string() is limited:
- it's a char array, but we may want to define array with other types
- a source string should be available, but we may just know the string size
We introduce __dynamic_array() to break those limitations, and __string()
becomes a wrapper of it. As a side effect, now __get_str() can be used
in TP_fast_assign but not only TP_print.
Take XFS for example, we have the string length in the dirent, but the
string itself is not NULL-terminated, so __dynamic_array() can be used:
TRACE_EVENT(xfs_dir2,
TP_PROTO(struct xfs_da_args *args),
TP_ARGS(args),
TP_STRUCT__entry(
__field(int, namelen)
__dynamic_array(char, name, args->namelen + 1)
...
),
TP_fast_assign(
char *name = __get_str(name);
if (args->namelen)
memcpy(name, args->name, args->namelen);
name[args->namelen] = '\0';
__entry->namelen = args->namelen;
),
TP_printk("name %.*s namelen %d",
__entry->namelen ? __get_str(name) : NULL
__entry->namelen)
);
[ Impact: allow defining dynamic size arrays ]
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A2384D2.3080403@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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We should leave the last slot for the ending '\0'.
[ Impact: fix possible crash when the length of an operand is 128 ]
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A0CDC8C.30602@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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[ Impact: fix deadlock in a rare case we fail to allocate memory ]
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4A0CDC6F.7070200@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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In filter_add_subsystem_pred() we should release event_mutex before
calling filter_free_subsystem_preds(), since both functions hold
event_mutex.
[ Impact: fix deadlock when writing invalid pred into subsystem filter ]
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: tzanussi@gmail.com
Cc: a.p.zijlstra@chello.nl
Cc: fweisbec@gmail.com
Cc: rostedt@goodmis.org
LKML-Reference: <4A028993.7020509@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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When we set a filter for an event, such as:
echo "name == my_lock_name" > \
/debug/tracing/events/lockdep/lock_acquired/filter
then the following order of token type is parsed:
- space
- operator
- parentheses
- operand
Because the operators and parentheses have a higher precedence
than the operand characters, which is normal, then we can't
use any string containing such special characters:
()=<>!&|
To get this support and also avoid ambiguous intepretation from
the parser or the human, we can do it using double quotes so that
we keep the usual languages habits.
Then after this patch you can still declare string condition like
before:
echo name == myname
But if you want to compare against a string containing an operator
character, you can use double quotes:
echo 'name == "&myname"'
Don't forget to include the whole expression into single quotes or
the double ones will be eaten by echo.
[ Impact: support strings with special characters for tracing filters ]
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Zhaolei <zhaolei@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
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Currently the filtering infrastructure supports well the
numeric types and fixed sized array types.
But the recently added __string() field uses a specific
indirect offset mechanism which requires a specific
predicate. Until now it wasn't supported.
This patch adds this support and implies very few changes,
only a new predicate is needed, the management of this specific
field can be done through the usual string helpers in the
filtering infrastructure.
[ Impact: support all kinds of strings in the tracing filters ]
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Zhaolei <zhaolei@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
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A module will add/remove its trace events when it gets loaded/unloaded, so
the ftrace_events list is not "const", and concurrent access needs to be
protected.
This patch thus fixes races between loading/unloding modules and read
'available_events' or read/write 'set_event', etc.
Below shows how to reproduce the race:
# for ((; ;)) { cat /mnt/tracing/available_events; } > /dev/null &
# for ((; ;)) { insmod trace-events-sample.ko; rmmod sample; } &
After a while:
BUG: unable to handle kernel paging request at 0010011c
IP: [<c1080f27>] t_next+0x1b/0x2d
...
Call Trace:
[<c10c90e6>] ? seq_read+0x217/0x30d
[<c10c8ecf>] ? seq_read+0x0/0x30d
[<c10b4c19>] ? vfs_read+0x8f/0x136
[<c10b4fc3>] ? sys_read+0x40/0x65
[<c1002a68>] ? sysenter_do_call+0x12/0x36
[ Impact: fix races when concurrent accessing ftrace_events list ]
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <4A00F709.3080800@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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When unloading a module, memory allocated by init_preds() and
trace_define_field() is not freed.
[ Impact: fix memory leak ]
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <4A00F6E0.3040503@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Replace the current event parser hack with a better one. Filters are
no longer specified predicate by predicate, but all at once and can
use parens and any of the following operators:
numeric fields:
==, !=, <, <=, >, >=
string fields:
==, !=
predicates can be combined with the logical operators:
&&, ||
examples:
"common_preempt_count > 4" > filter
"((sig >= 10 && sig < 15) || sig == 17) && comm != bash" > filter
If there was an error, the erroneous string along with an error
message can be seen by looking at the filter e.g.:
((sig >= 10 && sig < 15) || dsig == 17) && comm != bash
^
parse_error: Field not found
Currently the caret for an error always appears at the beginning of
the filter; a real position should be used, but the error message
should be useful even without it.
To clear a filter, '0' can be written to the filter file.
Filters can also be set or cleared for a complete subsystem by writing
the same filter as would be written to an individual event to the
filter file at the root of the subsytem. Note however, that if any
event in the subsystem lacks a field specified in the filter being
set, the set will fail and all filters in the subsytem are
automatically cleared. This change from the previous version was made
because using only the fields that happen to exist for a given event
would most likely result in a meaningless filter.
Because the logical operators are now implemented as predicates, the
maximum number of predicates in a filter was increased from 8 to 16.
[ Impact: add new, extended trace-filter implementation ]
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: fweisbec@gmail.com
Cc: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <1240905899.6416.121.camel@tropicana>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Create a new event_filter object, and move the pred-related members
out of the call and subsystem objects and into the filter object - the
details of the filter implementation don't need to be exposed in the
call and subsystem in any case, and it will also help make the new
parser implementation a little cleaner.
[ Impact: refactor trace-filter code to prepare for new features ]
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: fweisbec@gmail.com
Cc: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <1240905887.6416.119.camel@tropicana>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Suppose we would like to trace all tasks named '123', but this
will fail:
# echo 'parent_comm == 123' > events/sched/sched_process_fork/filter
bash: echo: write error: Invalid argument
Don't guess the type of the filter pred in filter_parse(), but instead
we check it in __filter_add_pred().
[ Impact: extend allowed filter field string values ]
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <49ED8DEB.6000700@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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This patch adds a filter_mutex to prevent the filter predicates from
being accessed concurrently by various external functions.
It's based on a previous patch by Li Zefan:
"[PATCH 7/7] tracing/filters: make filter preds RCU safe"
v2 changes:
- fixed wrong value returned in a add_subsystem_pred() failure case
noticed by Li Zefan.
[ Impact: fix trace filter corruption/crashes on parallel access ]
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Tested-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: paulmck@linux.vnet.ibm.com
LKML-Reference: <1239946028.6639.13.camel@tropicana>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Impact: let modules add trace events
The trace event code requires some functions to be exported to allow
modules to use TRACE_EVENT. This patch adds EXPORT_SYMBOL_GPL to the
necessary functions.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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Impact: makes it possible to define events in modules
The events are created by reading down the section that they are linked
in by the macros. But this is not scalable to modules. This patch converts
the manipulations to use a global link list, and on boot up it adds
the items in the section to the list.
This change will allow modules to add their tracing events to the list as
well.
Note, this change alone does not permit modules to use the TRACE_EVENT macros,
but the change is needed for them to eventually do so.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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This patch allows event filters to be safely removed or switched
on-the-fly while avoiding the use of rcu or the suspension of tracing of
previous versions.
It does it by adding a new filter_pred_none() predicate function which
does nothing and by never deallocating either the predicates or any of
the filter_pred members used in matching; the predicate lists are
allocated and initialized during ftrace_event_calls initialization.
Whenever a filter is removed or replaced, the filter_pred_* functions
currently in use by the affected ftrace_event_call are immediately
switched over to to the filter_pred_none() function, while the rest of
the filter_pred members are left intact, allowing any currently
executing filter_pred_* functions to finish up, using the values they're
currently using.
In the case of filter replacement, the new predicate values are copied
into the old predicates after the above step, and the filter_pred_none()
functions are replaced by the filter_pred_* functions for the new
filter. In this case, it is possible though very unlikely that a
previous filter_pred_* is still running even after the
filter_pred_none() switch and the switch to the new filter_pred_*. In
that case, however, because nothing has been deallocated in the
filter_pred, the worst that can happen is that the old filter_pred_*
function sees the new values and as a result produces either a false
positive or a false negative, depending on the values it finds.
So one downside to this method is that rarely, it can produce a bad
match during the filter switch, but it should be possible to live with
that, IMHO.
The other downside is that at least in this patch the predicate lists
are always pre-allocated, taking up memory from the start. They could
probably be allocated on first-use, and de-allocated when tracing is
completely stopped - if this patch makes sense, I could create another
one to do that later on.
Oh, and it also places a restriction on the size of __arrays in events,
currently set to 128, since they can't be larger than the now embedded
str_val arrays in the filter_pred struct.
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: paulmck@linux.vnet.ibm.com
LKML-Reference: <1239610670.6660.49.camel@tropicana>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Merge reason: merge latest tracing fixes to avoid conflicts in
kernel/trace/trace_events_filter.c with upcoming change
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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This patch adds run-time field descriptions to all the event formats
exported using TRACE_EVENT_FORMAT. It also hooks up all the tracers
that use them (i.e. the tracers in the 'ftrace subsystem') so they can
also have their output filtered by the event-filtering mechanism.
When I was testing this, there were a couple of things that fooled me
into thinking the filters weren't working, when actually they were -
I'll mention them here so others don't make the same mistakes (and file
bug reports. ;-)
One is that some of the tracers trace multiple events e.g. the
sched_switch tracer uses the context_switch and wakeup events, and if
you don't set filters on all of the traced events, the unfiltered output
from the events without filters on them can make it look like the
filtering as a whole isn't working properly, when actually it is doing
what it was asked to do - it just wasn't asked to do the right thing.
The other is that for the really high-volume tracers e.g. the function
tracer, the volume of filtered events can be so high that it pushes the
unfiltered events out of the ring buffer before they can be read so e.g.
cat'ing the trace file repeatedly shows either no output, or once in
awhile some output but that isn't there the next time you read the
trace, which isn't what you normally expect when reading the trace file.
If you read from the trace_pipe file though, you can catch them before
they disappear.
Changes from v1:
As suggested by Frederic Weisbecker:
- get rid of externs in functions
- added unlikely() to filter_check_discard()
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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- propagate return value of filter_add_pred() to the user
- return -ENOSPC but not -ENOMEM or -EINVAL when the filter array
is full
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Tom Zanussi <tzanussi@gmail.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <49E04CF0.3010105@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Before patch:
# echo 'parent_pid == 0x10' > events/sched/sched_process_fork/filter
# cat sched/sched_process_fork/filter
parent_pid == 0
After patch:
# cat sched/sched_process_fork/filter
parent_pid == 16
Also check the input more strictly.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Tom Zanussi <tzanussi@gmail.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <49E04C53.4010600@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Try this, and you'll see NULL pointer dereference bug:
# echo -n 'parent_comm ==' > sched/sched_process_fork/filter
Because we passed NULL ptr to simple_strtoull().
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Tom Zanussi <tzanussi@gmail.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <49E04C43.1050504@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Impact: fix filter use boundary condition / crash
Make sure filters for string fields don't use integer values and vice
versa. Getting it wrong can crash the system or produce bogus
results.
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: =?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1237878882.8339.61.camel@charm-linux>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Impact: cleanup
Instead of just using the trace_seq buffer to print the filters, use
trace_seq_printf() as it was intended to be used.
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: =?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1237878871.8339.59.camel@charm-linux>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Impact: cleanup
No need to use the safe version here, so use list_for_each_entry instead
of list_for_each_entry_safe in find_event_field().
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: =?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1237878841.8339.57.camel@charm-linux>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Impact: cleanup, memory leak fix
This patch cleans up filter_add_subsystem_pred():
- searches for the field before creating a copy of the pred
- fixes memory leak in the case a predicate isn't applied
- if -ENOMEM, makes sure there's no longer a reference to the
pred so the caller can free the half-finished filter
- changes the confusing i == MAX_FILTER_PRED - 1 comparison
previously remarked upon
This affects only per-subsystem event filtering.
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: =?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1237796808.7527.40.camel@charm-linux>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Impact: fix potential crash on subsystem filter expression freeing
When making a copy of the predicate, pred->field_name needs to be
duplicated in the copy as well, otherwise bad things can happen due to
later multiple frees of the same string.
This affects only per-subsystem event filtering.
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: =?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1237796802.7527.39.camel@charm-linux>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Impact: cleanup
Use list_for_each_entry_safe instead of list_for_each_entry in
find_event_field().
Reported-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <1237796788.7527.35.camel@charm-linux>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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This patch adds per-subsystem filtering to the event tracing subsystem.
It adds a 'filter' debugfs file to each subsystem directory. This file
can be written to to set filters; reading from it will display the
current set of filters set for that subsystem.
Basically what it does is propagate the filter down to each event
contained in the subsystem. If a particular event doesn't have a field
with the name specified in the filter, it simply doesn't get set for
that event. You can verify whether or not the filter was set for a
particular event by looking at the filter file for that event.
As with per-event filters, compound expressions are supported, echoing
'0' to the subsystem's filter file clears all filters in the subsystem,
etc.
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1237710677.7703.49.camel@charm-linux>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
|
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This patch adds per-event filtering to the event tracing subsystem.
It adds a 'filter' debugfs file to each event directory. This file can
be written to to set filters; reading from it will display the current
set of filters set for that event.
Basically, any field listed in the 'format' file for an event can be
filtered on (including strings, but not yet other array types) using
either matching ('==') or non-matching ('!=') 'predicates'. A
'predicate' can be either a single expression:
# echo pid != 0 > filter
# cat filter
pid != 0
or a compound expression of up to 8 sub-expressions combined using '&&'
or '||':
# echo comm == Xorg > filter
# echo "&& sig != 29" > filter
# cat filter
comm == Xorg
&& sig != 29
Only events having field values matching an expression will be available
in the trace output; non-matching events are discarded.
Note that a compound expression is built up by echoing each
sub-expression separately - it's not the most efficient way to do
things, but it keeps the parser simple and assumes that compound
expressions will be relatively uncommon. In any case, a subsequent
patch introducing a way to set filters for entire subsystems should
mitigate any need to do this for lots of events.
Setting a filter without an '&&' or '||' clears the previous filter
completely and sets the filter to the new expression:
# cat filter
comm == Xorg
&& sig != 29
# echo comm != Xorg
# cat filter
comm != Xorg
To clear a filter, echo 0 to the filter file:
# echo 0 > filter
# cat filter
none
The limit of 8 predicates for a compound expression is arbitrary - for
efficiency, it's implemented as an array of pointers to predicates, and
8 seemed more than enough for any filter...
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1237710665.7703.48.camel@charm-linux>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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