Messages in this thread | | | Date | Mon, 03 Aug 2009 14:58:15 +0800 | From | Li Zefan <> | Subject | Re: [RFC][PATCH 5/5] tracing/filters: Provide support for char * pointers |
| |
Frederic Weisbecker wrote: > Provide support for char * pointers in the filtering framework. > Usually, char * entries are dangerous in traces because the string > can be released whereas a pointer to it can still wait to be read from > the ring buffer. But sometimes we can assume it's safe, like in case > of RO data (eg: __file__ or __line__, used in bkl trace event). If > these RO data are in a module and so is the call to the trace event, > then it's safe, because the ring buffer will be flushed once this > module get unloaded. >
The problem is we don't distinguish dangerous char * from safe char *... They are both defined as: __field(char *, str)
So for those dangerous ones, a string filter still can be applied, which will dereference those pointers.
> Now the bkl events becomes more useful. Say that you want to trace > only the bkl use in reiserfs: > > cd /debug/tracing/events/bkl/lock_kernel > echo "file == fs/reiserfs*" > filter_regex > cat /debug/tracing/trace > > syslogd-3658 [001] 1874.661878: lock_kernel: depth: 1, fs/reiserfs/super.c:563 reiserfs_dirty_inode() > syslogd-3658 [001] 1874.662266: lock_kernel: depth: 0, fs/reiserfs/inode.c:2695 reiserfs_write_end() > syslogd-3658 [001] 1874.662268: lock_kernel: depth: 1, fs/reiserfs/super.c:563 reiserfs_dirty_inode() > syslogd-3658 [001] 1874.662291: lock_kernel: depth: 0, fs/reiserfs/inode.c:2695 reiserfs_write_end()
| |