Messages in this thread | | | Date | Thu, 6 Aug 2009 01:02:59 +0200 | From | Frederic Weisbecker <> | Subject | Re: [RFC][PATCH 5/5] tracing/filters: Provide support for char * pointers |
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On Mon, Aug 03, 2009 at 02:58:15PM +0800, Li Zefan wrote: > 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.
Yeah, but only reviewing can distinguish them. It depends on the context. IMO, a __builtin_constant check would be wrong. I don't remember who posted recently tracepoints with char * types that were safe although he didn't use string constants.
> > 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()
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