On Fri, 18 Mar 2022 19:34:32 +0000, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx> > > When an enum is used in the visible parts of a trace event that is > exported to user space, the user space applications like perf and > trace-cmd do not have a way to know what the value of the enum is. To > solve this, at boot up (or module load) the printk formats are modified to > replace the enum with their numeric value in the string output. > > Array fields of the event are defined by [<nr-elements>] in the type > portion of the format file so that the user space parsers can correctly > parse the array into the appropriate size chunks. But in some trace > events, an enum is used in defining the size of the array, which once > again breaks the parsing of user space tooling. > > This was solved the same way as the print formats were, but it modified > the type strings of the trace event. This caused crashes in some > architectures because, as supposed to the print string, is a const string > value. This was not detected on x86, as it appears that const strings are > still writable (at least in boot up), but other architectures this is not > the case, and writing to a const string will cause a kernel fault. > > To fix this, use kstrdup() to copy the type before modifying it. If the > trace event is for the core kernel there's no need to free it because the > string will be in use for the life of the machine being on line. For > modules, create a link list to store all the strings being allocated for > modules and when the module is removed, free them. > > Link: https://lore.kernel.org/all/yt9dr1706b4i.fsf@xxxxxxxxxxxxx/ > > Fixes: b3bc8547d3be ("tracing: Have TRACE_DEFINE_ENUM affect trace event types as well") > Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx> This fixes booting on arm64 with ext4 as a module, so FWIW: Tested-by: Marc Zyngier <maz@xxxxxxxxxx> M. -- Without deviation from the norm, progress is not possible.
