ping! Currently "perf record -e [tracepoint]" is unusable if AFS is builtin. On Fri, May 28, 2021 at 01:04:46AM +0300, Alexey Dobriyan wrote: > I was adding custom tracepoint to the kernel, grabbed full F34 kernel > .config, disabled modules and booted whole shebang as VM kernel. > > Then did > > perf record -a -e ... > > It crashed: > > general protection fault, probably for non-canonical address 0x435f5346592e4243: 0000 [#1] SMP PTI > CPU: 1 PID: 842 Comm: cat Not tainted 5.12.6+ #26 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1.fc33 04/01/2014 > RIP: 0010:t_show+0x22/0xd0 > > Then reproducer was narrowed to > > # cat /sys/kernel/tracing/printk_formats > > Original F34 kernel with modules didn't crash. > > So I started to disable options and after disabling AFS everything > started working again. > > The root cause is that AFS was placing char arrays content into a section > full of _pointers_ to strings with predictable consequences. > > Non canonical address 435f5346592e4243 is "CB.YFS_" which came from > CM_NAME macro. > > The fix is to create char array and pointer to it separatedly. > > Steps to reproduce: > > CONFIG_AFS=y > CONFIG_TRACING=y > > # cat /sys/kernel/tracing/printk_formats > > Signed-off-by: Alexey Dobriyan (SK hynix) <adobriyan@xxxxxxxxx> > --- > > fs/afs/cmservice.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > --- a/fs/afs/cmservice.c > +++ b/fs/afs/cmservice.c > @@ -30,8 +30,9 @@ static void SRXAFSCB_TellMeAboutYourself(struct work_struct *); > static int afs_deliver_yfs_cb_callback(struct afs_call *); > > #define CM_NAME(name) \ > - char afs_SRXCB##name##_name[] __tracepoint_string = \ > - "CB." #name > + const char afs_SRXCB##name##_name[] = "CB." #name; \ > + static const char *_afs_SRXCB##name##_name __tracepoint_string =\ > + afs_SRXCB##name##_name > > /* > * CB.CallBack operation type
