Nathan Lynch via B4 Relay <devnull+nathanl.linux.ibm....@kernel.org> writes:
> From: Nathan Lynch <nath...@linux.ibm.com> > > Enabling any of the powerpc:rtas_* tracepoints at boot is likely to > result in an oops on RTAS platforms. For example, booting a QEMU > pseries model with 'trace_event=powerpc:rtas_input' in the command > line leads to: > > BUG: Kernel NULL pointer dereference on read at 0x00000008 > Oops: Kernel access of bad area, sig: 7 [#1] > NIP [c00000000004231c] do_enter_rtas+0x1bc/0x460 > LR [c00000000004231c] do_enter_rtas+0x1bc/0x460 > Call Trace: > do_enter_rtas+0x1bc/0x460 (unreliable) > rtas_call+0x22c/0x4a0 > rtas_get_boot_time+0x80/0x14c > read_persistent_clock64+0x124/0x150 > read_persistent_wall_and_boot_offset+0x28/0x58 > timekeeping_init+0x70/0x348 > start_kernel+0xa0c/0xc1c > start_here_common+0x1c/0x20 > > (This is preceded by a warning for the failed lookup in > rtas_token_to_function().) > > This happens when __do_enter_rtas_trace() attempts a token to function > descriptor lookup before the xarray containing the mappings has been > set up. > > Fall back to linear scan of the table if rtas_token_to_function_xarray > is empty. > Reviewed-by: Aneesh Kumar K.V (IBM) <aneesh.ku...@kernel.org> > Signed-off-by: Nathan Lynch <nath...@linux.ibm.com> > Fixes: 24098f580e2b ("powerpc/rtas: add tracepoints around RTAS entry") > --- > arch/powerpc/kernel/rtas.c | 18 ++++++++++++++---- > 1 file changed, 14 insertions(+), 4 deletions(-) > > diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c > index 1ad1869e2e96..f0051881348a 100644 > --- a/arch/powerpc/kernel/rtas.c > +++ b/arch/powerpc/kernel/rtas.c > @@ -557,11 +557,21 @@ static const struct rtas_function > *rtas_token_to_function(s32 token) > return NULL; > > func = xa_load(&rtas_token_to_function_xarray, token); > + if (func) > + return func; > + /* > + * Fall back to linear scan in case the reverse mapping hasn't > + * been initialized yet. > + */ > + if (xa_empty(&rtas_token_to_function_xarray)) { > + for_each_rtas_function(func) { > + if (func->token == token) > + return func; > + } > + } > > - if (WARN_ONCE(!func, "unexpected failed lookup for token %d", token)) > - return NULL; > - > - return func; > + WARN_ONCE(true, "unexpected failed lookup for token %d", token); > + return NULL; > } > > /* This is here deliberately so it's only used in this file */ > > -- > 2.41.0