[PATCH] preempt: Move PREEMPT_RT before PREEMPT in vermagic.

Since the dynamic preemption has been enabled for PREEMPT_RT we have now
CONFIG_PREEMPT and CONFIG_PREEMPT_RT set simultaneously. This affects
the vermagic strings which comes now PREEMPT with PREEMPT_RT enabled.

The PREEMPT_RT module usually can not be loaded on a PREEMPT kernel
because some symbols are missing.
However if the symbols are fine then it continues and it crashes later.
The problem is that the struct module has a different layout and the
num_exentries or init members are at a different position leading to a
crash later on. This is not necessary caught by the size check in
elf_validity_cache_index_mod() because the mem member has an alignment
requirement of __module_memory_align which is big enough keep the total
size unchanged. Therefore we should keep the string accurate instead of
removing it.

Move the PREEMPT_RT check before the PREEMPT so that it takes precedence
if both symbols are enabled.

Fixes: 35772d627b55c ("sched: Enable PREEMPT_DYNAMIC for PREEMPT_RT")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/vermagic.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/vermagic.h b/include/linux/vermagic.h
index a54046bf37e55..939ceabcaf06f 100644
--- a/include/linux/vermagic.h
+++ b/include/linux/vermagic.h

@@ -15,10 +15,10 @@
 #else
 #define MODULE_VERMAGIC_SMP ""
 #endif
-#ifdef CONFIG_PREEMPT_BUILD
-#define MODULE_VERMAGIC_PREEMPT "preempt "
-#elif defined(CONFIG_PREEMPT_RT)
+#ifdef CONFIG_PREEMPT_RT
 #define MODULE_VERMAGIC_PREEMPT "preempt_rt "
+#elif defined(CONFIG_PREEMPT_BUILD)
+#define MODULE_VERMAGIC_PREEMPT "preempt "
 #else
 #define MODULE_VERMAGIC_PREEMPT ""
 #endif

-- 
2.45.2

On 12/5/24 17:06, Sebastian Andrzej Siewior wrote:

Since the dynamic preemption has been enabled for PREEMPT_RT we have now
CONFIG_PREEMPT and CONFIG_PREEMPT_RT set simultaneously. This affects
the vermagic strings which comes now PREEMPT with PREEMPT_RT enabled.

The PREEMPT_RT module usually can not be loaded on a PREEMPT kernel
because some symbols are missing.
However if the symbols are fine then it continues and it crashes later.
The problem is that the struct module has a different layout and the
num_exentries or init members are at a different position leading to a
crash later on. This is not necessary caught by the size check in
elf_validity_cache_index_mod() because the mem member has an alignment
requirement of __module_memory_align which is big enough keep the total
size unchanged. Therefore we should keep the string accurate instead of
removing it.

Move the PREEMPT_RT check before the PREEMPT so that it takes precedence
if both symbols are enabled.

Fixes: 35772d627b55c ("sched: Enable PREEMPT_DYNAMIC for PREEMPT_RT")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>

I'm going to wait for a few days if others want to comment and then plan
to take this through the modules tree for 6.13-rcX fixes.

[Luis asked me to look after the modules tree for a while, with the plan
to rotate it.]

-- 
Thanks,
Petr

On 2024-12-10 14:52:23 [+0100], Petr Pavlu wrote:

Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>

I'm going to wait for a few days if others want to comment and then plan
to take this through the modules tree for 6.13-rcX fixes.

thank you.

[Luis asked me to look after the modules tree for a while, with the plan
to rotate it.]

understood.

Sebastian