Ensure you keep the extracted patch file, patch-5.4.69-rt39.patch, in the directory immediately above the 5.4.69 kernel source tree (as seen previously). Now, let's apply the patch. Careful – (obviously) don't attempt to apply the compressed file as the patch; extract and use the uncompressed patch file. To ensure that the patch applies correctly, we first employ the --dry-run (dummy run) option to patch(1):
$ cd linux-5.4.69
$ patch -p1 --dry-run < ../patch-5.4.69-rt39.patch
checking file Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.html
checking file Documentation/RCU/Design/Requirements/Requirements.html
[ ... ]
checking file virt/kvm/arm/arm.c
$ echo $?
0
All's well, let's now actually apply it:
$ patch -p1 < ../patch-5.4.69-rt39.patch
patching file Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.html
patching file Documentation/RCU/Design/Requirements/Requirements...
