285a54efe3
ftracetest multiple_kprobes.tc testcase hits the following NULL pointer exception: BUG: kernel NULL pointer dereference, address: 0000000000000000 PGD 800000007bf60067 P4D 800000007bf60067 PUD 7bf5f067 PMD 0 Oops: 0000 [#1] PREEMPT SMP PTI RIP: 0010:poke_int3_handler+0x39/0x100 Call Trace: <IRQ> do_int3+0xd/0xf0 int3+0x42/0x50 RIP: 0010:sched_clock+0x6/0x10 poke_int3_handler+0x39 was alternatives:958: static inline void *text_poke_addr(struct text_poke_loc *tp) { return _stext + tp->rel_addr; <------ Here is line #958 } This seems to be caused by tp (bp_patching.vec) being NULL but bp_patching.nr_entries != 0. There is a small chance for this to happen, because we have no synchronization between the zeroing of bp_patching.nr_entries and before clearing bp_patching.vec. Steve suggested we could fix this by adding sync_core(), because int3 is done with interrupts disabled, and the on_each_cpu() requires all CPUs to have had their interrupts enabled. [ mingo: Edited the comments and the changelog. ] Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Tested-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: bristot@redhat.com Fixes: c0213b0ac03c ("x86/alternative: Batch of patch operations") Link: https://lkml.kernel.org/r/157483421229.25881.15314414408559963162.stgit@devnote2 Signed-off-by: Ingo Molnar <mingo@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.