The quilt patch titled Subject: x86/kgdb: fix hang on failed breakpoint removal has been removed from the -mm tree. Its filename was x86-kgdb-fix-hang-on-failed-breakpoint-removal.patch

This patch was dropped because an updated version will be issued

------------------------------------------------------ From: Florian Rommel mail@florommel.de Subject: x86/kgdb: fix hang on failed breakpoint removal Date: Mon, 12 Aug 2024 01:22:08 +0200

On x86, occasionally, the removal of a breakpoint (i.e., removal of the int3 instruction) fails because the text_mutex is taken by another CPU (mainly due to the static_key mechanism, I think). The function kgdb_skipexception catches exceptions from these spurious int3 instructions, bails out of KGDB, and continues execution from the previous PC address.

However, this led to an endless loop between the int3 instruction and kgdb_skipexception since the int3 instruction (being still present) triggered again. This effectively caused the system to hang.

With this patch, we try to remove the concerned spurious int3 instruction in kgdb_skipexception before continuing execution. This may take a few attempts until the concurrent holders of the text_mutex have released it, but eventually succeeds and the kernel can continue.

Link: https://lkml.kernel.org/r/20240811232208.234261-3-mail@florommel.de Signed-off-by: Florian Rommel mail@florommel.de Cc: Borislav Petkov bp@alien8.de Cc: Christophe JAILLET christophe.jaillet@wanadoo.fr Cc: Christophe Leroy christophe.leroy@csgroup.eu Cc: Daniel Thompson daniel.thompson@linaro.org Cc: Dave Hansen dave.hansen@linux.intel.com Cc: Douglas Anderson dianders@chromium.org Cc: Geert Uytterhoeven geert+renesas@glider.be Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: Jason Wessel jason.wessel@windriver.com Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Peter Zijlstra (Intel) peterz@infradead.org Cc: Randy Dunlap rdunlap@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

arch/x86/kernel/kgdb.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+)

--- a/arch/x86/kernel/kgdb.c~x86-kgdb-fix-hang-on-failed-breakpoint-removal +++ a/arch/x86/kernel/kgdb.c @@ -723,7 +723,31 @@ void kgdb_arch_exit(void) int kgdb_skipexception(int exception, struct pt_regs *regs) { if (exception == 3 && kgdb_isremovedbreak(regs->ip - 1)) { + struct kgdb_bkpt *bpt; + int i, error; + regs->ip -= 1; + + /* + * Try to remove the spurious int3 instruction. + * These int3s can result from failed breakpoint removals + * in kgdb_arch_remove_breakpoint. + */ + for (bpt = NULL, i = 0; i < KGDB_MAX_BREAKPOINTS; i++) { + if (kgdb_break[i].bpt_addr == regs->ip && + kgdb_break[i].state == BP_REMOVED && + (kgdb_break[i].type == BP_BREAKPOINT || + kgdb_break[i].type == BP_POKE_BREAKPOINT)) { + bpt = &kgdb_break[i]; + break; + } + } + if (!bpt) + return 1; + error = kgdb_arch_remove_breakpoint(bpt); + if (error) + pr_err("skipexception: breakpoint remove failed: %lx\n", + bpt->bpt_addr); return 1; } return 0; _

Patches currently in -mm which might be from mail@florommel.de are