The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.14.y git checkout FETCH_HEAD git cherry-pick -x 41a506ef71eb38d94fe133f565c87c3e06ccc072 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2023080741-polka-twice-b0df@gregkh' --subject-prefix 'PATCH 4.14.y' HEAD^.. Possible dependencies: 41a506ef71eb ("powerpc/ftrace: Create a dummy stackframe to fix stack unwind") a5f04d1f2724 ("powerpc/ftrace: Regroup PPC64 specific operations in ftrace_mprofile.S") 228216716cb5 ("powerpc/ftrace: Refactor ftrace_{regs_}caller") 9bdb2eec3dde ("powerpc/ftrace: Don't use lmw/stmw in ftrace_regs_caller()") 76b372814b08 ("powerpc/ftrace: Style cleanup in ftrace_mprofile.S") fc75f8733798 ("powerpc/ftrace: Have arch_ftrace_get_regs() return NULL unless FL_SAVE_REGS is set") 34d8dac807f0 ("powerpc/ftrace: Also save r1 in ftrace_caller()") 4ee83a2cfbc4 ("powerpc/ftrace: Remove ftrace_32.S") 41315494beed ("powerpc/ftrace: Prepare ftrace_64_mprofile.S for reuse by PPC32") 830213786c49 ("powerpc/ftrace: directly call of function graph tracer by ftrace caller") 0c81ed5ed438 ("powerpc/ftrace: Refactor ftrace_{en/dis}able_ftrace_graph_caller") 40b035efe288 ("powerpc/ftrace: Implement CONFIG_DYNAMIC_FTRACE_WITH_ARGS") c75388a8ceff ("powerpc/ftrace: Prepare PPC64's ftrace_caller() for CONFIG_DYNAMIC_FTRACE_WITH_ARGS") d95bf254be5f ("powerpc/ftrace: Prepare PPC32's ftrace_caller() for CONFIG_DYNAMIC_FTRACE_WITH_ARGS") 7bdb478c1d15 ("powerpc/ftrace: Simplify PPC32's return_to_handler()") 7875bc9b07cd ("powerpc/ftrace: Don't save again LR in ftrace_regs_caller() on PPC32") c545b9f040f3 ("powerpc/inst: Define ppc_inst_t") aebd1fb45c62 ("powerpc: flexible GPR range save/restore macros") 7dfbfb87c243 ("powerpc/ftrace: Activate HAVE_DYNAMIC_FTRACE_WITH_REGS on PPC32") c93d4f6ecf4b ("powerpc/ftrace: Add module_trampoline_target() for PPC32") thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 41a506ef71eb38d94fe133f565c87c3e06ccc072 Mon Sep 17 00:00:00 2001 From: Naveen N Rao <naveen@xxxxxxxxxx> Date: Wed, 21 Jun 2023 10:43:49 +0530 Subject: [PATCH] powerpc/ftrace: Create a dummy stackframe to fix stack unwind With ppc64 -mprofile-kernel and ppc32 -pg, profiling instructions to call into ftrace are emitted right at function entry. The instruction sequence used is minimal to reduce overhead. Crucially, a stackframe is not created for the function being traced. This breaks stack unwinding since the function being traced does not have a stackframe for itself. As such, it never shows up in the backtrace: /sys/kernel/debug/tracing # echo 1 > /proc/sys/kernel/stack_tracer_enabled /sys/kernel/debug/tracing # cat stack_trace Depth Size Location (17 entries) ----- ---- -------- 0) 4144 32 ftrace_call+0x4/0x44 1) 4112 432 get_page_from_freelist+0x26c/0x1ad0 2) 3680 496 __alloc_pages+0x290/0x1280 3) 3184 336 __folio_alloc+0x34/0x90 4) 2848 176 vma_alloc_folio+0xd8/0x540 5) 2672 272 __handle_mm_fault+0x700/0x1cc0 6) 2400 208 handle_mm_fault+0xf0/0x3f0 7) 2192 80 ___do_page_fault+0x3e4/0xbe0 8) 2112 160 do_page_fault+0x30/0xc0 9) 1952 256 data_access_common_virt+0x210/0x220 10) 1696 400 0xc00000000f16b100 11) 1296 384 load_elf_binary+0x804/0x1b80 12) 912 208 bprm_execve+0x2d8/0x7e0 13) 704 64 do_execveat_common+0x1d0/0x2f0 14) 640 160 sys_execve+0x54/0x70 15) 480 64 system_call_exception+0x138/0x350 16) 416 416 system_call_common+0x160/0x2c4 Fix this by having ftrace create a dummy stackframe for the function being traced. With this, backtraces now capture the function being traced: /sys/kernel/debug/tracing # cat stack_trace Depth Size Location (17 entries) ----- ---- -------- 0) 3888 32 _raw_spin_trylock+0x8/0x70 1) 3856 576 get_page_from_freelist+0x26c/0x1ad0 2) 3280 64 __alloc_pages+0x290/0x1280 3) 3216 336 __folio_alloc+0x34/0x90 4) 2880 176 vma_alloc_folio+0xd8/0x540 5) 2704 416 __handle_mm_fault+0x700/0x1cc0 6) 2288 96 handle_mm_fault+0xf0/0x3f0 7) 2192 48 ___do_page_fault+0x3e4/0xbe0 8) 2144 192 do_page_fault+0x30/0xc0 9) 1952 608 data_access_common_virt+0x210/0x220 10) 1344 16 0xc0000000334bbb50 11) 1328 416 load_elf_binary+0x804/0x1b80 12) 912 64 bprm_execve+0x2d8/0x7e0 13) 848 176 do_execveat_common+0x1d0/0x2f0 14) 672 192 sys_execve+0x54/0x70 15) 480 64 system_call_exception+0x138/0x350 16) 416 416 system_call_common+0x160/0x2c4 This results in two additional stores in the ftrace entry code, but produces reliable backtraces. Fixes: 153086644fd1 ("powerpc/ftrace: Add support for -mprofile-kernel ftrace ABI") Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Naveen N Rao <naveen@xxxxxxxxxx> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Link: https://msgid.link/20230621051349.759567-1-naveen@xxxxxxxxxx diff --git a/arch/powerpc/kernel/trace/ftrace_mprofile.S b/arch/powerpc/kernel/trace/ftrace_mprofile.S index ffb1db386849..1f7d86de1538 100644 --- a/arch/powerpc/kernel/trace/ftrace_mprofile.S +++ b/arch/powerpc/kernel/trace/ftrace_mprofile.S @@ -33,6 +33,9 @@ * and then arrange for the ftrace function to be called. */ .macro ftrace_regs_entry allregs + /* Create a minimal stack frame for representing B */ + PPC_STLU r1, -STACK_FRAME_MIN_SIZE(r1) + /* Create our stack frame + pt_regs */ PPC_STLU r1,-SWITCH_FRAME_SIZE(r1) @@ -42,7 +45,7 @@ #ifdef CONFIG_PPC64 /* Save the original return address in A's stack frame */ - std r0, LRSAVE+SWITCH_FRAME_SIZE(r1) + std r0, LRSAVE+SWITCH_FRAME_SIZE+STACK_FRAME_MIN_SIZE(r1) /* Ok to continue? */ lbz r3, PACA_FTRACE_ENABLED(r13) cmpdi r3, 0 @@ -77,6 +80,8 @@ mflr r7 /* Save it as pt_regs->nip */ PPC_STL r7, _NIP(r1) + /* Also save it in B's stackframe header for proper unwind */ + PPC_STL r7, LRSAVE+SWITCH_FRAME_SIZE(r1) /* Save the read LR in pt_regs->link */ PPC_STL r0, _LINK(r1) @@ -142,7 +147,7 @@ #endif /* Pop our stack frame */ - addi r1, r1, SWITCH_FRAME_SIZE + addi r1, r1, SWITCH_FRAME_SIZE+STACK_FRAME_MIN_SIZE #ifdef CONFIG_LIVEPATCH_64 /* Based on the cmpd above, if the NIP was altered handle livepatch */
