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[3.87.7.19]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8846e484ebcsm57383276d6.23.2025.11.22.03.32.48 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sat, 22 Nov 2025 03:32:50 -0800 (PST) From: Mohammad Amin Nili Message-Id: <419F2465-DA4A-41AA-B5A6-5F87E30D661C@gmail.com> Content-Type: multipart/alternative; boundary="Apple-Mail=_69BF0C82-16C0-4F57-BB12-6D3546D11E1A" X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.120.0.1.15\)) Subject: =?utf-8?Q?Re=3A_=5BHelp=5D_Microwatt_=28Zynqwatt=29_=E2=80=94_Ker?= =?utf-8?Q?nel_halts_after_Radix_MMU_init_on_booting_Linux_on_Zynq_version?= =?utf-8?Q?_of_Microwatt?= Date: Sat, 22 Nov 2025 06:32:46 -0500 In-Reply-To: Cc: linuxppc-dev@lists.ozlabs.org To: Oliver O'Halloran References: <0BCEC0A4-006A-487F-B3E8-8AA0ECB20B2D@gmail.com> X-Mailer: Apple Mail (2.3654.120.0.1.15) --Apple-Mail=_69BF0C82-16C0-4F57-BB12-6D3546D11E1A Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii Hello Oliver, > That's very odd. rcu_reclaim_tiny() is probably being folded into > rcu_process_callbacks() by the compiler and the crash occurs when > branching to the callback function from the rcu_head > = (https://elixir.bootlin.com/linux/v6.18-rc5/source/kernel/rcu/tiny.c#L95 = )= . > That said, the "callback" address it branched to (0xc00c000000000000) > is actually the base of the vmemmap (i.e. the struct page array) so I > doubt that's actually the callback address stored in the rcu_head. You > can use xmon to dump the registers and examine memory to confirm this. > It's hard to say why this is happening, but it's pretty likely to > either be the compiler optimizing away code you'd prefer to keep or a > bug in the core itself. >=20 > I'd compare the disasm of rcu_process_callbacks() with and without > your wait loop added and see how the emitted code changes. If adding > the loop changes nothing then it might be a logic bug in microwatt > itself or some other timing induced problem. I just replaced the wait-loop with the following (and it also prevents = the kernel panic): > volatile uint32_t dumb =3D 0xFEDC0000; > dumb++; - Here is the disasm of the `rcu_process_callbacks` with the injected = code: c00000000008c5e8 : c00000000008c5e8: 32 00 4c 3c addis r2,r12,50 c00000000008c5ec: 18 ca 42 38 addi r2,r2,-13800 c00000000008c5f0: a6 02 08 7c mflr r0 c00000000008c5f4: a1 c3 23 48 bl c0000000002c8994 = <_savegpr0_27> c00000000008c5f8: a1 ff 21 f8 stdu r1,-96(r1) c00000000008c5fc: fa 00 6d 88 lbz r3,250(r13) c00000000008c600: 01 00 69 60 ori r9,r3,1 c00000000008c604: fa 00 2d 99 stb r9,250(r13) c00000000008c608: 2b 01 42 3d addis r10,r2,299 c00000000008c60c: 2b 01 22 3d addis r9,r2,299 c00000000008c610: d0 3c 4a e9 ld r10,15568(r10) c00000000008c614: c8 3c 29 39 addi r9,r9,15560 c00000000008c618: 00 48 2a 7c cmpd r10,r9 c00000000008c61c: 14 00 82 40 bne c00000000008c630 = c00000000008c620: 6d d6 f8 4b bl c000000000019c8c = c00000000008c624: 00 00 00 60 nop c00000000008c628: 60 00 21 38 addi r1,r1,96 c00000000008c62c: b8 c3 23 48 b c0000000002c89e4 = <_restgpr0_27> c00000000008c630: 00 00 0a e9 ld r8,0(r10) c00000000008c634: 2b 01 e2 3c addis r7,r2,299 c00000000008c638: c8 3c e7 eb ld r31,15560(r7) c00000000008c63c: c8 3c 07 f9 std r8,15560(r7) c00000000008c640: 00 00 00 39 li r8,0 c00000000008c644: 00 00 0a f9 std r8,0(r10) c00000000008c648: 2b 01 42 3d addis r10,r2,299 c00000000008c64c: d8 3c 0a e9 ld r8,15576(r10) c00000000008c650: 2b 01 42 3d addis r10,r2,299 c00000000008c654: d0 3c 4a e9 ld r10,15568(r10) c00000000008c658: 00 50 28 7c cmpd r8,r10 c00000000008c65c: 08 00 82 40 bne c00000000008c664 = c00000000008c660: 10 00 29 f9 std r9,16(r9) c00000000008c664: 08 00 29 f9 std r9,8(r9) c00000000008c668: dc fe 80 3f lis r28,-292 <<<<=3D=3D=3D=3D=3D= =3D "THIS IS INJECTED CODE" c00000000008c66c: 21 d6 f8 4b bl c000000000019c8c = c00000000008c670: 00 00 00 60 nop c00000000008c674: 00 00 60 3b li r27,0 c00000000008c678: 00 00 3f 2c cmpdi r31,0 c00000000008c67c: ac ff 82 41 beq c00000000008c628 = c00000000008c680: 00 00 df eb ld r30,0(r31) c00000000008c684: 00 00 3e 2c cmpdi r30,0 c00000000008c688: 08 00 82 41 beq c00000000008c690 = c00000000008c68c: 2c f2 00 7c dcbtct 0,r30 c00000000008c690: 2c 00 81 93 stw r28,44(r1) c00000000008c694: 08 00 bf eb ld r29,8(r31) c00000000008c698: 00 00 3d 2c cmpdi r29,0 c00000000008c69c: 2c 00 21 81 lwz r9,44(r1) c00000000008c6a0: 01 00 29 39 addi r9,r9,1 c00000000008c6a4: 2c 00 21 91 stw r9,44(r1) c00000000008c6a8: 10 00 82 40 bne c00000000008c6b8 = c00000000008c6ac: 78 fb e3 7f mr r3,r31 c00000000008c6b0: 15 f8 03 48 bl c0000000000cbec4 = c00000000008c6b4: 00 00 00 60 nop c00000000008c6b8: 08 00 7f fb std r27,8(r31) c00000000008c6bc: 78 fb e3 7f mr r3,r31 c00000000008c6c0: a6 03 a9 7f mtctr r29 c00000000008c6c4: 78 eb ac 7f mr r12,r29 c00000000008c6c8: 18 00 41 f8 std r2,24(r1) c00000000008c6cc: 78 f3 df 7f mr r31,r30 c00000000008c6d0: 21 04 80 4e bctrl c00000000008c6d4: 18 00 41 e8 ld r2,24(r1) c00000000008c6d8: a0 ff ff 4b b c00000000008c678 = - And here is the disasm without the injected code: c00000000008c5e8 : c00000000008c5e8: 32 00 4c 3c addis r2,r12,50 c00000000008c5ec: 18 ca 42 38 addi r2,r2,-13800 c00000000008c5f0: a6 02 08 7c mflr r0 c00000000008c5f4: 95 c3 23 48 bl c0000000002c8988 = <_savegpr0_28> c00000000008c5f8: c1 ff 21 f8 stdu r1,-64(r1) c00000000008c5fc: fa 00 6d 88 lbz r3,250(r13) c00000000008c600: 01 00 69 60 ori r9,r3,1 c00000000008c604: fa 00 2d 99 stb r9,250(r13) c00000000008c608: 2b 01 42 3d addis r10,r2,299 c00000000008c60c: 2b 01 22 3d addis r9,r2,299 c00000000008c610: d0 3c 4a e9 ld r10,15568(r10) c00000000008c614: c8 3c 29 39 addi r9,r9,15560 c00000000008c618: 00 48 2a 7c cmpd r10,r9 c00000000008c61c: 14 00 82 40 bne c00000000008c630 = c00000000008c620: 6d d6 f8 4b bl c000000000019c8c = c00000000008c624: 00 00 00 60 nop c00000000008c628: 40 00 21 38 addi r1,r1,64 c00000000008c62c: ac c3 23 48 b c0000000002c89d8 = <_restgpr0_28> c00000000008c630: 00 00 0a e9 ld r8,0(r10) c00000000008c634: 2b 01 e2 3c addis r7,r2,299 c00000000008c638: c8 3c e7 eb ld r31,15560(r7) c00000000008c63c: c8 3c 07 f9 std r8,15560(r7) c00000000008c640: 00 00 00 39 li r8,0 c00000000008c644: 00 00 0a f9 std r8,0(r10) c00000000008c648: 2b 01 42 3d addis r10,r2,299 c00000000008c64c: d8 3c 0a e9 ld r8,15576(r10) c00000000008c650: 2b 01 42 3d addis r10,r2,299 c00000000008c654: d0 3c 4a e9 ld r10,15568(r10) c00000000008c658: 00 50 28 7c cmpd r8,r10 c00000000008c65c: 08 00 82 40 bne c00000000008c664 = c00000000008c660: 10 00 29 f9 std r9,16(r9) c00000000008c664: 08 00 29 f9 std r9,8(r9) c00000000008c668: 00 00 80 3b li r28,0 c00000000008c66c: 21 d6 f8 4b bl c000000000019c8c = c00000000008c670: 00 00 00 60 nop c00000000008c674: 00 00 3f 2c cmpdi r31,0 c00000000008c678: b0 ff 82 41 beq c00000000008c628 = c00000000008c67c: 00 00 df eb ld r30,0(r31) c00000000008c680: 00 00 3e 2c cmpdi r30,0 c00000000008c684: 08 00 82 41 beq c00000000008c68c = c00000000008c688: 2c f2 00 7c dcbtct 0,r30 c00000000008c68c: 08 00 bf eb ld r29,8(r31) c00000000008c690: 00 00 3d 2c cmpdi r29,0 c00000000008c694: 10 00 82 40 bne c00000000008c6a4 = c00000000008c698: 78 fb e3 7f mr r3,r31 c00000000008c69c: 19 f8 03 48 bl c0000000000cbeb4 = c00000000008c6a0: 00 00 00 60 nop c00000000008c6a4: 08 00 9f fb std r28,8(r31) c00000000008c6a8: 78 fb e3 7f mr r3,r31 c00000000008c6ac: a6 03 a9 7f mtctr r29 c00000000008c6b0: 78 eb ac 7f mr r12,r29 c00000000008c6b4: 18 00 41 f8 std r2,24(r1) c00000000008c6b8: 78 f3 df 7f mr r31,r30 c00000000008c6bc: 21 04 80 4e bctrl c00000000008c6c0: 18 00 41 e8 ld r2,24(r1) c00000000008c6c4: b0 ff ff 4b b c00000000008c674 = Sounds like some sorta compiler optimizations, right? Bests, Manili= --Apple-Mail=_69BF0C82-16C0-4F57-BB12-6D3546D11E1A Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=us-ascii Hello= Oliver,

That's very = odd. rcu_reclaim_tiny() is probably being folded into
rcu_process_callbacks() by the = compiler and the crash occurs when
branching to the callback function from the = rcu_head
(https://elixir.bootlin.com/linux/v6.18-rc5/source/kernel/rcu/ti= ny.c#L95).
That said, the "callback" = address it branched to (0xc00c000000000000)
is actually the base of the = vmemmap (i.e. the struct page array) so I
doubt that's actually the callback address stored in the = rcu_head. You
can use xmon = to dump the registers and examine memory to confirm this.
It's hard to say why this is = happening, but it's pretty likely to
either be the compiler optimizing away code you'd prefer to = keep or a
bug in the = core itself.

I'd compare = the disasm of rcu_process_callbacks() with and without
your wait loop added and see how = the emitted code changes. If adding
the loop changes nothing then it might be a logic bug in = microwatt
itself or = some other timing induced problem.

I just replaced the wait-loop with the following = (and it also prevents the
kernel panic):

>  volatile uint32_t dumb =3D = 0xFEDC0000;
> dumb++;

- Here is the disasm of the `rcu_process_callbacks` with the injected = code:

c00000000008c5e8 <rcu_process_callbacks>:
c00000000008c5e8:       32 00 4c 3c   =   addis   r2,r12,50
c00000000008c5ec: =       18 ca 42 38     addi   =  r2,r2,-13800
c00000000008c5f0:     =   a6 02 08 7c     mflr    r0
c00000000008c5f4:       a1 c3 23 48   =   bl      c0000000002c8994 = <_savegpr0_27>
c00000000008c5f8:   =     a1 ff 21 f8     stdu   =  r1,-96(r1)
c00000000008c5fc:     =   fa 00 6d 88     lbz     r3,250(r13)
c00000000008c600:       01 00 69 60   =   ori     r9,r3,1
c00000000008c604: =       fa 00 2d 99     stb     = r9,250(r13)
c00000000008c608:       = 2b 01 42 3d     addis   r10,r2,299
c00000000008c60c:       2b 01 22 3d   =   addis   r9,r2,299
c00000000008c610: =       d0 3c 4a e9     ld     =  r10,15568(r10)
c00000000008c614:   =     c8 3c 29 39     addi   =  r9,r9,15560
c00000000008c618:     =   00 48 2a 7c     cmpd    r10,r9
c00000000008c61c:       14 00 82 40   =   bne     c00000000008c630 = <rcu_process_callbacks+0x48>
c00000000008c620: =       6d d6 f8 4b     bl     =  c000000000019c8c <arch_local_irq_restore+0x8>
c00000000008c624:       00 00 00 60   =   nop
c00000000008c628:       = 60 00 21 38     addi    r1,r1,96
c00000000008c62c:       b8 c3 23 48   =   b       c0000000002c89e4 = <_restgpr0_27>
c00000000008c630:   =     00 00 0a e9     ld     =  r8,0(r10)
c00000000008c634:     =   2b 01 e2 3c     addis   r7,r2,299
c00000000008c638:       c8 3c e7 eb   =   ld      r31,15560(r7)
c00000000008c63c:       c8 3c 07 f9   =   std     r8,15560(r7)
c00000000008c640:       00 00 00 39   =   li      r8,0
c00000000008c644: =       00 00 0a f9     std     = r8,0(r10)
c00000000008c648:       2b = 01 42 3d     addis   r10,r2,299
c00000000008c64c:       d8 3c 0a e9   =   ld      r8,15576(r10)
c00000000008c650:       2b 01 42 3d   =   addis   r10,r2,299
c00000000008c654: =       d0 3c 4a e9     ld     =  r10,15568(r10)
c00000000008c658:   =     00 50 28 7c     cmpd   =  r8,r10
c00000000008c65c:       = 08 00 82 40     bne     c00000000008c664 = <rcu_process_callbacks+0x7c>
c00000000008c660: =       10 00 29 f9     std     = r9,16(r9)
c00000000008c664:       08 = 00 29 f9     std     r9,8(r9)
c00000000008c668:       dc fe 80 3f   =   lis     r28,-292 <<<<=3D=3D=3D=3D=3D=3D = "THIS IS INJECTED CODE"
c00000000008c66c:   =     21 d6 f8 4b     bl     =  c000000000019c8c <arch_local_irq_restore+0x8>
c00000000008c670:       00 00 00 60   =   nop
c00000000008c674:       = 00 00 60 3b     li      r27,0
c00000000008c678:       00 00 3f 2c   =   cmpdi   r31,0
c00000000008c67c:   =     ac ff 82 41     beq     = c00000000008c628 <rcu_process_callbacks+0x40>
c00000000008c680:       00 00 df eb   =   ld      r30,0(r31)
c00000000008c684:       00 00 3e 2c   =   cmpdi   r30,0
c00000000008c688:   =     08 00 82 41     beq     = c00000000008c690 <rcu_process_callbacks+0xa8>
c00000000008c68c:       2c f2 00 7c   =   dcbtct  0,r30
c00000000008c690:   =     2c 00 81 93     stw     = r28,44(r1)
c00000000008c694:       = 08 00 bf eb     ld      r29,8(r31)
c00000000008c698:       00 00 3d 2c   =   cmpdi   r29,0
c00000000008c69c:   =     2c 00 21 81     lwz     = r9,44(r1)
c00000000008c6a0:       01 = 00 29 39     addi    r9,r9,1
c00000000008c6a4:       2c 00 21 91   =   stw     r9,44(r1)
c00000000008c6a8: =       10 00 82 40     bne     = c00000000008c6b8 <rcu_process_callbacks+0xd0>
c00000000008c6ac:       78 fb e3 7f   =   mr      r3,r31
c00000000008c6b0:       15 f8 03 48   =   bl      c0000000000cbec4 = <kmem_dump_obj+0x8>
c00000000008c6b4:   =     00 00 00 60     nop
c00000000008c6b8:       08 00 7f fb   =   std     r27,8(r31)
c00000000008c6bc:=       78 fb e3 7f     mr     =  r3,r31
c00000000008c6c0:       = a6 03 a9 7f     mtctr   r29
c00000000008c6c4:       78 eb ac 7f   =   mr      r12,r29
c00000000008c6c8:       18 00 41 f8   =   std     r2,24(r1)
c00000000008c6cc: =       78 f3 df 7f     mr     =  r31,r30
c00000000008c6d0:     =   21 04 80 4e     bctrl
c00000000008c6d4:       18 00 41 e8   =   ld      r2,24(r1)
c00000000008c6d8:       a0 ff ff 4b   =   b       c00000000008c678 = <rcu_process_callbacks+0x90>

- And here is the disasm without the = injected code:

c00000000008c5e8 = <rcu_process_callbacks>:
c00000000008c5e8: =       32 00 4c 3c     addis   = r2,r12,50
c00000000008c5ec:       18 = ca 42 38     addi    r2,r2,-13800
c00000000008c5f0:       a6 02 08 7c   =   mflr    r0
c00000000008c5f4: =       95 c3 23 48     bl     =  c0000000002c8988 <_savegpr0_28>
c00000000008c5f8:       c1 ff 21 f8   =   stdu    r1,-64(r1)
c00000000008c5fc:=       fa 00 6d 88     lbz     = r3,250(r13)
c00000000008c600:       = 01 00 69 60     ori     r9,r3,1
c00000000008c604:       fa 00 2d 99   =   stb     r9,250(r13)
c00000000008c608:       2b 01 42 3d   =   addis   r10,r2,299
c00000000008c60c: =       2b 01 22 3d     addis   = r9,r2,299
c00000000008c610:       d0 = 3c 4a e9     ld      r10,15568(r10)
c00000000008c614:       c8 3c 29 39   =   addi    r9,r9,15560
c00000000008c618:       00 48 2a 7c   =   cmpd    r10,r9
c00000000008c61c: =       14 00 82 40     bne     = c00000000008c630 <rcu_process_callbacks+0x48>
c00000000008c620:       6d d6 f8 4b   =   bl      c000000000019c8c = <arch_local_irq_restore+0x8>
c00000000008c624: =       00 00 00 60     nop
c00000000008c628:       40 00 21 38   =   addi    r1,r1,64
c00000000008c62c: =       ac c3 23 48     b       = c0000000002c89d8 <_restgpr0_28>
c00000000008c630:       00 00 0a e9   =   ld      r8,0(r10)
c00000000008c634:       2b 01 e2 3c   =   addis   r7,r2,299
c00000000008c638: =       c8 3c e7 eb     ld     =  r31,15560(r7)
c00000000008c63c:     =   c8 3c 07 f9     std     = r8,15560(r7)
c00000000008c640:       = 00 00 00 39     li      r8,0
c00000000008c644:       00 00 0a f9   =   std     r8,0(r10)
c00000000008c648: =       2b 01 42 3d     addis   = r10,r2,299
c00000000008c64c:       = d8 3c 0a e9     ld      r8,15576(r10)
c00000000008c650:       2b 01 42 3d   =   addis   r10,r2,299
c00000000008c654: =       d0 3c 4a e9     ld     =  r10,15568(r10)
c00000000008c658:   =     00 50 28 7c     cmpd   =  r8,r10
c00000000008c65c:       = 08 00 82 40     bne     c00000000008c664 = <rcu_process_callbacks+0x7c>
c00000000008c660: =       10 00 29 f9     std     = r9,16(r9)
c00000000008c664:       08 = 00 29 f9     std     r9,8(r9)
c00000000008c668:       00 00 80 3b   =   li      r28,0
c00000000008c66c:=       21 d6 f8 4b     bl     =  c000000000019c8c <arch_local_irq_restore+0x8>
c00000000008c670:       00 00 00 60   =   nop
c00000000008c674:       = 00 00 3f 2c     cmpdi   r31,0
c00000000008c678:       b0 ff 82 41   =   beq     c00000000008c628 = <rcu_process_callbacks+0x40>
c00000000008c67c: =       00 00 df eb     ld     =  r30,0(r31)
c00000000008c680:     =   00 00 3e 2c     cmpdi   r30,0
c00000000008c684:       08 00 82 41   =   beq     c00000000008c68c = <rcu_process_callbacks+0xa4>
c00000000008c688: =       2c f2 00 7c     dcbtct =  0,r30
c00000000008c68c:       = 08 00 bf eb     ld      r29,8(r31)
c00000000008c690:       00 00 3d 2c   =   cmpdi   r29,0
c00000000008c694:   =     10 00 82 40     bne     = c00000000008c6a4 <rcu_process_callbacks+0xbc>
c00000000008c698:       78 fb e3 7f   =   mr      r3,r31
c00000000008c69c:       19 f8 03 48   =   bl      c0000000000cbeb4 = <kmem_dump_obj+0x8>
c00000000008c6a0:   =     00 00 00 60     nop
c00000000008c6a4:       08 00 9f fb   =   std     r28,8(r31)
c00000000008c6a8:=       78 fb e3 7f     mr     =  r3,r31
c00000000008c6ac:       = a6 03 a9 7f     mtctr   r29
c00000000008c6b0:       78 eb ac 7f   =   mr      r12,r29
c00000000008c6b4:       18 00 41 f8   =   std     r2,24(r1)
c00000000008c6b8: =       78 f3 df 7f     mr     =  r31,r30
c00000000008c6bc:     =   21 04 80 4e     bctrl
c00000000008c6c0:       18 00 41 e8   =   ld      r2,24(r1)
c00000000008c6c4:       b0 ff ff 4b   =   b       c00000000008c674 = <rcu_process_callbacks+0x8c>


Sounds like some sorta compiler optimizations, = right?

Bests,
Manili
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