Issue with JFFS2 and a_ops->dirty_folio

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Hi everyone !

I am currently working on a Coldfire (MPC54418) and quite everything goes well, except that I can only execute one command from user space before getting a segmentation fault on the do_exit() syscall.

I tried to debug it and it appears to be failing in folio_mark_dirty() on the 'return mapping->a_ops->dirty_folio(mapping, folio);' call.

I added a VM_BUG_ON_FOLIO():
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index c2a48592c258..122ca2253263 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2857,9 +2857,9 @@ bool folio_mark_dirty(struct folio *folio)
                 */
                if (folio_test_reclaim(folio))
                        folio_clear_reclaim(folio);
-               if (mapping->a_ops->dirty_folio)
-                       return mapping->a_ops->dirty_folio(mapping, folio);
-               return noop_dirty_folio(mapping, folio);
+
+               VM_BUG_ON_FOLIO(!mapping->a_ops->dirty_folio, folio);
+               return mapping->a_ops->dirty_folio(mapping, folio);
        }

        return noop_dirty_folio(mapping, folio);

And it appears that this is because if tries unconditionally to call the a_ops->dirty_folio() function in JFFS2. The bug report is at the bottom of this mail. We see: aops:0x41340ae0

Which, in my build, leads to jffs2_file_address_operations.
And indeed, there is no .dirty_folio nor anything relating to folios in there.

I don't really know how to solve this though, as I am no expert in this specific part at all !

Thanks for your answers,
BR
JM

---

bash-5.2# ls
bin       etc       lib32     mnt       root      sys       usr
data home [ 9.730000] page: refcount:2 mapcount:1 mapping:42097964 index:0x97 pfn:0x27f01
     [    9.740000] aops:0x41340ae0 ino:b6 dentry name:"libc.so.6"
    9.740000] flags: 0x28(uptodate|lru|zone=0)
;36ml[ 9.750000] raw: 00000028 4fed39bc 4ffd9d24 42097964 00000097 00000000 00000000 00000002
inux[    9.760000] raw: 4fe02000
rc 9.760000] page dumped because: VM_BUG_ON_FOLIO(!mapping->a_ops->dirty_folio)
[m  [    9.770000] kernel BUG at mm/page-writeback.c:2861!
 [    9.770000] *** TRAP #7 ***   FORMAT=4
[    9.770000] Current process id is 24
[    9.770000] BAD KERNEL TRAP: 00000000
[    9.770000] PC: [<41058ff2>] folio_mark_dirty+0x68/0x82
[    9.770000] SR: 2010  SP: 41dcddb4  a2: 418fb710
[    9.770000] d0: 00000027    d1: 0000009e    d2: 4ffd9c24    d3: 60160000
[    9.770000] d4: 4fe03419    d5: 4ffd9c24    a0: 41dcdd00    a1: 414491f0
[    9.770000] Process ls (pid: 24, task=418fb710)
[    9.770000] Frame format=4 eff addr=413d4c3c pc=413dbd16
[    9.770000] Stack from 41dcddf0:
[ 9.770000] 00000b2d 413dea77 413dbce8 4fe03419 41dcdf1a 410750ee 4ffd9c24 00000000 [ 9.770000] ffffffff fffffffe 41dcde9e 60164000 00000001 41317ea4 41074d0c 41078bb0 [ 9.770000] 00000001 41d67034 ffffffff 41dd6600 60164000 41dd6600 41d6e3d0 41dcc000 [ 9.770000] 41d6e3fc 00000000 00000000 00000000 00000000 41dcdf5c 410753f2 41dcdf1a [ 9.770000] 41d67034 60160000 60164000 41dcde9e 41d6e3fc 41dcdef6 41dcdf1a 4102a940 [ 9.770000] 41d6e3d4 41d67344 41d6e3d0 41dc0000 00000100 00000003 4107ad24 41dcdf1a
[    9.770000] Call Trace: [<410750ee>] unmap_page_range+0x3e2/0x672
[    9.770000]  [<41317ea4>] mas_find+0x0/0xfa
[    9.770000]  [<41074d0c>] unmap_page_range+0x0/0x672
[    9.770000]  [<41078bb0>] vma_next+0x0/0x14
[    9.770000]  [<410753f2>] unmap_vmas+0x74/0x98
[    9.770000]  [<4102a940>] up_read+0x0/0x34
[    9.770000]  [<4107ad24>] exit_mmap+0xd4/0x1c0
[    9.770000]  [<410093f8>] arch_local_irq_enable+0x0/0xc
[    9.770000]  [<410093ec>] arch_local_irq_disable+0x0/0xc
[    9.770000]  [<41006bfa>] __mmput+0x2e/0x86
[    9.770000]  [<4100a168>] do_exit+0x21e/0x6f2
[    9.770000]  [<4100a7ba>] sys_exit_group+0x0/0x14
[    9.770000]  [<4100a778>] do_group_exit+0x22/0x64
[    9.770000]  [<4100a7ce>] pid_child_should_wake+0x0/0x56
[    9.770000]  [<410058c8>] system_call+0x54/0xa8
[    9.770000]
[ 9.770000] Code: bd16 4879 413d 4c3c 4eb9 4132 b30a 4e47 <2f02> 2f0b 4e90 508f 241f 265f 4e75 2f02 42a7 4eb9 4105 8f56 60ec 2f0b 266f 0008
[    9.770000] Disabling lock debugging due to kernel taint
[    9.770000] note: ls[24] exited with irqs disabled
    9.780000] Fixing recursive fault but reboot is needed!





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