Re: [BUG REPORT] linux-next/fs-next released on 6th September fails to boot

[Christian Brauner <brauner@kernel.org>]

On Mon, Sep 09, 2024 at 01:53:24PM GMT, Chandan Babu R wrote:
> Hi,
> 
> linux-next/fs-next released on 6th September is failing to boot on a x86
> guest,
> 
> [   42.659136] Oops: general protection fault, probably for non-canonical address 0xdffffc000000000b: 0000 [#1] PREEMPT SMP KASAN NOPTI
> [   42.660501] fbcon: Taking over console
> [   42.660930] KASAN: null-ptr-deref in range [0x0000000000000058-0x000000000000005f]
> [   42.661752] CPU: 1 UID: 0 PID: 1589 Comm: dtprobed Not tainted 6.11.0-rc6+ #1
> [   42.662565] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.6.6 08/22/2023
> [   42.663472] RIP: 0010:fuse_get_req+0x36b/0x990 [fuse]
> [   42.664046] Code: 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 8c 05 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 6d 08 48 8d 7d 58 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 4d 05 00 00 f6 45 59 20 0f 85 06 03 00 00 48 83
> [   42.666945] RSP: 0018:ffffc900009a7730 EFLAGS: 00010212
> [   42.668837] RAX: dffffc0000000000 RBX: 1ffff92000134eed RCX: ffffffffc20dec9a
> [   42.670122] RDX: 000000000000000b RSI: 0000000000000008 RDI: 0000000000000058
> [   42.672154] RBP: 0000000000000000 R08: 0000000000000001 R09: ffffed1022110172
> [   42.672160] R10: ffff888110880b97 R11: ffffc900009a737a R12: 0000000000000001
> [   42.672179] R13: ffff888110880b60 R14: ffff888110880b90 R15: ffff888169973840
> [   42.672186] FS:  00007f28cd21d7c0(0000) GS:ffff8883ef280000(0000) knlGS:0000000000000000
> [   42.672191] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   42.[ CR02: ;32m00007f3237366208 CR3: 0  OK  79e001 CR4: 0000000000770ef0
> [   42.672214] PKRU: 55555554
> [   42.672218] Call Trace:
> [   42.672223]  <TASK>
> [   42.672226]  ? die_addr+0x41/0xa0
> [   42.672238]  ? exc_general_protection+0x14c/0x230
> [   42.672250]  ? asm_exc_general_protection+0x26/0x30
> [   42.672260]  ? fuse_get_req+0x77a/0x990 [fuse]
> [   42.672281]  ? fuse_get_req+0x36b/0x990 [fuse]
> [   42.672300]  ? kasan_unpoison+0x27/0x60
> [   42.672310]  ? __pfx_fuse_get_req+0x10/0x10 [fuse]
> [   42.672327]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   42.672333]  ? alloc_pages_mpol_noprof+0x195/0x440
> [   42.672340]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   42.672345]  ? kasan_unpoison+0x27/0x60
> [   42.672350]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   42.672355]  ? __kasan_slab_alloc+0x4d/0x90
> [   42.672362]  ? srso_alias_return_thunk+0x5/0xfbef5
> [   42.672367]  ? __kmalloc_cache_noprof+0x134/0x350
> [   42.672376]  fuse_simple_background+0xe7/0x180 [fuse]

I think this is basically:

fuse_simple_background()
-> !args->force
   -> fuse_get_req(NULL, fm, true);

and there you have fm->sb->s_iflags & SB_I_NOIDMAP with idmap == NULL
afaict.

That's why I'm insistent passing NULL is a problem. If I'm not mistaken
this should be fixed by Alex's patchset to not pass NULL. I'll go review
that now.