See https://github.com/containers/bootc/issues/485#issue-2262150728 The basic setup here is: - running a podman machine (Linux VM) which has a 9p mount back out to the host (user home directory) - Our bootc install process creates a loopback mount in the VM on top of a file in the host and writes a filesystem that way We're hitting this WARN_ON as of recently: https://github.com/torvalds/linux/commit/85dd2c8ff368b1446be9febde84afe1d7aec4261 ``` Apr 24 16:35:19 localhost.localdomain kernel: ------------[ cut here ]------------ Apr 24 16:35:19 localhost.localdomain kernel: WARNING: CPU: 3 PID: 2827 at fs/netfs/iterator.c:50 netfs_extract_user_iter+0x175/0x250 [netfs] Apr 24 16:35:19 localhost.localdomain kernel: Modules linked in: loop 9p netfs rfkill overlay ptp_kvm sunrpc intel_rapl_msr intel_rapl_common binfmt_misc intel_uncore_frequency_common intel_pmc_core intel_vsec pmt_telemetry pmt_class kvm_intel ppdev kvm s> Apr 24 16:35:19 localhost.localdomain kernel: CPU: 3 PID: 2827 Comm: kworker/u16:1 Not tainted 6.8.4-200.fc39.x86_64 #1 Apr 24 16:35:19 localhost.localdomain kernel: Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-1.fc39 04/01/2014 Apr 24 16:35:19 localhost.localdomain kernel: Workqueue: loop0 loop_workfn [loop] Apr 24 16:35:19 localhost.localdomain kernel: RIP: 0010:netfs_extract_user_iter+0x175/0x250 [netfs] Apr 24 16:35:19 localhost.localdomain kernel: Code: c6 29 fb 31 ff 89 5a f8 4c 39 d9 75 c3 4d 85 c9 0f 84 c2 00 00 00 45 39 f2 0f 83 b9 00 00 00 4d 89 cd 44 89 d3 e9 30 ff ff ff <0f> 0b 48 c7 c3 fb ff ff ff 48 8b 44 24 28 65 48 2b 04 25 28 00 00 Apr 24 16:35:19 localhost.localdomain kernel: RSP: 0018:ffffb49282c2bc60 EFLAGS: 00010202 Apr 24 16:35:19 localhost.localdomain kernel: RAX: 0000000000000000 RBX: ffff991ba6cf0e00 RCX: 0000000000000000 Apr 24 16:35:19 localhost.localdomain kernel: RDX: ffff991ba6cf0e78 RSI: 0000000000005000 RDI: ffffb49282c2bd18 Apr 24 16:35:19 localhost.localdomain kernel: RBP: ffff991b6f6b35b0 R08: ffffffffc0ee1a80 R09: 0000000000000000 Apr 24 16:35:19 localhost.localdomain kernel: R10: ffffb49282c2bc80 R11: 0000000000000001 R12: ffff991b526f02e8 Apr 24 16:35:19 localhost.localdomain kernel: R13: ffffffffc0f55b40 R14: ffffb49282c2bd18 R15: ffff991ba6cf0e00 Apr 24 16:35:19 localhost.localdomain kernel: FS: 0000000000000000(0000) GS:ffff991bbdcc0000(0000) knlGS:0000000000000000 Apr 24 16:35:19 localhost.localdomain kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 Apr 24 16:35:19 localhost.localdomain kernel: CR2: 00007f01d8001018 CR3: 0000000006930006 CR4: 0000000000770ef0 Apr 24 16:35:19 localhost.localdomain kernel: PKRU: 55555554 Apr 24 16:35:19 localhost.localdomain kernel: Call Trace: Apr 24 16:35:19 localhost.localdomain kernel: <TASK> Apr 24 16:35:19 localhost.localdomain kernel: ? netfs_extract_user_iter+0x175/0x250 [netfs] Apr 24 16:35:19 localhost.localdomain kernel: ? __warn+0x81/0x130 Apr 24 16:35:19 localhost.localdomain kernel: ? netfs_extract_user_iter+0x175/0x250 [netfs] Apr 24 16:35:19 localhost.localdomain kernel: ? report_bug+0x171/0x1a0 Apr 24 16:35:19 localhost.localdomain kernel: ? handle_bug+0x3c/0x80 Apr 24 16:35:19 localhost.localdomain kernel: ? exc_invalid_op+0x17/0x70 Apr 24 16:35:19 localhost.localdomain kernel: ? asm_exc_invalid_op+0x1a/0x20 Apr 24 16:35:19 localhost.localdomain kernel: ? __pfx_lo_rw_aio_complete+0x10/0x10 [loop] Apr 24 16:35:19 localhost.localdomain kernel: ? netfs_extract_user_iter+0x175/0x250 [netfs] Apr 24 16:35:19 localhost.localdomain kernel: ? _raw_spin_unlock+0xe/0x30 Apr 24 16:35:19 localhost.localdomain kernel: ? __pfx_lo_rw_aio_complete+0x10/0x10 [loop] Apr 24 16:35:19 localhost.localdomain kernel: netfs_unbuffered_write_iter+0x14a/0x3c0 [netfs] Apr 24 16:35:19 localhost.localdomain kernel: lo_rw_aio.isra.0+0x29a/0x2b0 [loop] Apr 24 16:35:19 localhost.localdomain kernel: loop_process_work+0xb4/0x950 [loop] Apr 24 16:35:19 localhost.localdomain kernel: ? finish_task_switch.isra.0+0x94/0x2f0 Apr 24 16:35:19 localhost.localdomain kernel: ? __schedule+0x3f4/0x1530 Apr 24 16:35:19 localhost.localdomain kernel: process_one_work+0x171/0x340 Apr 24 16:35:19 localhost.localdomain kernel: worker_thread+0x27b/0x3a0 Apr 24 16:35:19 localhost.localdomain kernel: ? __pfx_worker_thread+0x10/0x10 Apr 24 16:35:19 localhost.localdomain kernel: kthread+0xe5/0x120 Apr 24 16:35:19 localhost.localdomain kernel: ? __pfx_kthread+0x10/0x10 Apr 24 16:35:19 localhost.localdomain kernel: ret_from_fork+0x31/0x50 Apr 24 16:35:19 localhost.localdomain kernel: ? __pfx_kthread+0x10/0x10 Apr 24 16:35:19 localhost.localdomain kernel: ret_from_fork_asm+0x1b/0x30 Apr 24 16:35:19 localhost.localdomain kernel: </TASK> Apr 24 16:35:19 localhost.localdomain kernel: ---[ end trace 0000000000000000 ]--- ``` However, that WARN_ON is old, what is relatively more recent AFAICS (xref https://github.com/containers/bootc/issues/485#issuecomment-2076127555 ) is https://github.com/torvalds/linux/commit/153a9961b551101cd38e94e26cd92fbfd198b19b which is very much relevant to this domain (direct I/O writing to a netfs). I haven't yet been able to reproduce this locally; working on it. And I'm going to try shipping a workaround (https://github.com/containers/podman-bootc/issues/15) but filing this as it would certainly be nice if we had a kernel side fix too. (That said, we also know we need to wean podman-machine off of 9p on linux and onto virtiofs which would hopefully be better here) Reproducible: Always
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