Re: [Xen-devel] gntdev/gntalloc and fork? - crash in gntdev

[Marek Marczykowski-GÃrecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Thu, Apr 30, 2015 at 04:47:44PM +0200, Marek Marczykowski-GÃrecki wrote:
> Hi,
> 
> What is the proper way to handle shared pages (either side - using
> gntdev or gntalloc) regarding fork and possible exec later? The child
> process do not need to access those pages in any way, but will map
> different one(s), using newly opened FD to the gntdev/gntalloc device.
> Should it unmap them and close FD to the device manually just after the
> fork? Or the process using gntdev or gntalloc should prevent using fork
> at all?
> 
> I'm asking because I get kernel oops[1] in context of such process. This
> process uses both gntdev and gntalloc. The PID reported there is a
> child, which maps additional pages (using newly opened FD to
> /dev/xen/gnt*), but I'm not sure if the crash happens before, after or
> at this second mapping (actually vchan connection), or maybe even at
> cleanup of this second mapping. The parent process keeps its mappings
> for the whole lifetime of its child. I don't have a 100% reliable way
> to reproduce this problem, but it happens quite often when I run such
> operations in a loop.

Any ideas? 

> The kernel is vanilla 3.19.3, running on Xen 4.4.2.
> 
> The kernel message:
> [74376.073464] general protection fault: 0000 [#1] SMP 
> [74376.073475] Modules linked in: fuse xt_conntrack ipt_MASQUERADE 
> nf_nat_masquerade_ipv4 iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 
> nf_nat_ipv4 nf_nat nf_conntrack ip6table_filter ip6_tables intel_rapl 
> iosf_mbi x86_pkg_temp_thermal coretemp crct10dif_pclmul crc32_pclmul 
> crc32c_intel pcspkr xen_netfront ghash_clmulni_intel nfsd auth_rpcgss nfs_acl 
> lockd grace xenfs xen_privcmd dummy_hcd udc_core xen_gntdev xen_gntalloc 
> xen_blkback sunrpc u2mfn(O) xen_evtchn xen_blkfront
> [74376.073522] CPU: 1 PID: 9377 Comm: qrexec-agent Tainted: G           O   
> 3.19.3-4.pvops.qubes.x86_64 #1
> [74376.073528] task: ffff880002442e40 ti: ffff88000032c000 task.ti: 
> ffff88000032c000
> [74376.073532] RIP: e030:[<ffffffffa00952c5>]  [<ffffffffa00952c5>] 
> unmap_if_in_range+0x15/0xd0 [xen_gntdev]
> [74376.073543] RSP: e02b:ffff88000032fc08  EFLAGS: 00010292
> [74376.073546] RAX: 0000000000000000 RBX: dead000000100100 RCX: 
> 00007fd8616ea000
> [74376.073550] RDX: 00007fd8616ea000 RSI: 00007fd8616e9000 RDI: 
> dead000000100100
> [74376.073554] RBP: ffff88000032fc48 R08: 0000000000000000 R09: 
> 0000000000000000
> [74376.073557] R10: ffffea000021bb00 R11: 0000000000000000 R12: 
> 00007fd8616e9000
> [74376.073561] R13: 00007fd8616ea000 R14: ffff880012702e40 R15: 
> ffff880012702e70
> [74376.073569] FS:  00007fd8616ca700(0000) GS:ffff880013c80000(0000) 
> knlGS:0000000000000000
> [74376.073574] CS:  e033 DS: 0000 ES: 0000 CR0: 0000000080050033
> [74376.073577] CR2: 00007fd8616e9458 CR3: 00000000e7af5000 CR4: 
> 0000000000042660
> [74376.073582] Stack:
> [74376.073584]  ffff8800188356c0 00000000000000d0 ffff88000032fc68 
> 00000000c64ef797
> [74376.073590]  0000000000000220 dead000000100100 00007fd8616e9000 
> 00007fd8616ea000
> [74376.073596]  ffff88000032fc88 ffffffffa00953c6 ffff88000032fcc8 
> ffff880012702e70
> [74376.073603] Call Trace:
> [74376.073610]  [<ffffffffa00953c6>] mn_invl_range_start+0x46/0x90 
> [xen_gntdev]
> [74376.073620]  [<ffffffff811e88fb>] 
> __mmu_notifier_invalidate_range_start+0x5b/0x90
> [74376.073627]  [<ffffffff811c2a59>] do_wp_page+0x769/0x820
> [74376.074031]  [<ffffffff811c4f5c>] handle_mm_fault+0x7fc/0x10c0
> [74376.074031]  [<ffffffff813864cd>] ? radix_tree_lookup+0xd/0x10
> [74376.074031]  [<ffffffff81061e1c>] __do_page_fault+0x1dc/0x5a0
> [74376.074031]  [<ffffffff817560a6>] ? mutex_lock+0x16/0x37
> [74376.074031]  [<ffffffffa0008928>] ? evtchn_ioctl+0x118/0x3c0 [xen_evtchn]
> [74376.074031]  [<ffffffff812209d8>] ? do_vfs_ioctl+0x2f8/0x4f0
> [74376.074031]  [<ffffffff811cafdf>] ? do_munmap+0x29f/0x3b0
> [74376.074031]  [<ffffffff81062211>] do_page_fault+0x31/0x70
> [74376.074031]  [<ffffffff81759e28>] page_fault+0x28/0x30
> [74376.074031] Code: e9 dd fd ff ff 31 c9 31 db e9 20 fe ff ff 0f 1f 84 00 00 
> 00 00 00 66 66 66 66 90 55 48 89 e5 41 55 41 54 53 48 89 fb 48 83 ec 28 <48> 
> 8b 47 10 48 85 c0 74 4e 4c 8b 00 49 39 d0 73 46 4c 8b 48 08
> [74376.074031] RIP  [<ffffffffa00952c5>] unmap_if_in_range+0x15/0xd0 
> [xen_gntdev]
> [74376.074031]  RSP <ffff88000032fc08>
> [74376.091682] ---[ end trace 2b21c5b714eb1071 ]---
> [74404.069009] NMI watchdog: BUG: soft lockup - CPU#2 stuck for 23s! 
> [qrexec-agent:9379]
> [74404.069009] Modules linked in: fuse xt_conntrack ipt_MASQUERADE 
> nf_nat_masquerade_ipv4 iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 
> nf_nat_ipv4 nf_nat nf_conntrack ip6table_filter ip6_tables intel_rapl 
> iosf_mbi x86_pkg_temp_thermal coretemp crct10dif_pclmul crc32_pclmul 
> crc32c_intel pcspkr xen_netfront ghash_clmulni_intel nfsd auth_rpcgss nfs_acl 
> lockd grace xenfs xen_privcmd dummy_hcd udc_core xen_gntdev xen_gntalloc 
> xen_blkback sunrpc u2mfn(O) xen_evtchn xen_blkfront
> [74404.069009] CPU: 2 PID: 9379 Comm: qrexec-agent Tainted: G      D    O   
> 3.19.3-4.pvops.qubes.x86_64 #1
> [74404.069009] task: ffff880010e24a00 ti: ffff880002470000 task.ti: 
> ffff880002470000
> [74404.069009] RIP: e030:[<ffffffff81757b11>]  [<ffffffff81757b11>] 
> _raw_spin_lock+0x21/0x30
> [74404.069009] RSP: e02b:ffff880002473e18  EFLAGS: 00000297
> [74404.069009] RAX: 0000000000000040 RBX: ffff880002345c00 RCX: 
> 0000000000018cf8
> [74404.069009] RDX: 0000000000000041 RSI: ffff880002345c00 RDI: 
> ffff880012702e60
> [74404.069009] RBP: ffff880002473e18 R08: ffff880012702240 R09: 
> 00000001802a0019
> [74404.069009] R10: ffffea000049c080 R11: ffffffffa00955bf R12: 
> ffff880012702e70
> [74404.069009] R13: ffff880012702e40 R14: ffff8800132c6f20 R15: 
> ffff880012b163c0
> [74404.069009] FS:  00007fd8616ca700(0000) GS:ffff880013d00000(0000) 
> knlGS:0000000000000000
> [74404.069009] CS:  e033 DS: 0000 ES: 0000 CR0: 0000000080050033
> [74404.069009] CR2: 00007fd8610be098 CR3: 000000000b971000 CR4: 
> 0000000000042660
> [74404.069009] Stack:
> [74404.069009]  ffff880002473e48 ffffffffa0095452 ffff880002473e48 
> ffff880002345c00
> [74404.069009]  ffff880012702e70 0000000000000000 ffff880002473e78 
> ffffffff811e8c2e
> [74404.069009]  ffff880002473e78 ffff880012702e40 ffff880012702e40 
> ffff880012d123c8
> [74404.069009] Call Trace:
> [74404.069009]  [<ffffffffa0095452>] mn_release+0x22/0x130 [xen_gntdev]
> [74404.069009]  [<ffffffff811e8c2e>] mmu_notifier_unregister+0x4e/0xe0
> [74404.069009]  [<ffffffffa00957c0>] gntdev_release+0x60/0xa0 [xen_gntdev]
> [74404.069009]  [<ffffffff8120ec0f>] __fput+0xdf/0x1e0
> [74404.069009]  [<ffffffff8120ed5e>] ____fput+0xe/0x10
> [74404.069009]  [<ffffffff810b56df>] task_work_run+0xbf/0x100
> [74404.069009]  [<ffffffff81014c47>] do_notify_resume+0x97/0xb0
> [74404.069009]  [<ffffffff81758127>] int_signal+0x12/0x17
> [74404.069009] Code: 66 2e 0f 1f 84 00 00 00 00 00 66 66 66 66 90 55 48 89 e5 
> b8 00 01 00 00 f0 66 0f c1 07 0f b6 d4 38 c2 75 04 5d c3 f3 90 0f b6 07 <38> 
> d0 75 f7 5d c3 66 0f 1f 84 00 00 00 00 00 66 66 66 66 90 55
> 
> 

-- 
Best Regards,
Marek Marczykowski-GÃrecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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