autofs4 past 2.6.37: how to make it work?

[Michael Tokarev <mjt@tls.msk.ru>]

Hello.

I found out that since 2.6.37 kernel, my automount (neither
debian version 5.0.4-3.2 nor the latest 5.0.6) does not work
anymore.

Automounter starts correctly, mounts - say - /misc, and stays
there listening for events.

But the problem is that no events gets delivered to it no
matter how I try.  Accesses to /misc/foo always returns
immediately with ENOENT error, and automount (all threads
of it) is sleeping without any activity whatsoever.

I tried to bisect this issue, but faced some problems --
most kernels around the bad commit OOPSes while accessing
/misc/foo.  Here's the bisect log:

# good: [22763c5cf3690a681551162c15d34d935308c8d7] Linux 2.6.32
git bisect good 22763c5cf3690a681551162c15d34d935308c8d7
# bad: [521cb40b0c44418a4fd36dc633f575813d59a43d] Linux 2.6.38
git bisect bad 521cb40b0c44418a4fd36dc633f575813d59a43d
# skip: [b7ab39f631f505edc2bbdb86620d5493f995c9da] fs: dcache scale dentry refcount
git bisect skip b7ab39f631f505edc2bbdb86620d5493f995c9da
# good: [cb4b492ac7595aad10756fe0b04691f0965e0cfc] autofs4: rename dentry to expiring in autofs4_lookup_expiring()
git bisect good cb4b492ac7595aad10756fe0b04691f0965e0cfc
# good: [5f57cbcc02cf18f6b22ef4066bb10afeb8f930ff] fs: dcache remove d_mounted
git bisect good 5f57cbcc02cf18f6b22ef4066bb10afeb8f930ff
# skip: [ab90911ff90cdab59b31c045c3f0ae480d14f29d] Allow d_manage() to be used in RCU-walk mode
git bisect skip ab90911ff90cdab59b31c045c3f0ae480d14f29d
# skip: [cc53ce53c86924bfe98a12ea20b7465038a08792] Add a dentry op to allow processes to be held during pathwalk transit
git bisect skip cc53ce53c86924bfe98a12ea20b7465038a08792
# skip: [6651149371b842715906311b4631b8489cebf7e8] autofs4: Clean up autofs4_free_ino()
git bisect skip 6651149371b842715906311b4631b8489cebf7e8
# bad: [726a5e0688fd344110d8f2979d87f243a4ba1a48] autofs4: autofs4_get_inode() doesn't need autofs_info * argument anymore
git bisect bad 726a5e0688fd344110d8f2979d87f243a4ba1a48
# skip: [9e3fea16ba386fa549a0b2de8a203e5d412997a0] autofs4: Fix wait validation
git bisect skip 9e3fea16ba386fa549a0b2de8a203e5d412997a0
# bad: [14a2f00bde7668fe18d1c8355d26c7c96961e1f7] autofs4: autofs4_mkroot() is not different from autofs4_init_ino()
git bisect bad 14a2f00bde7668fe18d1c8355d26c7c96961e1f7
# skip: [71e469db242c2eeb00faf9caf7d9e00150c00a6e] autofs4: Clean up dentry operations
git bisect skip 71e469db242c2eeb00faf9caf7d9e00150c00a6e
# bad: [c14cc63a63e94d490ac6517a555113c30d420db4] autofs4 - fix get_next_positive_dentry()
git bisect bad c14cc63a63e94d490ac6517a555113c30d420db4
# skip: [e61da20a50d21725ff27571a6dff9468e4fb7146] autofs4: Clean up inode operations
git bisect skip e61da20a50d21725ff27571a6dff9468e4fb7146
# skip: [dd89f90d2deb9aa5bc8e1b15d726ff5c0bb2b623] autofs4: Add v4 pseudo direct mount support
git bisect skip dd89f90d2deb9aa5bc8e1b15d726ff5c0bb2b623
# skip: [8c13a676d5a56495c350f3141824a5ef6c6b4606] autofs4: Remove unused code
git bisect skip 8c13a676d5a56495c350f3141824a5ef6c6b4606
# bad: [b650c858c26bd9ba29ebc82d30f09355845a294a] autofs4: Merge the remaining dentry ops tables
git bisect bad b650c858c26bd9ba29ebc82d30f09355845a294a
# skip: [b5b801779d59165c4ecf1009009109545bd1f642] autofs4: Add d_manage() dentry operation
git bisect skip b5b801779d59165c4ecf1009009109545bd1f642
# skip: [b5b801779d59165c4ecf1009009109545bd1f642] autofs4: Add d_manage() dentry operation
git bisect skip b5b801779d59165c4ecf1009009109545bd1f642
# skip: [b5b801779d59165c4ecf1009009109545bd1f642] autofs4: Add d_manage() dentry operation
git bisect skip b5b801779d59165c4ecf1009009109545bd1f642

Kernel b5b801779d59165c4ecf1009009109545bd1f642 shows this OOPS:

[   11.700752] ------------[ cut here ]------------
[   11.703371] kernel BUG at fs/dcache.c:1304!
[   11.703371] invalid opcode: 0000 [#1] SMP
[   11.703371] last sysfs file: /sys/devices/virtual/vc/vcsa6/dev
[   11.703371] CPU 0
[   11.703371] Modules linked in: ext4 mbcache jbd2 crc16 virtio_net virtio_pci virtio_blk virtio virtio_ring nfs lockd nfs_acl auth_rpcgss sunrpc autofs4
[   11.703371]
[   11.703371] Pid: 599, comm: automount Not tainted 2.6.37+ #36 /Bochs
[   11.703371] RIP: 0010:[<ffffffff810c290c>]  [<ffffffff810c290c>] d_set_d_op+0x4c/0x60
[   11.703371] RSP: 0018:ffff88000794be70  EFLAGS: 00010286
[   11.703371] RAX: ffff8800070d7380 RBX: ffff88000794fe00 RCX: 000000000000000e
[   11.703371] RDX: 0000000000000000 RSI: ffffffffa0004500 RDI: ffff8800070ea080
[   11.703371] RBP: ffff8800070ea080 R08: 0000000000000002 R09: 0000000000000000
[   11.703371] R10: ffff88000794bdc8 R11: 0000000000000001 R12: ffff8800070056f0
[   11.703371] R13: ffff88000719b090 R14: ffff880006d8b840 R15: 0000000000000000
[   11.703371] FS:  0000000000000000(0000) GS:ffff880007c00000(0063) knlGS:00000000f6d00b70
[   11.703371] CS:  0010 DS: 002b ES: 002b CR0: 000000008005003b
[   11.703371] CR2: 00000000f6bff000 CR3: 0000000007be1000 CR4: 00000000000006b0
[   11.703371] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   11.703371] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[   11.703371] Process automount (pid: 599, threadinfo ffff88000794a000, task ffff880006860290)
[   11.703371] Stack:
[   11.703371]  ffffffffa000124a 00000000f6cfa8ac 000000000000016d ffff8800070ea080
[   11.703371]  0000000000000000 0000000000000000 ffffffff810bdcf3 ffff880006e986c0
[   11.703371]  ffff8800070d7380 000000051192d652 ffff880007901006 0000000000000000
[   11.703371] Call Trace:
[   11.703371]  [<ffffffffa000124a>] ? autofs4_dir_mkdir+0x1ba/0x1e0 [autofs4]
[   11.703371]  [<ffffffff810bdcf3>] ? sys_mkdirat+0x113/0x130
[   11.703371]  [<ffffffff8102787c>] ? cstar_dispatch+0x7/0x32
[   11.703371] Code: 10 00 00 48 83 7e 10 00 74 06 81 0f 00 20 00 00 48 83 3e 00 74 06 81 0f 00 40 00 00 48 83 7e 18 00 74 06 81 0f 00 80 00 00 f3 c3 <0f> 0b eb fe 0f 0b eb fe 66 66 66 2e 0f 1f 84 00 00 00 00 00 48
[   11.703371] RIP  [<ffffffff810c290c>] d_set_d_op+0x4c/0x60
[   11.703371]  RSP <ffff88000794be70>
[   11.754054] ---[ end trace 1c0705f21da3ac3a ]---

As far as I can see, there are users who successfully used autofs
with kernels >= 2.6.37, so I'm really curious how they did that.
No kernel since 2.6.37 and up to current 3.0 works for me.

Any hints?

Thank you!

/mjt