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SubjectRe: [PATCH] RCU: don't turn off lockdep when find suspicious rcu_dereference_check() usage
On Tue, Apr 20, 2010 at 11:38:28AM -0400, Miles Lane wrote:
> Excellent. Here are the results on my machine. .config appended.

First, thank you very much for testing this, Miles!

> [ 0.177300] [ INFO: suspicious rcu_dereference_check() usage. ]
> [ 0.177428] ---------------------------------------------------
> [ 0.177557] include/linux/cgroup.h:533 invoked
> rcu_dereference_check() without protection!
> [ 0.177760]
> [ 0.177761] other info that might help us debug this:
> [ 0.177762]
> [ 0.178123]
> [ 0.178124] rcu_scheduler_active = 1, debug_locks = 1
> [ 0.178369] no locks held by watchdog/0/5.
> [ 0.178493]
> [ 0.178494] stack backtrace:
> [ 0.178735] Pid: 5, comm: watchdog/0 Not tainted 2.6.34-rc5 #18
> [ 0.178863] Call Trace:
> [ 0.178994] [<ffffffff81067fc2>] lockdep_rcu_dereference+0x9d/0xa5
> [ 0.179127] [<ffffffff8102d667>] task_subsys_state+0x48/0x60
> [ 0.179259] [<ffffffff810328e5>] __sched_setscheduler+0x19d/0x300
> [ 0.179392] [<ffffffff8102b477>] ? need_resched+0x1e/0x28
> [ 0.179523] [<ffffffff813cd501>] ? schedule+0x643/0x66e
> [ 0.179653] [<ffffffff81091903>] ? watchdog+0x0/0x8c
> [ 0.179783] [<ffffffff81032a63>] sched_setscheduler+0xe/0x10
> [ 0.179913] [<ffffffff8109192d>] watchdog+0x2a/0x8c
> [ 0.180010] [<ffffffff81091903>] ? watchdog+0x0/0x8c
> [ 0.180142] [<ffffffff8105713e>] kthread+0x89/0x91
> [ 0.180272] [<ffffffff81068922>] ? trace_hardirqs_on_caller+0x114/0x13f
> [ 0.180405] [<ffffffff81003994>] kernel_thread_helper+0x4/0x10
> [ 0.180537] [<ffffffff813cfcc0>] ? restore_args+0x0/0x30
> [ 0.180667] [<ffffffff810570b5>] ? kthread+0x0/0x91
> [ 0.180796] [<ffffffff81003990>] ? kernel_thread_helper+0x0/0x10

I have a prototype patch for this way down below, but someone who knows
more about CONFIG_RT_GROUP_SCHED than I do should look it over. In the
meantime, could you please see if it helps?

> [ 3.116754] [ INFO: suspicious rcu_dereference_check() usage. ]
> [ 3.116754] ---------------------------------------------------
> [ 3.116754] kernel/cgroup.c:4432 invoked rcu_dereference_check()
> without protection!
> [ 3.116754]
> [ 3.116754] other info that might help us debug this:
> [ 3.116754]
> [ 3.116754]
> [ 3.116754] rcu_scheduler_active = 1, debug_locks = 1
> [ 3.116754] 2 locks held by async/1/666:
> [ 3.116754] #0: (&shost->scan_mutex){+.+.+.}, at:
> [<ffffffff812df0a0>] __scsi_add_device+0x83/0xe4
> [ 3.116754] #1: (&(&blkcg->lock)->rlock){......}, at:
> [<ffffffff811f2e8d>] blkiocg_add_blkio_group+0x29/0x7f
> [ 3.116754]
> [ 3.116754] stack backtrace:
> [ 3.116754] Pid: 666, comm: async/1 Not tainted 2.6.34-rc5 #18
> [ 3.116754] Call Trace:
> [ 3.116754] [<ffffffff81067fc2>] lockdep_rcu_dereference+0x9d/0xa5
> [ 3.116754] [<ffffffff8107f9b1>] css_id+0x3f/0x51
> [ 3.116754] [<ffffffff811f2e9c>] blkiocg_add_blkio_group+0x38/0x7f
> [ 3.116754] [<ffffffff811f4e64>] cfq_init_queue+0xdf/0x2dc
> [ 3.116754] [<ffffffff811e3445>] elevator_init+0xba/0xf5
> [ 3.116754] [<ffffffff812dc02a>] ? scsi_request_fn+0x0/0x451
> [ 3.116754] [<ffffffff811e696b>] blk_init_queue_node+0x12f/0x135
> [ 3.116754] [<ffffffff811e697d>] blk_init_queue+0xc/0xe
> [ 3.116754] [<ffffffff812dc49c>] __scsi_alloc_queue+0x21/0x111
> [ 3.116754] [<ffffffff812dc5a4>] scsi_alloc_queue+0x18/0x64
> [ 3.116754] [<ffffffff812de5a0>] scsi_alloc_sdev+0x19e/0x256
> [ 3.116754] [<ffffffff812de73e>] scsi_probe_and_add_lun+0xe6/0x9c5
> [ 3.116754] [<ffffffff81068922>] ? trace_hardirqs_on_caller+0x114/0x13f
> [ 3.116754] [<ffffffff813ce0d6>] ? __mutex_lock_common+0x3e4/0x43a
> [ 3.116754] [<ffffffff812df0a0>] ? __scsi_add_device+0x83/0xe4
> [ 3.116754] [<ffffffff812d0a5c>] ? transport_setup_classdev+0x0/0x17
> [ 3.116754] [<ffffffff812df0a0>] ? __scsi_add_device+0x83/0xe4
> [ 3.116754] [<ffffffff812df0d5>] __scsi_add_device+0xb8/0xe4
> [ 3.116754] [<ffffffff812ea9c5>] ata_scsi_scan_host+0x74/0x16e
> [ 3.116754] [<ffffffff81057685>] ? autoremove_wake_function+0x0/0x34
> [ 3.116754] [<ffffffff812e8e64>] async_port_probe+0xab/0xb7
> [ 3.116754] [<ffffffff8105e1b5>] ? async_thread+0x0/0x1f4
> [ 3.116754] [<ffffffff8105e2ba>] async_thread+0x105/0x1f4
> [ 3.116754] [<ffffffff81033d79>] ? default_wake_function+0x0/0xf
> [ 3.116754] [<ffffffff8105e1b5>] ? async_thread+0x0/0x1f4
> [ 3.116754] [<ffffffff8105713e>] kthread+0x89/0x91
> [ 3.116754] [<ffffffff81068922>] ? trace_hardirqs_on_caller+0x114/0x13f
> [ 3.116754] [<ffffffff81003994>] kernel_thread_helper+0x4/0x10
> [ 3.116754] [<ffffffff813cfcc0>] ? restore_args+0x0/0x30
> [ 3.116754] [<ffffffff810570b5>] ? kthread+0x0/0x91
> [ 3.116754] [<ffffffff81003990>] ? kernel_thread_helper+0x0/0x10

I cannot convince myself that the above access is safe. Vivek, Nauman,
thoughts?

> [ 33.425087] [ INFO: suspicious rcu_dereference_check() usage. ]
> [ 33.425090] ---------------------------------------------------
> [ 33.425094] net/core/dev.c:1993 invoked rcu_dereference_check()
> without protection!
> [ 33.425098]
> [ 33.425098] other info that might help us debug this:
> [ 33.425100]
> [ 33.425103]
> [ 33.425104] rcu_scheduler_active = 1, debug_locks = 1
> [ 33.425108] 2 locks held by canberra-gtk-pl/4208:
> [ 33.425111] #0: (sk_lock-AF_INET){+.+.+.}, at:
> [<ffffffff81394ffd>] inet_stream_connect+0x3a/0x24d
> [ 33.425125] #1: (rcu_read_lock_bh){.+....}, at:
> [<ffffffff8134a809>] dev_queue_xmit+0x14e/0x4b8
> [ 33.425137]
> [ 33.425138] stack backtrace:
> [ 33.425142] Pid: 4208, comm: canberra-gtk-pl Not tainted 2.6.34-rc5 #18
> [ 33.425146] Call Trace:
> [ 33.425154] [<ffffffff81067fc2>] lockdep_rcu_dereference+0x9d/0xa5
> [ 33.425161] [<ffffffff8134a914>] dev_queue_xmit+0x259/0x4b8
> [ 33.425167] [<ffffffff8134a809>] ? dev_queue_xmit+0x14e/0x4b8
> [ 33.425173] [<ffffffff81041c52>] ? _local_bh_enable_ip+0xcd/0xda
> [ 33.425180] [<ffffffff8135375a>] neigh_resolve_output+0x234/0x285
> [ 33.425188] [<ffffffff8136f71f>] ip_finish_output2+0x257/0x28c
> [ 33.425193] [<ffffffff8136f7bc>] ip_finish_output+0x68/0x6a
> [ 33.425198] [<ffffffff813704b3>] T.866+0x52/0x59
> [ 33.425203] [<ffffffff813706fe>] ip_output+0xaa/0xb4
> [ 33.425209] [<ffffffff8136ebb8>] ip_local_out+0x20/0x24
> [ 33.425215] [<ffffffff8136f204>] ip_queue_xmit+0x309/0x368
> [ 33.425223] [<ffffffff810e41e6>] ? __kmalloc_track_caller+0x111/0x155
> [ 33.425230] [<ffffffff813831ef>] ? tcp_connect+0x223/0x3d3
> [ 33.425236] [<ffffffff81381971>] tcp_transmit_skb+0x707/0x745
> [ 33.425243] [<ffffffff81383342>] tcp_connect+0x376/0x3d3
> [ 33.425250] [<ffffffff81268ac3>] ? secure_tcp_sequence_number+0x55/0x6f
> [ 33.425256] [<ffffffff813872f0>] tcp_v4_connect+0x3df/0x455
> [ 33.425263] [<ffffffff8133cbd9>] ? lock_sock_nested+0xf3/0x102
> [ 33.425269] [<ffffffff81395067>] inet_stream_connect+0xa4/0x24d
> [ 33.425276] [<ffffffff8133b418>] sys_connect+0x90/0xd0
> [ 33.425283] [<ffffffff81002b9c>] ? sysret_check+0x27/0x62
> [ 33.425289] [<ffffffff81068922>] ? trace_hardirqs_on_caller+0x114/0x13f
> [ 33.425296] [<ffffffff813ced00>] ? trace_hardirqs_on_thunk+0x3a/0x3f
> [ 33.425303] [<ffffffff81002b6b>] system_call_fastpath+0x16/0x1b

This looks like an rcu_dereference() needs to instead be
rcu_dereference_bh(), but the line numbering in my version of
net/core/dev.c does not match yours. CCing netdev, hopefully
someone there will know which rcu_dereference() is indicated.

> [ 52.869375] [ INFO: suspicious rcu_dereference_check() usage. ]
> [ 52.869378] ---------------------------------------------------
> [ 52.869382] net/mac80211/sta_info.c:886 invoked
> rcu_dereference_check() without protection!
> [ 52.869386]
> [ 52.869387] other info that might help us debug this:
> [ 52.869389]
> [ 52.869392]
> [ 52.869392] rcu_scheduler_active = 1, debug_locks = 1
> [ 52.869397] 1 lock held by Xorg/4051:
> [ 52.869399] #0: (&dev->struct_mutex){+.+.+.}, at:
> [<ffffffff812afdc4>] i915_gem_do_execbuffer+0xf4c/0xfda
> [ 52.869414]
> [ 52.869415] stack backtrace:
> [ 52.869420] Pid: 4051, comm: Xorg Not tainted 2.6.34-rc5 #18
> [ 52.869423] Call Trace:
> [ 52.869426] <IRQ> [<ffffffff81067fc2>] lockdep_rcu_dereference+0x9d/0xa5
> [ 52.869454] [<ffffffffa01289ae>]
> ieee80211_find_sta_by_hw+0x46/0x10f [mac80211]
> [ 52.869467] [<ffffffffa0128a8e>] ieee80211_find_sta+0x17/0x19 [mac80211]
> [ 52.869483] [<ffffffffa017a0f2>] iwl_tx_queue_reclaim+0xdb/0x1b1 [iwlcore]
> [ 52.869490] [<ffffffff8106842f>] ? mark_lock+0x2d/0x235
> [ 52.869501] [<ffffffffa01a2f1c>] iwl5000_rx_reply_tx+0x4a9/0x556 [iwlagn]
> [ 52.869508] [<ffffffff8120a3d3>] ? is_swiotlb_buffer+0x2e/0x3b
> [ 52.869518] [<ffffffffa019bbf4>] iwl_rx_handle+0x163/0x2b5 [iwlagn]
> [ 52.869524] [<ffffffff81068908>] ? trace_hardirqs_on_caller+0xfa/0x13f
> [ 52.869534] [<ffffffffa019c3ac>] iwl_irq_tasklet+0x2bb/0x3c0 [iwlagn]
> [ 52.869540] [<ffffffff810411df>] tasklet_action+0xa7/0x10f
> [ 52.869546] [<ffffffff810421f1>] __do_softirq+0x144/0x252
> [ 52.869553] [<ffffffff81003a8c>] call_softirq+0x1c/0x34
> [ 52.869559] [<ffffffff810050e4>] do_softirq+0x38/0x80
> [ 52.869564] [<ffffffff81041cbe>] irq_exit+0x45/0x94
> [ 52.869569] [<ffffffff81004829>] do_IRQ+0xad/0xc4
> [ 52.869576] [<ffffffff813cfc13>] ret_from_intr+0x0/0xf
> [ 52.869580] <EOI> [<ffffffff81068765>] ? lockdep_trace_alloc+0xbe/0xc2
> [ 52.869592] [<ffffffff810bca55>] __alloc_pages_nodemask+0x8f/0x6a5
> [ 52.869598] [<ffffffff810b70f5>] ? rcu_read_lock+0x0/0x35
> [ 52.869604] [<ffffffff810b70f5>] ? rcu_read_lock+0x0/0x35
> [ 52.869610] [<ffffffff810c33cb>] ? kmap_atomic+0x16/0x4b
> [ 52.869615] [<ffffffff810b71ad>] ? rcu_read_unlock+0x21/0x23
> [ 52.869621] [<ffffffff810b6c3c>] __page_cache_alloc+0x14/0x16
> [ 52.869627] [<ffffffff810b836d>] do_read_cache_page+0x43/0x121
> [ 52.869632] [<ffffffff810c54bd>] ? shmem_readpage+0x0/0x3c
> [ 52.869638] [<ffffffff810b8464>] read_cache_page_gfp+0x19/0x23
> [ 52.869644] [<ffffffff812aac10>] i915_gem_object_get_pages+0xa1/0x115
> [ 52.869651] [<ffffffff812ad23e>] i915_gem_object_bind_to_gtt+0x16d/0x2ce
> [ 52.869657] [<ffffffff812ad3c6>] i915_gem_object_pin+0x27/0x88
> [ 52.869663] [<ffffffff812af316>] i915_gem_do_execbuffer+0x49e/0xfda
> [ 52.869670] [<ffffffff810cbb93>] ? might_fault+0x63/0xb3
> [ 52.869676] [<ffffffff810cbbdc>] ? might_fault+0xac/0xb3
> [ 52.869681] [<ffffffff810cbb93>] ? might_fault+0x63/0xb3
> [ 52.869687] [<ffffffff812b010d>] i915_gem_execbuffer+0x192/0x221
> [ 52.869694] [<ffffffff812900d0>] drm_ioctl+0x25a/0x36e
> [ 52.869700] [<ffffffff812aff7b>] ? i915_gem_execbuffer+0x0/0x221
> [ 52.869707] [<ffffffff810e9ad1>] ? do_sync_read+0xc6/0x103
> [ 52.869714] [<ffffffff810f6dcd>] vfs_ioctl+0x2d/0xa1
> [ 52.869720] [<ffffffff810f7343>] do_vfs_ioctl+0x48b/0x4d1
> [ 52.869726] [<ffffffff810f73da>] sys_ioctl+0x51/0x74
> [ 52.869733] [<ffffffff81002b6b>] system_call_fastpath+0x16/0x1b

This one looks to be an update-side reference protected by dev->struct_mutex,
but there is no obvious way to get that information to the pair
of rcu_dereference() calls in for_each_sta_info(). Besides which,
I am not 100% certain that this one is really only a false positive.
Especially given that the next one looks similar, but uses a different
lock.

Eric, and enlightenment?

> [ 52.884563] [ INFO: suspicious rcu_dereference_check() usage. ]
> [ 52.884566] ---------------------------------------------------
> [ 52.884571] net/mac80211/sta_info.c:886 invoked
> rcu_dereference_check() without protection!
> [ 52.884574]
> [ 52.884575] other info that might help us debug this:
> [ 52.884577]
> [ 52.884580]
> [ 52.884581] rcu_scheduler_active = 1, debug_locks = 1
> [ 52.884585] 1 lock held by rsyslogd/3854:
> [ 52.884588] #0: (&sb->s_type->i_mutex_key#10){+.+.+.}, at:
> [<ffffffff810b7f97>] generic_file_aio_write+0x47/0xa8
> [ 52.884604]
> [ 52.884605] stack backtrace:
> [ 52.884610] Pid: 3854, comm: rsyslogd Not tainted 2.6.34-rc5 #18
> [ 52.884613] Call Trace:
> [ 52.884617] <IRQ> [<ffffffff81067fc2>] lockdep_rcu_dereference+0x9d/0xa5
> [ 52.884645] [<ffffffffa01289fe>]
> ieee80211_find_sta_by_hw+0x96/0x10f [mac80211]
> [ 52.884658] [<ffffffffa0128a8e>] ieee80211_find_sta+0x17/0x19 [mac80211]
> [ 52.884675] [<ffffffffa017a0f2>] iwl_tx_queue_reclaim+0xdb/0x1b1 [iwlcore]
> [ 52.884681] [<ffffffff8106842f>] ? mark_lock+0x2d/0x235
> [ 52.884693] [<ffffffffa01a2f1c>] iwl5000_rx_reply_tx+0x4a9/0x556 [iwlagn]
> [ 52.884701] [<ffffffff8120a3d3>] ? is_swiotlb_buffer+0x2e/0x3b
> [ 52.884710] [<ffffffffa019bbf4>] iwl_rx_handle+0x163/0x2b5 [iwlagn]
> [ 52.884717] [<ffffffff81068908>] ? trace_hardirqs_on_caller+0xfa/0x13f
> [ 52.884726] [<ffffffffa019c3ac>] iwl_irq_tasklet+0x2bb/0x3c0 [iwlagn]
> [ 52.884733] [<ffffffff810411df>] tasklet_action+0xa7/0x10f
> [ 52.884739] [<ffffffff810421f1>] __do_softirq+0x144/0x252
> [ 52.884746] [<ffffffff81003a8c>] call_softirq+0x1c/0x34
> [ 52.884752] [<ffffffff810050e4>] do_softirq+0x38/0x80
> [ 52.884757] [<ffffffff81041cbe>] irq_exit+0x45/0x94
> [ 52.884762] [<ffffffff81004829>] do_IRQ+0xad/0xc4
> [ 52.884769] [<ffffffff813cfc13>] ret_from_intr+0x0/0xf
> [ 52.884773] <EOI> [<ffffffff810e3509>] ? kmem_cache_free+0xb0/0x134
> [ 52.884789] [<ffffffff811913dc>] ? jbd2_journal_stop+0x32c/0x33e
> [ 52.884796] [<ffffffff811913dc>] jbd2_journal_stop+0x32c/0x33e
> [ 52.884804] [<ffffffff8115e689>] ? ext4_dirty_inode+0x40/0x45
> [ 52.884811] [<ffffffff81105fdb>] ? __mark_inode_dirty+0x2f/0x12e
> [ 52.884819] [<ffffffff81170a65>] __ext4_journal_stop+0x6f/0x75
> [ 52.884825] [<ffffffff81162949>] ext4_da_write_end+0x25c/0x2fc
> [ 52.884833] [<ffffffff810b6b2e>] generic_file_buffered_write+0x161/0x25b
> [ 52.884840] [<ffffffff810b7f1b>] __generic_file_aio_write+0x24a/0x27f
> [ 52.884845] [<ffffffff810b7f97>] ? generic_file_aio_write+0x47/0xa8
> [ 52.884852] [<ffffffff810b7faa>] generic_file_aio_write+0x5a/0xa8
> [ 52.884858] [<ffffffff8115ab2a>] ext4_file_write+0x8c/0x96
> [ 52.884864] [<ffffffff810e99ce>] do_sync_write+0xc6/0x103
> [ 52.884871] [<ffffffff810eac6d>] ? rcu_read_lock+0x0/0x35
> [ 52.884878] [<ffffffff811c17db>] ? selinux_file_permission+0x57/0xaf
> [ 52.884885] [<ffffffff811bb085>] ? security_file_permission+0x11/0x13
> [ 52.884893] [<ffffffff810e9f33>] vfs_write+0xa9/0x106
> [ 52.884898] [<ffffffff810ea046>] sys_write+0x45/0x69
> [ 52.884905] [<ffffffff81002b6b>] system_call_fastpath+0x16/0x1b

Ditto!

> [ 85.939528] [ INFO: suspicious rcu_dereference_check() usage. ]
> [ 85.939531] ---------------------------------------------------
> [ 85.939535] include/net/inet_timewait_sock.h:227 invoked
> rcu_dereference_check() without protection!
> [ 85.939539]
> [ 85.939540] other info that might help us debug this:
> [ 85.939541]
> [ 85.939544]
> [ 85.939545] rcu_scheduler_active = 1, debug_locks = 1
> [ 85.939549] 2 locks held by gwibber-service/4798:
> [ 85.939552] #0: (&p->lock){+.+.+.}, at: [<ffffffff811034b2>]
> seq_read+0x37/0x381
> [ 85.939566] #1: (&(&hashinfo->ehash_locks[i])->rlock){+.-...},
> at: [<ffffffff81386355>] established_get_next+0xc4/0x132
> [ 85.939579]
> [ 85.939580] stack backtrace:
> [ 85.939585] Pid: 4798, comm: gwibber-service Not tainted 2.6.34-rc5 #18
> [ 85.939588] Call Trace:
> [ 85.939598] [<ffffffff81067fc2>] lockdep_rcu_dereference+0x9d/0xa5
> [ 85.939604] [<ffffffff81385018>] twsk_net+0x4f/0x57
> [ 85.939610] [<ffffffff813862e5>] established_get_next+0x54/0x132
> [ 85.939615] [<ffffffff813864c7>] tcp_seq_next+0x5d/0x6a
> [ 85.939621] [<ffffffff81103701>] seq_read+0x286/0x381
> [ 85.939627] [<ffffffff8110347b>] ? seq_read+0x0/0x381
> [ 85.939633] [<ffffffff81133240>] proc_reg_read+0x8d/0xac
> [ 85.939640] [<ffffffff810ea110>] vfs_read+0xa6/0x103
> [ 85.939645] [<ffffffff810ea223>] sys_read+0x45/0x69
> [ 85.939652] [<ffffffff81002b6b>] system_call_fastpath+0x16/0x1b

This one appears to be a case of missing rcu_read_lock(), but it is
not clear to me at what level it needs to go.

Eric, any enlightenment on this one and the next one?

> [ 87.296366] [ INFO: suspicious rcu_dereference_check() usage. ]
> [ 87.296369] ---------------------------------------------------
> [ 87.296373] include/net/inet_timewait_sock.h:227 invoked
> rcu_dereference_check() without protection!
> [ 87.296377]
> [ 87.296377] other info that might help us debug this:
> [ 87.296379]
> [ 87.296382]
> [ 87.296383] rcu_scheduler_active = 1, debug_locks = 1
> [ 87.296386] no locks held by gwibber-service/4803.
> [ 87.296389]
> [ 87.296390] stack backtrace:
> [ 87.296395] Pid: 4803, comm: gwibber-service Not tainted 2.6.34-rc5 #18
> [ 87.296398] Call Trace:
> [ 87.296411] [<ffffffff81067fc2>] lockdep_rcu_dereference+0x9d/0xa5
> [ 87.296419] [<ffffffff813733d3>] twsk_net+0x4f/0x57
> [ 87.296424] [<ffffffff813737f3>] __inet_twsk_hashdance+0x50/0x158
> [ 87.296431] [<ffffffff81389239>] tcp_time_wait+0x1c1/0x24b
> [ 87.296437] [<ffffffff8137c417>] tcp_fin+0x83/0x162
> [ 87.296443] [<ffffffff8137cda7>] tcp_data_queue+0x1ff/0xa1e
> [ 87.296450] [<ffffffff810495c6>] ? mod_timer+0x1e/0x20
> [ 87.296456] [<ffffffff813809e3>] tcp_rcv_state_process+0x89d/0x8f2
> [ 87.296463] [<ffffffff8133ca0b>] ? release_sock+0x30/0x10b
> [ 87.296468] [<ffffffff81386df2>] tcp_v4_do_rcv+0x2de/0x33f
> [ 87.296475] [<ffffffff8133ca5d>] release_sock+0x82/0x10b
> [ 87.296481] [<ffffffff81376ef5>] tcp_close+0x1b5/0x37e
> [ 87.296487] [<ffffffff81395437>] inet_release+0x50/0x57
> [ 87.296493] [<ffffffff8133a134>] sock_release+0x1a/0x66
> [ 87.296498] [<ffffffff8133a1a2>] sock_close+0x22/0x26
> [ 87.296505] [<ffffffff810eb003>] __fput+0x120/0x1cd
> [ 87.296510] [<ffffffff810eb0c5>] fput+0x15/0x17
> [ 87.296516] [<ffffffff810e7f3d>] filp_close+0x63/0x6d
> [ 87.296521] [<ffffffff810e801e>] sys_close+0xd7/0x111
> [ 87.296528] [<ffffffff81002b6b>] system_call_fastpath+0x16/0x1b

commit d3b8ba1bde9afb7d50cf0712f9d95317ea66c06f
Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date: Wed Apr 21 14:04:56 2010 -0700

sched: protect __sched_setscheduler() access to cgroups

A given task's cgroups structures must remain while that task is running
due to reference counting, so this is presumably a false positive.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/sched.c b/kernel/sched.c
index 14c44ec..1d43c1a 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4575,9 +4575,11 @@ recheck:
* Do not allow realtime tasks into groups that have no runtime
* assigned.
*/
+ rcu_read_lock();
if (rt_bandwidth_enabled() && rt_policy(policy) &&
task_group(p)->rt_bandwidth.rt_runtime == 0)
return -EPERM;
+ rcu_read_unlock();
#endif

retval = security_task_setscheduler(p, policy, param);

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