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        Tue, 13 Dec 2016 04:59:51 -0500
From: Kalle Valo <kvalo@codeaurora.org>
To: Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
Cc: helgaas@kernel.org, linux-kernel@vger.kernel.org,
        linux-pci@vger.kernel.org, marc.zyngier@arm.com,
        Janusz.Dziedzic@tieto.com, rmanohar@qti.qualcomm.com,
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        rmanohar@qca.qualcomm.com, bharat.kumar.gogada@xilinx.com,
        Felix Fietkau <nbd@nbd.name>
Subject: Re: [PATCH] ath9k: unlock rcu read when returning early
References: <20161212185001.3857-1-tobias.johannes.klausmann@mni.thm.de>
Date: Tue, 13 Dec 2016 11:59:42 +0200
In-Reply-To: <20161212185001.3857-1-tobias.johannes.klausmann@mni.thm.de>
        (Tobias Klausmann's message of "Mon, 12 Dec 2016 19:50:01 +0100")
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Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de> writes:

> Starting with ath9k: use ieee80211_tx_status_noskb where possible
> [d94a461d7a7df68991fb9663531173f60ef89c68]

The correct format to reference a commit in the commit log is:

Starting with commit d94a461d7a7d ("ath9k: use ieee80211_tx_status_noskb
where possible") the...

> the driver uses rcu_read_lock() && rcu_read_unlock() yet on returning
> early in ath_tx_edma_tasklet() the unlock is missing leading to stalls
> and suspicious RCU usage:
>
>  ===============================
>  [ INFO: suspicious RCU usage. ]
>  4.9.0-rc8 #11 Not tainted
>  -------------------------------
>  kernel/rcu/tree.c:705 Illegal idle entry in RCU read-side critical section.!
>
>  other info that might help us debug this:
>
>  RCU used illegally from idle CPU!
>  rcu_scheduler_active = 1, debug_locks = 0
>  RCU used illegally from extended quiescent state!
>  1 lock held by swapper/7/0:
>  #0:
>   (
>  rcu_read_lock
>  ){......}
>  , at:
>  [<ffffffffa06ed110>] ath_tx_edma_tasklet+0x0/0x450 [ath9k]
>
>  stack backtrace:
>  CPU: 7 PID: 0 Comm: swapper/7 Not tainted 4.9.0-rc8 #11
>  Hardware name: Acer Aspire V3-571G/VA50_HC_CR, BIOS V2.21 12/16/2013
>   ffff88025efc3f38 ffffffff8132b1e5 ffff88017ede4540 0000000000000001
>   ffff88025efc3f68 ffffffff810a25f7 ffff88025efcee60 ffff88017edebdd8
>   ffff88025eeb5400 0000000000000091 ffff88025efc3f88 ffffffff810c3cd4
>  Call Trace:
>   <IRQ>
>   [<ffffffff8132b1e5>] dump_stack+0x68/0x93
>   [<ffffffff810a25f7>] lockdep_rcu_suspicious+0xd7/0x110
>   [<ffffffff810c3cd4>] rcu_eqs_enter_common.constprop.85+0x154/0x200
>   [<ffffffff810c5a54>] rcu_irq_exit+0x44/0xa0
>   [<ffffffff81058631>] irq_exit+0x61/0xd0
>   [<ffffffff81018d25>] do_IRQ+0x65/0x110
>   [<ffffffff81672189>] common_interrupt+0x89/0x89
>   <EOI>
>   [<ffffffff814ffe11>] ? cpuidle_enter_state+0x151/0x200
>   [<ffffffff814ffee2>] cpuidle_enter+0x12/0x20
>   [<ffffffff8109a6ae>] call_cpuidle+0x1e/0x40
>   [<ffffffff8109a8f6>] cpu_startup_entry+0x146/0x220
>   [<ffffffff810336f8>] start_secondary+0x148/0x170
>
> Signed-off-by: Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de>

A fixes line and cc stable would be good to have:

Fixes: d94a461d7a7d ("ath9k: use ieee80211_tx_status_noskb where possible")
Cc: <stable@vger.kernel.org> # v4.9

I can add those.

I'm planning to push this to 4.10 but would prefer to see an ack from
Felix (the author of d94a461d7a7d) first. I added him to Cc.

-- 
Kalle Valo