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SubjectRe: [PATCH RT 05/12] slab: Prevent local lock deadlock
On 07/18/12 15:39, Steven Rostedt wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
>
> On RT we avoid the cross cpu function calls and take the per cpu local
> locks instead. Now the code missed that taking the local lock on the
> cpu which runs the code must use the proper local lock functions and
> not a simple spin_lock(). Otherwise it deadlocks later when trying to
> acquire the local lock with the proper function.
>
> Reported-and-tested-by: Chris Pringle <chris.pringle@miranda.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
> mm/slab.c | 26 ++++++++++++++++++++++----
> 1 file changed, 22 insertions(+), 4 deletions(-)


This patch leads to a warning during boot on the ARM pandaboard:

[ 0.225097] Brought up 2 CPUs
[ 0.225097] SMP: Total of 2 processors activated (2007.19 BogoMIPS).
[ 0.225952]
[ 0.225982] =============================================
[ 0.225982] [ INFO: possible recursive locking detected ]
[ 0.225982] 3.0.36-rt58 #1
[ 0.225982] ---------------------------------------------
[ 0.225982] swapper/0/1 is trying to acquire lock:
[ 0.226013] (&per_cpu(slab_lock, __cpu).lock){+.+...}, at: [<c0147544>] do_ccupdate_local+0x18/0x44
[ 0.226043]
[ 0.226043] but task is already holding lock:
[ 0.226043] (&per_cpu(slab_lock, __cpu).lock){+.+...}, at: [<c014737c>] lock_slab_on+0x48/0x134
[ 0.226074]
[ 0.226074] other info that might help us debug this:
[ 0.226074] Possible unsafe locking scenario:
[ 0.226074]
[ 0.226074] CPU0
[ 0.226074] ----
[ 0.226074] lock(&per_cpu(slab_lock, __cpu).lock);
[ 0.226104] lock(&per_cpu(slab_lock, __cpu).lock);
[ 0.226104]
[ 0.226104] *** DEADLOCK ***
[ 0.226104]
[ 0.226104] May be due to missing lock nesting notation
[ 0.226104]
[ 0.226104] 2 locks held by swapper/0/1:
[ 0.226135] #0: (cache_chain_mutex){+.+.+.}, at: [<c014a618>] kmem_cache_create+0x74/0x4bc
[ 0.226135] #1: (&per_cpu(slab_lock, __cpu).lock){+.+...}, at: [<c014737c>] lock_slab_on+0x48/0x134
[ 0.226165]
[ 0.226165] stack backtrace:
[ 0.226196] [<c00681f8>] (unwind_backtrace+0x0/0xf0) from [<c00da918>] (__lock_acquire+0x1984/0x1ce8)
[ 0.226196] [<c00da918>] (__lock_acquire+0x1984/0x1ce8) from [<c00db29c>] (lock_acquire+0x100/0x120)
[ 0.226226] [<c00db29c>] (lock_acquire+0x100/0x120) from [<c0485c10>] (rt_spin_lock+0x4c/0x5c)
[ 0.226257] [<c0485c10>] (rt_spin_lock+0x4c/0x5c) from [<c0147544>] (do_ccupdate_local+0x18/0x44)
[ 0.226257] [<c0147544>] (do_ccupdate_local+0x18/0x44) from [<c01476e8>] (slab_on_each_cpu+0x2c/0x64)
[ 0.226287] [<c01476e8>] (slab_on_each_cpu+0x2c/0x64) from [<c0149c70>] (do_tune_cpucache+0xd8/0x3e8)
[ 0.226287] [<c0149c70>] (do_tune_cpucache+0xd8/0x3e8) from [<c014a154>] (enable_cpucache+0x50/0xcc)
[ 0.226318] [<c014a154>] (enable_cpucache+0x50/0xcc) from [<c014a974>] (kmem_cache_create+0x3d0/0x4bc)
[ 0.226318] [<c014a974>] (kmem_cache_create+0x3d0/0x4bc) from [<c0021e54>] (init_tmpfs+0x3c/0xe8)
[ 0.226348] [<c0021e54>] (init_tmpfs+0x3c/0xe8) from [<c00083b4>] (kernel_init+0x80/0x150)
[ 0.226379] [<c00083b4>] (kernel_init+0x80/0x150) from [<c0061e30>] (kernel_thread_exit+0x0/0x8)
[ 0.239776] omap_hwmod: _populate_mpu_rt_base found no _mpu_rt_va for emif_fw
[ 0.239776] omap_hwmod: _populate_mpu_rt_base found no _mpu_rt_va for l3_instr



Config is from arch/arm/configs/omap2plus_defconfig
plus:

CONFIG_USB_EHCI_HCD=y
CONFIG_USB_NET_SMSC95XX=y
CONFIG_PREEMPT_RT_FULL=y


-Frank



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