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Mon, 12 Oct 2020 12:45:33 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1602467138; bh=QMZkogI/gfDoyPHm/Lw5pjXwd5LTspyIiIIxRsHsUhE=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=G2SILhc5zkJv94KDxb2kWB4/qyoGwraRecRHH+4IQoyIvFEaqLhtooHgvfyzzuZFl YPzWUvHFRZjWnq1p1acv2p2D2YbjTyAUNMFR4dAEuVcXaxgVmIhpeIb9mzH9gwkLOg CHCnaovOIHeORhIoMTGfpSQTRcwjmYcm/3NQPYBgEjT33tl/8LxYGXrDI8kpbjmQMq 9bQiWKxfSPNGHzMZNRC27yLVwkYbcNr1BZAo8z3LRmRTEZv8wGMlCy18gVmp3TpRwu DxUjK2O/IPbDNOvuqm5k2QTF8awhYHFfcM13Ag5PYgQr+XefpUFtjhDs38pcQFyTlR sBDe+EGxPLyfg== From: Michael Ellerman To: Srikar Dronamraju Subject: Re: [PATCH] powerpc/smp: Use GFP_ATOMIC while allocating tmp mask In-Reply-To: <20201008034240.34059-1-srikar@linux.vnet.ibm.com> References: <20201008034240.34059-1-srikar@linux.vnet.ibm.com> Date: Mon, 12 Oct 2020 12:45:33 +1100 Message-ID: <874kn01aki.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Nathan Lynch , Gautham R Shenoy , Srikar Dronamraju , Qian Cai , LKML , Valentin Schneider , Peter Zijlstra , linuxppc-dev , Ingo Molnar Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Srikar Dronamraju writes: > Qian Cai reported a regression where CPU Hotplug fails with the latest > powerpc/next > > BUG: sleeping function called from invalid context at mm/slab.h:494 > in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 0, name: swapper/88 > no locks held by swapper/88/0. > irq event stamp: 18074448 > hardirqs last enabled at (18074447): [] tick_nohz_idle_enter+0x9c/0x110 > hardirqs last disabled at (18074448): [] do_idle+0x138/0x3b0 > do_idle at kernel/sched/idle.c:253 (discriminator 1) > softirqs last enabled at (18074440): [] irq_enter_rcu+0x94/0xa0 > softirqs last disabled at (18074439): [] irq_enter_rcu+0x70/0xa0 > CPU: 88 PID: 0 Comm: swapper/88 Tainted: G W 5.9.0-rc8-next-20201007 #1 > Call Trace: > [c00020000a4bfcf0] [c000000000649e98] dump_stack+0xec/0x144 (unreliable) > [c00020000a4bfd30] [c0000000000f6c34] ___might_sleep+0x2f4/0x310 > [c00020000a4bfdb0] [c000000000354f94] slab_pre_alloc_hook.constprop.82+0x124/0x190 > [c00020000a4bfe00] [c00000000035e9e8] __kmalloc_node+0x88/0x3a0 > slab_alloc_node at mm/slub.c:2817 > (inlined by) __kmalloc_node at mm/slub.c:4013 > [c00020000a4bfe80] [c0000000006494d8] alloc_cpumask_var_node+0x38/0x80 > kmalloc_node at include/linux/slab.h:577 > (inlined by) alloc_cpumask_var_node at lib/cpumask.c:116 > [c00020000a4bfef0] [c00000000003eedc] start_secondary+0x27c/0x800 > update_mask_by_l2 at arch/powerpc/kernel/smp.c:1267 > (inlined by) add_cpu_to_masks at arch/powerpc/kernel/smp.c:1387 > (inlined by) start_secondary at arch/powerpc/kernel/smp.c:1420 > [c00020000a4bff90] [c00000000000c468] start_secondary_resume+0x10/0x14 > > Allocating a temporary mask while performing a CPU Hotplug operation > with CONFIG_CPUMASK_OFFSTACK enabled, leads to calling a sleepable > function from a atomic context. Fix this by allocating the temporary > mask with GFP_ATOMIC flag. > > If there is a failure to allocate a mask, scheduler is going to observe > that this CPU's topology is broken. Instead of having to speculate why > the topology is broken, add a WARN_ON_ONCE. > > Fixes: 70a94089d7f7 ("powerpc/smp: Optimize update_coregroup_mask") > Fixes: 3ab33d6dc3e9 ("powerpc/smp: Optimize update_mask_by_l2") > Reported-by: Qian Cai > Suggested-by: Qian Cai > Signed-off-by: Srikar Dronamraju > Cc: linuxppc-dev > Cc: LKML > Cc: Michael Ellerman > Cc: Nathan Lynch > Cc: Gautham R Shenoy > Cc: Ingo Molnar > Cc: Peter Zijlstra > Cc: Valentin Schneider > Cc: Qian Cai > --- > arch/powerpc/kernel/smp.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c > index 0dc1b85..1268558 100644 > --- a/arch/powerpc/kernel/smp.c > +++ b/arch/powerpc/kernel/smp.c > @@ -1264,7 +1264,8 @@ static bool update_mask_by_l2(int cpu) > return false; > } > > - alloc_cpumask_var_node(&mask, GFP_KERNEL, cpu_to_node(cpu)); > + /* In CPU-hotplug path, hence use GFP_ATOMIC */ > + WARN_ON_ONCE(!alloc_cpumask_var_node(&mask, GFP_ATOMIC, cpu_to_node(cpu))); A failed memory allocation is not something that should trigger a WARN, a pr_warn() maybe. But ... > cpumask_and(mask, cpu_online_mask, cpu_cpu_mask(cpu)); If the allocation failed this will oops (mask will be NULL). cheers