Between acquiring the this_cpu_ptr() and using it, ideally we don't want to be preempted and work on another CPU's private data. If we disable preemption around this_cpu_ptr, we do not need the CPU local spinlock - so long as take care that no other CPU is running that code as do perform the cross-CPU cache flushing and teardown.
[ 167.997877] BUG: using smp_processor_id() in preemptible [00000000] code: usb-storage/216 [ 167.997940] caller is debug_smp_processor_id+0x17/0x20 [ 167.997945] CPU: 7 PID: 216 Comm: usb-storage Tainted: G U 4.7.0-rc1-gfxbench-RO_Patchwork_1057+ #1 [ 167.997948] Hardware name: Hewlett-Packard HP Pro 3500 Series/2ABF, BIOS 8.11 10/24/2012 [ 167.997951] 0000000000000000 ffff880118b7f9c8 ffffffff8140dca5 0000000000000007 [ 167.997958] ffffffff81a3a7e9 ffff880118b7f9f8 ffffffff8142a927 0000000000000000 [ 167.997965] ffff8800d499ed58 0000000000000001 00000000000fffff ffff880118b7fa08 [ 167.997971] Call Trace: [ 167.997977] [<ffffffff8140dca5>] dump_stack+0x67/0x92 [ 167.997981] [<ffffffff8142a927>] check_preemption_disabled+0xd7/0xe0 [ 167.997985] [<ffffffff8142a947>] debug_smp_processor_id+0x17/0x20 [ 167.997990] [<ffffffff81507e17>] alloc_iova_fast+0xb7/0x210 [ 167.997994] [<ffffffff8150c55f>] intel_alloc_iova+0x7f/0xd0 [ 167.997998] [<ffffffff8151021d>] intel_map_sg+0xbd/0x240 [ 167.998002] [<ffffffff810e5efd>] ? debug_lockdep_rcu_enabled+0x1d/0x20 [ 167.998009] [<ffffffff81596059>] usb_hcd_map_urb_for_dma+0x4b9/0x5a0 [ 167.998013] [<ffffffff81596d19>] usb_hcd_submit_urb+0xe9/0xaa0 [ 167.998017] [<ffffffff810cff2f>] ? mark_held_locks+0x6f/0xa0 [ 167.998022] [<ffffffff810d525c>] ? __raw_spin_lock_init+0x1c/0x50 [ 167.998025] [<ffffffff810e5efd>] ? debug_lockdep_rcu_enabled+0x1d/0x20 [ 167.998028] [<ffffffff815988f3>] usb_submit_urb+0x3f3/0x5a0 [ 167.998032] [<ffffffff810d0082>] ? trace_hardirqs_on_caller+0x122/0x1b0 [ 167.998035] [<ffffffff81599ae7>] usb_sg_wait+0x67/0x150 [ 167.998039] [<ffffffff815dc202>] usb_stor_bulk_transfer_sglist.part.3+0x82/0xd0 [ 167.998042] [<ffffffff815dc29c>] usb_stor_bulk_srb+0x4c/0x60 [ 167.998045] [<ffffffff815dc42e>] usb_stor_Bulk_transport+0x17e/0x420 [ 167.998049] [<ffffffff815dcf32>] usb_stor_invoke_transport+0x242/0x540 [ 167.998052] [<ffffffff810e5efd>] ? debug_lockdep_rcu_enabled+0x1d/0x20 [ 167.998058] [<ffffffff815dba19>] usb_stor_transparent_scsi_command+0x9/0x10 [ 167.998061] [<ffffffff815de518>] usb_stor_control_thread+0x158/0x260 [ 167.998064] [<ffffffff815de3c0>] ? fill_inquiry_response+0x20/0x20 [ 167.998067] [<ffffffff815de3c0>] ? fill_inquiry_response+0x20/0x20 [ 167.998071] [<ffffffff8109ddfa>] kthread+0xea/0x100 [ 167.998078] [<ffffffff817ac6af>] ret_from_fork+0x1f/0x40 [ 167.998081] [<ffffffff8109dd10>] ? kthread_create_on_node+0x1f0/0x1f0 Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96293 Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com> Cc: Joerg Roedel <j...@8bytes.org> Cc: io...@lists.linux-foundation.org Cc: linux-kernel@vger.kernel.org --- drivers/iommu/iova.c | 31 ++++++++++--------------------- 1 file changed, 10 insertions(+), 21 deletions(-) diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c index ba764a0835d3..5c5bbdb86a42 100644 --- a/drivers/iommu/iova.c +++ b/drivers/iommu/iova.c @@ -390,6 +390,11 @@ free_iova(struct iova_domain *iovad, unsigned long pfn) } EXPORT_SYMBOL_GPL(free_iova); +static void free_this_cached_iovas(void *info) +{ + free_cpu_cached_iovas(smp_processor_id(), info); +} + /** * alloc_iova_fast - allocates an iova from rcache * @iovad: - iova domain in question @@ -413,15 +418,12 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size, retry: new_iova = alloc_iova(iovad, size, limit_pfn, true); if (!new_iova) { - unsigned int cpu; - if (flushed_rcache) return 0; /* Try replenishing IOVAs by flushing rcache. */ flushed_rcache = true; - for_each_online_cpu(cpu) - free_cpu_cached_iovas(cpu, iovad); + on_each_cpu(free_this_cached_iovas, iovad, true); goto retry; } @@ -645,7 +647,6 @@ struct iova_magazine { }; struct iova_cpu_rcache { - spinlock_t lock; struct iova_magazine *loaded; struct iova_magazine *prev; }; @@ -727,7 +728,6 @@ static void init_iova_rcaches(struct iova_domain *iovad) continue; for_each_possible_cpu(cpu) { cpu_rcache = per_cpu_ptr(rcache->cpu_rcaches, cpu); - spin_lock_init(&cpu_rcache->lock); cpu_rcache->loaded = iova_magazine_alloc(GFP_KERNEL); cpu_rcache->prev = iova_magazine_alloc(GFP_KERNEL); } @@ -747,10 +747,9 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, struct iova_magazine *mag_to_free = NULL; struct iova_cpu_rcache *cpu_rcache; bool can_insert = false; - unsigned long flags; + preempt_disable(); cpu_rcache = this_cpu_ptr(rcache->cpu_rcaches); - spin_lock_irqsave(&cpu_rcache->lock, flags); if (!iova_magazine_full(cpu_rcache->loaded)) { can_insert = true; @@ -778,7 +777,7 @@ static bool __iova_rcache_insert(struct iova_domain *iovad, if (can_insert) iova_magazine_push(cpu_rcache->loaded, iova_pfn); - spin_unlock_irqrestore(&cpu_rcache->lock, flags); + preempt_enable(); if (mag_to_free) { iova_magazine_free_pfns(mag_to_free, iovad); @@ -810,10 +809,9 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache, struct iova_cpu_rcache *cpu_rcache; unsigned long iova_pfn = 0; bool has_pfn = false; - unsigned long flags; + preempt_disable(); cpu_rcache = this_cpu_ptr(rcache->cpu_rcaches); - spin_lock_irqsave(&cpu_rcache->lock, flags); if (!iova_magazine_empty(cpu_rcache->loaded)) { has_pfn = true; @@ -833,7 +831,7 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache, if (has_pfn) iova_pfn = iova_magazine_pop(cpu_rcache->loaded, limit_pfn); - spin_unlock_irqrestore(&cpu_rcache->lock, flags); + preempt_enable(); return iova_pfn; } @@ -862,17 +860,11 @@ static void free_cpu_iova_rcache(unsigned int cpu, struct iova_domain *iovad, struct iova_rcache *rcache) { struct iova_cpu_rcache *cpu_rcache = per_cpu_ptr(rcache->cpu_rcaches, cpu); - unsigned long flags; - - spin_lock_irqsave(&cpu_rcache->lock, flags); - iova_magazine_free_pfns(cpu_rcache->loaded, iovad); iova_magazine_free(cpu_rcache->loaded); iova_magazine_free_pfns(cpu_rcache->prev, iovad); iova_magazine_free(cpu_rcache->prev); - - spin_unlock_irqrestore(&cpu_rcache->lock, flags); } /* @@ -906,16 +898,13 @@ void free_cpu_cached_iovas(unsigned int cpu, struct iova_domain *iovad) { struct iova_cpu_rcache *cpu_rcache; struct iova_rcache *rcache; - unsigned long flags; int i; for (i = 0; i < IOVA_RANGE_CACHE_MAX_SIZE; ++i) { rcache = &iovad->rcaches[i]; cpu_rcache = per_cpu_ptr(rcache->cpu_rcaches, cpu); - spin_lock_irqsave(&cpu_rcache->lock, flags); iova_magazine_free_pfns(cpu_rcache->loaded, iovad); iova_magazine_free_pfns(cpu_rcache->prev, iovad); - spin_unlock_irqrestore(&cpu_rcache->lock, flags); } } -- 2.8.1
