The following warning triggers with a new unit test that stresses the device-dax interface. =============================== [ ERR: suspicious RCU usage. ] 4.11.0-rc4+ #1049 Tainted: G O ------------------------------- ./include/linux/rcupdate.h:521 Illegal context switch in RCU read-side critical section! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 0 2 locks held by fio/9070: #0: (&mm->mmap_sem){++++++}, at: [<ffffffff8d0739d7>] __do_page_fault+0x167/0x4f0 #1: (rcu_read_lock){......}, at: [<ffffffffc03fbd02>] dax_dev_huge_fault+0x32/0x620 [dax] Call Trace: dump_stack+0x86/0xc3 lockdep_rcu_suspicious+0xd7/0x110 ___might_sleep+0xac/0x250 __might_sleep+0x4a/0x80 __alloc_pages_nodemask+0x23a/0x360 alloc_pages_current+0xa1/0x1f0 pte_alloc_one+0x17/0x80 __pte_alloc+0x1e/0x120 __get_locked_pte+0x1bf/0x1d0 insert_pfn.isra.70+0x3a/0x100 ? lookup_memtype+0xa6/0xd0 vm_insert_mixed+0x64/0x90 dax_dev_huge_fault+0x520/0x620 [dax] ? dax_dev_huge_fault+0x32/0x620 [dax] dax_dev_fault+0x10/0x20 [dax] __do_fault+0x1e/0x140 __handle_mm_fault+0x9af/0x10d0 handle_mm_fault+0x16d/0x370 ? handle_mm_fault+0x47/0x370 __do_page_fault+0x28c/0x4f0 trace_do_page_fault+0x58/0x2a0 do_async_page_fault+0x1a/0xa0 async_page_fault+0x28/0x30 Inserting a page table entry may trigger an allocation while we are holding a read lock to keep the device instance alive for the duration of the fault. Use srcu for this keep-alive protection. Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap") Cc: <stable(a)vger.kernel.org&gt; Signed-off-by: Dan Williams <dan.j.williams(a)intel.com&gt; --- drivers/dax/Kconfig | 1 + drivers/dax/dax.c | 13 +++++++------ 2 files changed, 8 insertions(+), 6 deletions(-) diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig index 3e2ab3b14eea..9e95bf94eb13 100644 --- a/drivers/dax/Kconfig +++ b/drivers/dax/Kconfig @@ -2,6 +2,7 @@ menuconfig DEV_DAX tristate "DAX: direct access to differentiated memory" default m if NVDIMM_DAX depends on TRANSPARENT_HUGEPAGE + select SRCU help Support raw access to differentiated (persistence, bandwidth, latency...) memory via an mmap(2) capable character diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c index 80c6db279ae1..806f180c80d8 100644 --- a/drivers/dax/dax.c +++ b/drivers/dax/dax.c @@ -25,6 +25,7 @@ #include "dax.h" static dev_t dax_devt; +DEFINE_STATIC_SRCU(dax_srcu); static struct class *dax_class; static DEFINE_IDA(dax_minor_ida); static int nr_dax = CONFIG_NR_DEV_DAX; @@ -60,7 +61,7 @@ struct dax_region { * @region - parent region * @dev - device backing the character device * @cdev - core chardev data - * @alive - !alive + rcu grace period == no new mappings can be established + * @alive - !alive + srcu grace period == no new mappings can be established * @id - child id in the region * @num_resources - number of physical address extents in this device * @res - array of physical address ranges @@ -569,7 +570,7 @@ static int __dax_dev_pud_fault(struct dax_dev *dax_dev, struct vm_fault *vmf) static int dax_dev_huge_fault(struct vm_fault *vmf, enum page_entry_size pe_size) { - int rc; + int rc, id; struct file *filp = vmf->vma->vm_file; struct dax_dev *dax_dev = filp->private_data; @@ -578,7 +579,7 @@ static int dax_dev_huge_fault(struct vm_fault *vmf, ? "write" : "read", vmf->vma->vm_start, vmf->vma->vm_end); - rcu_read_lock(); + id = srcu_read_lock(&dax_srcu); switch (pe_size) { case PE_SIZE_PTE: rc = __dax_dev_pte_fault(dax_dev, vmf); @@ -592,7 +593,7 @@ static int dax_dev_huge_fault(struct vm_fault *vmf, default: return VM_FAULT_FALLBACK; } - rcu_read_unlock(); + srcu_read_unlock(&dax_srcu, id); return rc; } @@ -713,11 +714,11 @@ static void unregister_dax_dev(void *dev) * Note, rcu is not protecting the liveness of dax_dev, rcu is * ensuring that any fault handlers that might have seen * dax_dev->alive == true, have completed. Any fault handlers - * that start after synchronize_rcu() has started will abort + * that start after synchronize_srcu() has started will abort * upon seeing dax_dev->alive == false. */ dax_dev->alive = false; - synchronize_rcu(); + synchronize_srcu(&dax_srcu); unmap_mapping_range(dax_dev->inode->i_mapping, 0, 0, 1); cdev_del(cdev); device_unregister(dev);