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device-dax: switch to srcu, fix rcu_read_lock() vs pte allocation

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commit 956a4cd2c957acf638ff29951aabaa9d8e92bbc2 upstream.

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")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Dan Williams 2017-04-07 16:42:08 -07:00 committed by Greg Kroah-Hartman
parent f8bc0881fe
commit c36eaa6ca3
2 changed files with 8 additions and 6 deletions
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1
drivers/dax/Kconfig
View File

@ -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

13
drivers/dax/dax.c
View File

@ -24,6 +24,7 @@
#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;
@ -59,7 +60,7 @@ 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
@ -437,7 +438,7 @@ static int __dax_dev_pmd_fault(struct dax_dev *dax_dev,
static int dax_dev_pmd_fault(struct vm_area_struct *vma, unsigned long addr,
pmd_t *pmd, unsigned int flags)
{
int rc;
int rc, id;
struct file *filp = vma->vm_file;
struct dax_dev *dax_dev = filp->private_data;
@ -445,9 +446,9 @@ static int dax_dev_pmd_fault(struct vm_area_struct *vma, unsigned long addr,
current->comm, (flags & FAULT_FLAG_WRITE)
? "write" : "read", vma->vm_start, vma->vm_end);
rcu_read_lock();
id = srcu_read_lock(&dax_srcu);
rc = __dax_dev_pmd_fault(dax_dev, vma, addr, pmd, flags);
rcu_read_unlock();
srcu_read_unlock(&dax_srcu, id);
return rc;
}
@ -563,11 +564,11 @@ 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);