On Wed, Mar 17, 2021 at 09:08:23PM -0700, Dan Williams wrote: > Jason wondered why the get_user_pages_fast() path takes references on a > @pgmap object. The rationale was to protect against accessing a 'struct > page' that might be in the process of being removed by the driver, but > he rightly points out that should be solved the same way all gup-fast > synchronization is solved which is invalidate the mapping and let the > gup slow path do @pgmap synchronization [1]. > > To achieve that it means that new user mappings need to stop being > created and all existing user mappings need to be invalidated. > > For device-dax this is already the case as kill_dax() prevents future > faults from installing a pte, and the single device-dax inode > address_space can be trivially unmapped. > > The situation is different for filesystem-dax where device pages could > be mapped by any number of inode address_space instances. An initial > thought was to treat the device removal event like a drop_pagecache_sb() > event that walks superblocks and unmaps all inodes. However, Dave points > out that it is not just the filesystem user-mappings that need to react > to global DAX page-unmap events, it is also filesystem metadata > (proposed DAX metadata access), and other drivers (upstream > DM-writecache) that need to react to this event [2]. > > The only kernel facility that is meant to globally broadcast the loss of > a page (via corruption or surprise remove) is memory_failure(). The > downside of memory_failure() is that it is a pfn-at-a-time interface. > However, the events that would trigger the need to call memory_failure() > over a full PMEM device should be rare. Remove should always be > coordinated by the administrator with the filesystem. If someone force > removes a device from underneath a mounted filesystem the driver assumes > they have a good reason, or otherwise get to keep the pieces. Since > ->remove() callbacks can not fail the only option is to trigger the mass > memory_failure(). > > The mechanism to determine whether memory_failure() triggers at > pmem->remove() time is whether the associated dax_device has an elevated > reference at @pgmap ->kill() time. > > With this in place the get_user_pages_fast() path can drop its > half-measure synchronization with an @pgmap reference. > > Link: http://lore.kernel.org/r/20210224010017.GQ2643399@xxxxxxxx [1] > Link: http://lore.kernel.org/r/20210302075736.GJ4662@xxxxxxxxxxxxxxxxxxx [2] > Reported-by: Jason Gunthorpe <jgg@xxxxxxxx> > Cc: Dave Chinner <david@xxxxxxxxxxxxx> > Cc: Christoph Hellwig <hch@xxxxxx> > Cc: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx> > Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx> > Cc: Dave Jiang <dave.jiang@xxxxxxxxx> > Cc: Ira Weiny <ira.weiny@xxxxxxxxx> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > Cc: Jan Kara <jack@xxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx> > Cc: "Darrick J. Wong" <djwong@xxxxxxxxxx> > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> > --- > drivers/dax/super.c | 15 +++++++++++++++ > drivers/nvdimm/pmem.c | 10 +++++++++- > drivers/nvdimm/pmem.h | 1 + > include/linux/dax.h | 5 +++++ > include/linux/memremap.h | 5 +++++ > include/linux/mm.h | 3 +++ > mm/memory-failure.c | 11 +++++++++-- > mm/memremap.c | 11 +++++++++++ > 8 files changed, 58 insertions(+), 3 deletions(-) > > diff --git a/drivers/dax/super.c b/drivers/dax/super.c > index 5fa6ae9dbc8b..5ebcedf4a68c 100644 > --- a/drivers/dax/super.c > +++ b/drivers/dax/super.c > @@ -624,6 +624,21 @@ void put_dax(struct dax_device *dax_dev) > } > EXPORT_SYMBOL_GPL(put_dax); > > +bool dax_is_idle(struct dax_device *dax_dev) > +{ > + struct inode *inode; > + > + if (!dax_dev) > + return true; > + > + WARN_ONCE(test_bit(DAXDEV_ALIVE, &dax_dev->flags), > + "dax idle check on live device.\n"); > + > + inode = &dax_dev->inode; > + return atomic_read(&inode->i_count) < 2; > +} > +EXPORT_SYMBOL_GPL(dax_is_idle); > + > /** > * dax_get_by_host() - temporary lookup mechanism for filesystem-dax > * @host: alternate name for the device registered by a dax driver > diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c > index b8a85bfb2e95..e8822c9262ee 100644 > --- a/drivers/nvdimm/pmem.c > +++ b/drivers/nvdimm/pmem.c > @@ -348,15 +348,21 @@ static void pmem_pagemap_kill(struct dev_pagemap *pgmap) > { > struct request_queue *q = > container_of(pgmap->ref, struct request_queue, q_usage_counter); > + struct pmem_device *pmem = q->queuedata; > > blk_freeze_queue_start(q); > + kill_dax(pmem->dax_dev); > + if (!dax_is_idle(pmem->dax_dev)) { > + dev_warn(pmem->dev, > + "DAX active at remove, trigger mass memory failure\n"); > + dev_pagemap_failure(pgmap); > + } > } > > static void pmem_release_disk(void *__pmem) > { > struct pmem_device *pmem = __pmem; > > - kill_dax(pmem->dax_dev); > put_dax(pmem->dax_dev); > del_gendisk(pmem->disk); > put_disk(pmem->disk); > @@ -406,6 +412,7 @@ static int pmem_attach_disk(struct device *dev, > devm_namespace_disable(dev, ndns); > > dev_set_drvdata(dev, pmem); > + pmem->dev = dev; > pmem->phys_addr = res->start; > pmem->size = resource_size(res); > fua = nvdimm_has_flush(nd_region); > @@ -467,6 +474,7 @@ static int pmem_attach_disk(struct device *dev, > blk_queue_flag_set(QUEUE_FLAG_NONROT, q); > if (pmem->pfn_flags & PFN_MAP) > blk_queue_flag_set(QUEUE_FLAG_DAX, q); > + q->queuedata = pmem; > > disk = alloc_disk_node(0, nid); > if (!disk) > diff --git a/drivers/nvdimm/pmem.h b/drivers/nvdimm/pmem.h > index 59cfe13ea8a8..1222088a569a 100644 > --- a/drivers/nvdimm/pmem.h > +++ b/drivers/nvdimm/pmem.h > @@ -23,6 +23,7 @@ struct pmem_device { > struct badblocks bb; > struct dax_device *dax_dev; > struct gendisk *disk; > + struct device *dev; > struct dev_pagemap pgmap; > }; > > diff --git a/include/linux/dax.h b/include/linux/dax.h > index b52f084aa643..015f1d9a8232 100644 > --- a/include/linux/dax.h > +++ b/include/linux/dax.h > @@ -46,6 +46,7 @@ struct dax_device *alloc_dax(void *private, const char *host, > const struct dax_operations *ops, unsigned long flags); > void put_dax(struct dax_device *dax_dev); > void kill_dax(struct dax_device *dax_dev); > +bool dax_is_idle(struct dax_device *dax_dev); > void dax_write_cache(struct dax_device *dax_dev, bool wc); > bool dax_write_cache_enabled(struct dax_device *dax_dev); > bool __dax_synchronous(struct dax_device *dax_dev); > @@ -92,6 +93,10 @@ static inline void put_dax(struct dax_device *dax_dev) > static inline void kill_dax(struct dax_device *dax_dev) > { > } > +static inline bool dax_is_idle(struct dax_device *dax_dev) > +{ > + return true; > +} > static inline void dax_write_cache(struct dax_device *dax_dev, bool wc) > { > } > diff --git a/include/linux/memremap.h b/include/linux/memremap.h > index f5b464daeeca..d52cdc6c5313 100644 > --- a/include/linux/memremap.h > +++ b/include/linux/memremap.h > @@ -137,6 +137,7 @@ void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap); > void devm_memunmap_pages(struct device *dev, struct dev_pagemap *pgmap); > struct dev_pagemap *get_dev_pagemap(unsigned long pfn, > struct dev_pagemap *pgmap); > +void dev_pagemap_failure(struct dev_pagemap *pgmap); > bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn); > > unsigned long vmem_altmap_offset(struct vmem_altmap *altmap); > @@ -160,6 +161,10 @@ static inline void devm_memunmap_pages(struct device *dev, > { > } > > +static inline void dev_pagemap_failure(struct dev_pagemap *pgmap) > +{ > +} > + > static inline struct dev_pagemap *get_dev_pagemap(unsigned long pfn, > struct dev_pagemap *pgmap) > { > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 77e64e3eac80..95f79f457bab 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -3002,8 +3002,11 @@ enum mf_flags { > MF_ACTION_REQUIRED = 1 << 1, > MF_MUST_KILL = 1 << 2, > MF_SOFT_OFFLINE = 1 << 3, > + MF_MEM_REMOVE = 1 << 4, > }; > extern int memory_failure(unsigned long pfn, int flags); > +extern int memory_failure_dev_pagemap(unsigned long pfn, int flags, > + struct dev_pagemap *pgmap); > extern void memory_failure_queue(unsigned long pfn, int flags); > extern void memory_failure_queue_kick(int cpu); > extern int unpoison_memory(unsigned long pfn); > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > index 43ba4307c526..8f557beb19ee 100644 > --- a/mm/memory-failure.c > +++ b/mm/memory-failure.c > @@ -1296,8 +1296,8 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags) > return res; > } > > -static int memory_failure_dev_pagemap(unsigned long pfn, int flags, > - struct dev_pagemap *pgmap) > +int memory_failure_dev_pagemap(unsigned long pfn, int flags, > + struct dev_pagemap *pgmap) > { > struct page *page = pfn_to_page(pfn); > const bool unmap_success = true; > @@ -1377,6 +1377,13 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags, > unlock: > dax_unlock_page(page, cookie); > out: > + /* > + * In the removal case, given unmap is always successful, and > + * the driver is responsible for the direct map the recovery is > + * always successful > + */ > + if (flags & MF_MEM_REMOVE) > + rc = 0; > action_result(pfn, MF_MSG_DAX, rc ? MF_FAILED : MF_RECOVERED); > return rc; > } > diff --git a/mm/memremap.c b/mm/memremap.c > index 7aa7d6e80ee5..f34da1e14b52 100644 > --- a/mm/memremap.c > +++ b/mm/memremap.c > @@ -165,6 +165,17 @@ static void pageunmap_range(struct dev_pagemap *pgmap, int range_id) > pgmap_array_delete(range); > } > > +void dev_pagemap_failure(struct dev_pagemap *pgmap) > +{ > + unsigned long pfn; > + int i; > + > + for (i = 0; i < pgmap->nr_range; i++) > + for_each_device_pfn(pfn, pgmap, i) > + memory_failure_dev_pagemap(pfn, MF_MEM_REMOVE, pgmap); So my 6TB memory chassis falls off the desk and we have to call memory_failure_dev_pagemap for 1.6 billion PFNs? Honestly if you're going offline the /entire/ device then just tell us sb->memory_failure(dev, 0, -1ULL) and we'll just kill everything all at once. That was where I was trying to push Shiyang's patchset, and I had nearly succeeded when you NAKd the whole thing. In the meantime, I estimate that there are ~45 months worth of deferred XFS patch review that I can make progress on, so that's where I'm going to focus. --D > +} > +EXPORT_SYMBOL_GPL(dev_pagemap_failure); > + > void memunmap_pages(struct dev_pagemap *pgmap) > { > unsigned long pfn; >
