linux/mm/debug.c, branch v5.7

mm: dump_page(): additional diagnostics for huge pinned pages

2020-04-02T16:35:27Z

As part of pin_user_pages() and related API calls, pages are "dma-pinned". For the case of compound pages of order > 1, the per-page accounting of dma pins is accomplished via the 3rd struct page in the compound page. In order to support debugging of any pin_user_pages()- related problems, enhance dump_page() so as to report the pin count in that case. Documentation/core-api/pin_user_pages.rst is also updated accordingly. Signed-off-by: John Hubbard Signed-off-by: Andrew Morton Acked-by: Kirill A. Shutemov Cc: Jan Kara Cc: Matthew Wilcox Cc: Ira Weiny Cc: Jérôme Glisse Cc: Al Viro Cc: Christoph Hellwig Cc: Dan Williams Cc: Dave Chinner Cc: Jason Gunthorpe Cc: Jonathan Corbet Cc: Michal Hocko Cc: Mike Kravetz Cc: Shuah Khan Cc: Vlastimil Babka Link: http://lkml.kernel.org/r/20200211001536.1027652-13-jhubbard@nvidia.com Signed-off-by: Linus Torvalds

mm: improve dump_page() for compound pages

2020-04-02T16:35:27Z

There was no protection against a corrupted struct page having an implausible compound_head(). Sanity check that a compound page has a head within reach of the maximum allocatable page (this will need to be adjusted if one of the plans to allocate 1GB pages comes to fruition). In addition, - Print the mapping pointer using %p insted of %px. The actual value of the pointer can be read out of the raw page dump and using %p gives a chance to correlate it with an earlier printk of the mapping pointer - Print the mapping pointer from the head page, not the tail page (the tail ->mapping pointer may be in use for other purposes, eg part of a list_head) - Print the order of the page for compound pages - Dump the raw head page as well as the raw page - Print the refcount from the head page, not the tail page Suggested-by: Kirill A. Shutemov Co-developed-by: John Hubbard Signed-off-by: Matthew Wilcox (Oracle) Signed-off-by: John Hubbard Signed-off-by: Andrew Morton Cc: Ira Weiny Cc: Jan Kara Cc: Jérôme Glisse Cc: Al Viro Cc: Christoph Hellwig Cc: Dan Williams Cc: Dave Chinner Cc: Jason Gunthorpe Cc: Jonathan Corbet Cc: Michal Hocko Cc: Mike Kravetz Cc: Shuah Khan Cc: Vlastimil Babka Link: http://lkml.kernel.org/r/20200211001536.1027652-12-jhubbard@nvidia.com Signed-off-by: Linus Torvalds

mm/hotplug: silence a lockdep splat with printk()

2020-01-31T18:30:39Z

It is not that hard to trigger lockdep splats by calling printk from under zone->lock. Most of them are false positives caused by lock chains introduced early in the boot process and they do not cause any real problems (although most of the early boot lock dependencies could happen after boot as well). There are some console drivers which do allocate from the printk context as well and those should be fixed. In any case, false positives are not that trivial to workaround and it is far from optimal to lose lockdep functionality for something that is a non-issue. So change has_unmovable_pages() so that it no longer calls dump_page() itself - instead it returns a "struct page *" of the unmovable page back to the caller so that in the case of a has_unmovable_pages() failure, the caller can call dump_page() after releasing zone->lock. Also, make dump_page() is able to report a CMA page as well, so the reason string from has_unmovable_pages() can be removed. Even though has_unmovable_pages doesn't hold any reference to the returned page this should be reasonably safe for the purpose of reporting the page (dump_page) because it cannot be hotremoved in the context of memory unplug. The state of the page might change but that is the case even with the existing code as zone->lock only plays role for free pages. While at it, remove a similar but unnecessary debug-only printk() as well. A sample of one of those lockdep splats is, WARNING: possible circular locking dependency detected ------------------------------------------------------ test.sh/8653 is trying to acquire lock: ffffffff865a4460 (console_owner){-.-.}, at: console_unlock+0x207/0x750 but task is already holding lock: ffff88883fff3c58 (&(&zone->lock)->rlock){-.-.}, at: __offline_isolated_pages+0x179/0x3e0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (&(&zone->lock)->rlock){-.-.}: __lock_acquire+0x5b3/0xb40 lock_acquire+0x126/0x280 _raw_spin_lock+0x2f/0x40 rmqueue_bulk.constprop.21+0xb6/0x1160 get_page_from_freelist+0x898/0x22c0 __alloc_pages_nodemask+0x2f3/0x1cd0 alloc_pages_current+0x9c/0x110 allocate_slab+0x4c6/0x19c0 new_slab+0x46/0x70 ___slab_alloc+0x58b/0x960 __slab_alloc+0x43/0x70 __kmalloc+0x3ad/0x4b0 __tty_buffer_request_room+0x100/0x250 tty_insert_flip_string_fixed_flag+0x67/0x110 pty_write+0xa2/0xf0 n_tty_write+0x36b/0x7b0 tty_write+0x284/0x4c0 __vfs_write+0x50/0xa0 vfs_write+0x105/0x290 redirected_tty_write+0x6a/0xc0 do_iter_write+0x248/0x2a0 vfs_writev+0x106/0x1e0 do_writev+0xd4/0x180 __x64_sys_writev+0x45/0x50 do_syscall_64+0xcc/0x76c entry_SYSCALL_64_after_hwframe+0x49/0xbe -> #2 (&(&port->lock)->rlock){-.-.}: __lock_acquire+0x5b3/0xb40 lock_acquire+0x126/0x280 _raw_spin_lock_irqsave+0x3a/0x50 tty_port_tty_get+0x20/0x60 tty_port_default_wakeup+0xf/0x30 tty_port_tty_wakeup+0x39/0x40 uart_write_wakeup+0x2a/0x40 serial8250_tx_chars+0x22e/0x440 serial8250_handle_irq.part.8+0x14a/0x170 serial8250_default_handle_irq+0x5c/0x90 serial8250_interrupt+0xa6/0x130 __handle_irq_event_percpu+0x78/0x4f0 handle_irq_event_percpu+0x70/0x100 handle_irq_event+0x5a/0x8b handle_edge_irq+0x117/0x370 do_IRQ+0x9e/0x1e0 ret_from_intr+0x0/0x2a cpuidle_enter_state+0x156/0x8e0 cpuidle_enter+0x41/0x70 call_cpuidle+0x5e/0x90 do_idle+0x333/0x370 cpu_startup_entry+0x1d/0x1f start_secondary+0x290/0x330 secondary_startup_64+0xb6/0xc0 -> #1 (&port_lock_key){-.-.}: __lock_acquire+0x5b3/0xb40 lock_acquire+0x126/0x280 _raw_spin_lock_irqsave+0x3a/0x50 serial8250_console_write+0x3e4/0x450 univ8250_console_write+0x4b/0x60 console_unlock+0x501/0x750 vprintk_emit+0x10d/0x340 vprintk_default+0x1f/0x30 vprintk_func+0x44/0xd4 printk+0x9f/0xc5 -> #0 (console_owner){-.-.}: check_prev_add+0x107/0xea0 validate_chain+0x8fc/0x1200 __lock_acquire+0x5b3/0xb40 lock_acquire+0x126/0x280 console_unlock+0x269/0x750 vprintk_emit+0x10d/0x340 vprintk_default+0x1f/0x30 vprintk_func+0x44/0xd4 printk+0x9f/0xc5 __offline_isolated_pages.cold.52+0x2f/0x30a offline_isolated_pages_cb+0x17/0x30 walk_system_ram_range+0xda/0x160 __offline_pages+0x79c/0xa10 offline_pages+0x11/0x20 memory_subsys_offline+0x7e/0xc0 device_offline+0xd5/0x110 state_store+0xc6/0xe0 dev_attr_store+0x3f/0x60 sysfs_kf_write+0x89/0xb0 kernfs_fop_write+0x188/0x240 __vfs_write+0x50/0xa0 vfs_write+0x105/0x290 ksys_write+0xc6/0x160 __x64_sys_write+0x43/0x50 do_syscall_64+0xcc/0x76c entry_SYSCALL_64_after_hwframe+0x49/0xbe other info that might help us debug this: Chain exists of: console_owner --> &(&port->lock)->rlock --> &(&zone->lock)->rlock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&(&zone->lock)->rlock); lock(&(&port->lock)->rlock); lock(&(&zone->lock)->rlock); lock(console_owner); *** DEADLOCK *** 9 locks held by test.sh/8653: #0: ffff88839ba7d408 (sb_writers#4){.+.+}, at: vfs_write+0x25f/0x290 #1: ffff888277618880 (&of->mutex){+.+.}, at: kernfs_fop_write+0x128/0x240 #2: ffff8898131fc218 (kn->count#115){.+.+}, at: kernfs_fop_write+0x138/0x240 #3: ffffffff86962a80 (device_hotplug_lock){+.+.}, at: lock_device_hotplug_sysfs+0x16/0x50 #4: ffff8884374f4990 (&dev->mutex){....}, at: device_offline+0x70/0x110 #5: ffffffff86515250 (cpu_hotplug_lock.rw_sem){++++}, at: __offline_pages+0xbf/0xa10 #6: ffffffff867405f0 (mem_hotplug_lock.rw_sem){++++}, at: percpu_down_write+0x87/0x2f0 #7: ffff88883fff3c58 (&(&zone->lock)->rlock){-.-.}, at: __offline_isolated_pages+0x179/0x3e0 #8: ffffffff865a4920 (console_lock){+.+.}, at: vprintk_emit+0x100/0x340 stack backtrace: Hardware name: HPE ProLiant DL560 Gen10/ProLiant DL560 Gen10, BIOS U34 05/21/2019 Call Trace: dump_stack+0x86/0xca print_circular_bug.cold.31+0x243/0x26e check_noncircular+0x29e/0x2e0 check_prev_add+0x107/0xea0 validate_chain+0x8fc/0x1200 __lock_acquire+0x5b3/0xb40 lock_acquire+0x126/0x280 console_unlock+0x269/0x750 vprintk_emit+0x10d/0x340 vprintk_default+0x1f/0x30 vprintk_func+0x44/0xd4 printk+0x9f/0xc5 __offline_isolated_pages.cold.52+0x2f/0x30a offline_isolated_pages_cb+0x17/0x30 walk_system_ram_range+0xda/0x160 __offline_pages+0x79c/0xa10 offline_pages+0x11/0x20 memory_subsys_offline+0x7e/0xc0 device_offline+0xd5/0x110 state_store+0xc6/0xe0 dev_attr_store+0x3f/0x60 sysfs_kf_write+0x89/0xb0 kernfs_fop_write+0x188/0x240 __vfs_write+0x50/0xa0 vfs_write+0x105/0x290 ksys_write+0xc6/0x160 __x64_sys_write+0x43/0x50 do_syscall_64+0xcc/0x76c entry_SYSCALL_64_after_hwframe+0x49/0xbe Link: http://lkml.kernel.org/r/20200117181200.20299-1-cai@lca.pw Signed-off-by: Qian Cai Reviewed-by: David Hildenbrand Cc: Michal Hocko Cc: Sergey Senozhatsky Cc: Petr Mladek Cc: Steven Rostedt (VMware) Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/debug.c: always print flags in dump_page()

2020-01-31T18:30:36Z

Commit 76a1850e4572 ("mm/debug.c: __dump_page() prints an extra line") inadvertently removed printing of page flags for pages that are neither anon nor ksm nor have a mapping. Fix that. Using pr_cont() again would be a solution, but the commit explicitly removed its use. Avoiding the danger of mixing up split lines from multiple CPUs might be beneficial for near-panic dumps like this, so fix this without reintroducing pr_cont(). Link: http://lkml.kernel.org/r/9f884d5c-ca60-dc7b-219c-c081c755fab6@suse.cz Fixes: 76a1850e4572 ("mm/debug.c: __dump_page() prints an extra line") Signed-off-by: Vlastimil Babka Reported-by: Anshuman Khandual Reported-by: Michal Hocko Acked-by: Michal Hocko Cc: David Hildenbrand Cc: Qian Cai Cc: Oscar Salvador Cc: Mel Gorman Cc: Mike Rapoport Cc: Dan Williams Cc: Pavel Tatashin Cc: Ralph Campbell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/mmu_notifier: Rename struct mmu_notifier_mm to mmu_notifier_subscriptions

2020-01-14T15:54:47Z

The name mmu_notifier_mm implies that the thing is a mm_struct pointer, and is difficult to abbreviate. The struct is actually holding the interval tree and hlist containing the notifiers subscribed to a mm. Use 'subscriptions' as the variable name for this struct instead of the really terrible and misleading 'mmn_mm'. Signed-off-by: Jason Gunthorpe

mm/debug.c: PageAnon() is true for PageKsm() pages

2019-11-16T02:34:00Z

PageAnon() and PageKsm() use the low two bits of the page->mapping pointer to indicate the page type. PageAnon() only checks the LSB while PageKsm() checks the least significant 2 bits are equal to 3. Therefore, PageAnon() is true for KSM pages. __dump_page() incorrectly will never print "ksm" because it checks PageAnon() first. Fix this by checking PageKsm() first. Link: http://lkml.kernel.org/r/20191113000651.20677-1-rcampbell@nvidia.com Fixes: 1c6fb1d89e73 ("mm: print more information about mapping in __dump_page") Signed-off-by: Ralph Campbell Acked-by: Michal Hocko Cc: Jerome Glisse Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/debug.c: __dump_page() prints an extra line

2019-11-16T02:34:00Z

When dumping struct page information, __dump_page() prints the page type with a trailing blank followed by the page flags on a separate line: anon flags: 0x100000000090034(uptodate|lru|active|head|swapbacked) It looks like the intent was to use pr_cont() for printing "flags:" but pr_cont() usage is discouraged so fix this by extending the format to include the flags into a single line: anon flags: 0x100000000090034(uptodate|lru|active|head|swapbacked) If the page is file backed, the name might be long so use two lines: shmem_aops name:"dev/zero" flags: 0x10000000008000c(uptodate|dirty|swapbacked) Eliminate pr_conf() usage as well for appending compound_mapcount. Link: http://lkml.kernel.org/r/20191112012608.16926-1-rcampbell@nvidia.com Signed-off-by: Ralph Campbell Reviewed-by: Andrew Morton Cc: Jerome Glisse Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: update references to page _refcount

2019-05-15T02:52:47Z

Commit 0139aa7b7fa ("mm: rename _count, field of the struct page, to _refcount") left out a couple of references to the old field name. Fix that. Link: http://lkml.kernel.org/r/cedf87b02eb8a6b3eac57e8e91da53fb15c3c44c.1556537475.git.baruch@tkos.co.il Fixes: 0139aa7b7fa ("mm: rename _count, field of the struct page, to _refcount") Signed-off-by: Baruch Siach Reviewed-by: Andrew Morton Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/debug.c: fix __dump_page when mapping->host is not set

2019-03-29T17:01:37Z

While debugging something, I added a dump_page() into do_swap_page(), and I got the splat from below. The issue happens when dereferencing mapping->host in __dump_page(): ... else if (mapping) { pr_warn("%ps ", mapping->a_ops); if (mapping->host->i_dentry.first) { struct dentry *dentry; dentry = container_of(mapping->host->i_dentry.first, struct dentry, d_u.d_alias); pr_warn("name:\"%pd\" ", dentry); } } ... Swap address space does not contain an inode information, and so mapping->host equals NULL. Although the dump_page() call was added artificially into do_swap_page(), I am not sure if we can hit this from any other path, so it looks worth fixing it. We can easily do that by checking mapping->host first. Link: http://lkml.kernel.org/r/20190318072931.29094-1-osalvador@suse.de Fixes: 1c6fb1d89e73c ("mm: print more information about mapping in __dump_page") Signed-off-by: Oscar Salvador Acked-by: Michal Hocko Acked-by: Hugh Dickins Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/debug.c: add a cast to u64 for atomic64_read()

2019-03-29T17:01:37Z

atomic64_read() on ppc64le returns "long int", so fix the same way as commit d549f545e690 ("drm/virtio: use %llu format string form atomic64_t") by adding a cast to u64, which makes it work on all arches. In file included from ./include/linux/printk.h:7, from ./include/linux/kernel.h:15, from mm/debug.c:9: mm/debug.c: In function 'dump_mm': ./include/linux/kern_levels.h:5:18: warning: format '%llx' expects argument of type 'long long unsigned int', but argument 19 has type 'long int' [-Wformat=] #define KERN_SOH "A" /* ASCII Start Of Header */ ^~~~~~ ./include/linux/kern_levels.h:8:20: note: in expansion of macro 'KERN_SOH' #define KERN_EMERG KERN_SOH "0" /* system is unusable */ ^~~~~~~~ ./include/linux/printk.h:297:9: note: in expansion of macro 'KERN_EMERG' printk(KERN_EMERG pr_fmt(fmt), ##__VA_ARGS__) ^~~~~~~~~~ mm/debug.c:133:2: note: in expansion of macro 'pr_emerg' pr_emerg("mm %px mmap %px seqnum %llu task_size %lu" ^~~~~~~~ mm/debug.c:140:17: note: format string is defined here "pinned_vm %llx data_vm %lx exec_vm %lx stack_vm %lx" ~~~^ %lx Link: http://lkml.kernel.org/r/20190310183051.87303-1-cai@lca.pw Fixes: 70f8a3ca68d3 ("mm: make mm->pinned_vm an atomic64 counter") Signed-off-by: Qian Cai Acked-by: Davidlohr Bueso Cc: Jason Gunthorpe Cc: Arnd Bergmann Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds