linux/fs/userfaultfd.c, branch v5.9

Merge tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2020-08-11T02:07:44Z

Pull locking updates from Thomas Gleixner: "A set of locking fixes and updates: - Untangle the header spaghetti which causes build failures in various situations caused by the lockdep additions to seqcount to validate that the write side critical sections are non-preemptible. - The seqcount associated lock debug addons which were blocked by the above fallout. seqcount writers contrary to seqlock writers must be externally serialized, which usually happens via locking - except for strict per CPU seqcounts. As the lock is not part of the seqcount, lockdep cannot validate that the lock is held. This new debug mechanism adds the concept of associated locks. sequence count has now lock type variants and corresponding initializers which take a pointer to the associated lock used for writer serialization. If lockdep is enabled the pointer is stored and write_seqcount_begin() has a lockdep assertion to validate that the lock is held. Aside of the type and the initializer no other code changes are required at the seqcount usage sites. The rest of the seqcount API is unchanged and determines the type at compile time with the help of _Generic which is possible now that the minimal GCC version has been moved up. Adding this lockdep coverage unearthed a handful of seqcount bugs which have been addressed already independent of this. While generally useful this comes with a Trojan Horse twist: On RT kernels the write side critical section can become preemtible if the writers are serialized by an associated lock, which leads to the well known reader preempts writer livelock. RT prevents this by storing the associated lock pointer independent of lockdep in the seqcount and changing the reader side to block on the lock when a reader detects that a writer is in the write side critical section. - Conversion of seqcount usage sites to associated types and initializers" * tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (25 commits) locking/seqlock, headers: Untangle the spaghetti monster locking, arch/ia64: Reduce header dependencies by moving XTP bits into the new header x86/headers: Remove APIC headers from seqcount: More consistent seqprop names seqcount: Compress SEQCNT_LOCKNAME_ZERO() seqlock: Fold seqcount_LOCKNAME_init() definition seqlock: Fold seqcount_LOCKNAME_t definition seqlock: s/__SEQ_LOCKDEP/__SEQ_LOCK/g hrtimer: Use sequence counter with associated raw spinlock kvm/eventfd: Use sequence counter with associated spinlock userfaultfd: Use sequence counter with associated spinlock NFSv4: Use sequence counter with associated spinlock iocost: Use sequence counter with associated spinlock raid5: Use sequence counter with associated spinlock vfs: Use sequence counter with associated spinlock timekeeping: Use sequence counter with associated raw spinlock xfrm: policy: Use sequence counters with associated lock netfilter: nft_set_rbtree: Use sequence counter with associated rwlock netfilter: conntrack: Use sequence counter with associated spinlock sched: tasks: Use sequence counter with associated spinlock ...

userfaultfd: simplify fault handling

2020-08-03T18:25:16Z

Instead of waiting in a loop for the userfaultfd condition to become true, just wait once and return VM_FAULT_RETRY. We've already dropped the mmap lock, we know we can't really successfully handle the fault at this point and the caller will have to retry anyway. So there's no point in making the wait any more complicated than it needs to be - just schedule away. And once you don't have that complexity with explicit looping, you can also just lose all the 'userfaultfd_signal_pending()' complexity, because once we've set the correct process sleeping state, and don't loop, the act of scheduling itself will be checking if there are any pending signals before going to sleep. We can also drop the VM_FAULT_MAJOR games, since we'll be treating all retried faults as major soon anyway (series to regularize and share more of fault handling across architectures in a separate series by Peter Xu, and in the meantime we won't worry about the possible minor - I'll be here all week, try the veal - accounting difference). Cc: Andrea Arcangeli Cc: Peter Xu Signed-off-by: Linus Torvalds

userfaultfd: Use sequence counter with associated spinlock

2020-07-29T14:14:28Z

A sequence counter write side critical section must be protected by some form of locking to serialize writers. A plain seqcount_t does not contain the information of which lock must be held when entering a write side critical section. Use the new seqcount_spinlock_t data type, which allows to associate a spinlock with the sequence counter. This enables lockdep to verify that the spinlock used for writer serialization is held when the write side critical section is entered. If lockdep is disabled this lock association is compiled out and has neither storage size nor runtime overhead. Signed-off-by: Ahmed S. Darwish Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200720155530.1173732-23-a.darwish@linutronix.de

mmap locking API: convert mmap_sem comments

2020-06-09T16:39:14Z

Convert comments that reference mmap_sem to reference mmap_lock instead. [akpm@linux-foundation.org: fix up linux-next leftovers] [akpm@linux-foundation.org: s/lockaphore/lock/, per Vlastimil] [akpm@linux-foundation.org: more linux-next fixups, per Michel] Signed-off-by: Michel Lespinasse Signed-off-by: Andrew Morton Reviewed-by: Vlastimil Babka Reviewed-by: Daniel Jordan Cc: Davidlohr Bueso Cc: David Rientjes Cc: Hugh Dickins Cc: Jason Gunthorpe Cc: Jerome Glisse Cc: John Hubbard Cc: Laurent Dufour Cc: Liam Howlett Cc: Matthew Wilcox Cc: Peter Zijlstra Cc: Ying Han Link: http://lkml.kernel.org/r/20200520052908.204642-13-walken@google.com Signed-off-by: Linus Torvalds

mmap locking API: convert mmap_sem API comments

2020-06-09T16:39:14Z

Convert comments that reference old mmap_sem APIs to reference corresponding new mmap locking APIs instead. Signed-off-by: Michel Lespinasse Signed-off-by: Andrew Morton Reviewed-by: Vlastimil Babka Reviewed-by: Davidlohr Bueso Reviewed-by: Daniel Jordan Cc: David Rientjes Cc: Hugh Dickins Cc: Jason Gunthorpe Cc: Jerome Glisse Cc: John Hubbard Cc: Laurent Dufour Cc: Liam Howlett Cc: Matthew Wilcox Cc: Peter Zijlstra Cc: Ying Han Link: http://lkml.kernel.org/r/20200520052908.204642-12-walken@google.com Signed-off-by: Linus Torvalds

mmap locking API: add mmap_assert_locked() and mmap_assert_write_locked()

2020-06-09T16:39:14Z

Add new APIs to assert that mmap_sem is held. Using this instead of rwsem_is_locked and lockdep_assert_held[_write] makes the assertions more tolerant of future changes to the lock type. Signed-off-by: Michel Lespinasse Signed-off-by: Andrew Morton Reviewed-by: Vlastimil Babka Reviewed-by: Daniel Jordan Cc: Davidlohr Bueso Cc: David Rientjes Cc: Hugh Dickins Cc: Jason Gunthorpe Cc: Jerome Glisse Cc: John Hubbard Cc: Laurent Dufour Cc: Liam Howlett Cc: Matthew Wilcox Cc: Peter Zijlstra Cc: Ying Han Link: http://lkml.kernel.org/r/20200520052908.204642-10-walken@google.com Signed-off-by: Linus Torvalds

mmap locking API: use coccinelle to convert mmap_sem rwsem call sites

2020-06-09T16:39:14Z

This change converts the existing mmap_sem rwsem calls to use the new mmap locking API instead. The change is generated using coccinelle with the following rule: // spatch --sp-file mmap_lock_api.cocci --in-place --include-headers --dir . @@ expression mm; @@ ( -init_rwsem +mmap_init_lock | -down_write +mmap_write_lock | -down_write_killable +mmap_write_lock_killable | -down_write_trylock +mmap_write_trylock | -up_write +mmap_write_unlock | -downgrade_write +mmap_write_downgrade | -down_read +mmap_read_lock | -down_read_killable +mmap_read_lock_killable | -down_read_trylock +mmap_read_trylock | -up_read +mmap_read_unlock ) -(&mm->mmap_sem) +(mm) Signed-off-by: Michel Lespinasse Signed-off-by: Andrew Morton Reviewed-by: Daniel Jordan Reviewed-by: Laurent Dufour Reviewed-by: Vlastimil Babka Cc: Davidlohr Bueso Cc: David Rientjes Cc: Hugh Dickins Cc: Jason Gunthorpe Cc: Jerome Glisse Cc: John Hubbard Cc: Liam Howlett Cc: Matthew Wilcox Cc: Peter Zijlstra Cc: Ying Han Link: http://lkml.kernel.org/r/20200520052908.204642-5-walken@google.com Signed-off-by: Linus Torvalds

userfaultfd: wp: declare _UFFDIO_WRITEPROTECT conditionally

2020-04-07T17:43:40Z

Only declare _UFFDIO_WRITEPROTECT if the user specified UFFDIO_REGISTER_MODE_WP and if all the checks passed. Then when the user registers regions with shmem/hugetlbfs we won't expose the new ioctl to them. Even with complete anonymous memory range, we'll only expose the new WP ioctl bit if the register mode has MODE_WP. Signed-off-by: Peter Xu Signed-off-by: Andrew Morton Reviewed-by: Mike Rapoport Cc: Andrea Arcangeli Cc: Bobby Powers Cc: Brian Geffon Cc: David Hildenbrand Cc: Denis Plotnikov Cc: "Dr . David Alan Gilbert" Cc: Hugh Dickins Cc: Jerome Glisse Cc: Johannes Weiner Cc: "Kirill A . Shutemov" Cc: Martin Cracauer Cc: Marty McFadden Cc: Maya Gokhale Cc: Mel Gorman Cc: Mike Kravetz Cc: Pavel Emelyanov Cc: Rik van Riel Cc: Shaohua Li Link: http://lkml.kernel.org/r/20200220163112.11409-18-peterx@redhat.com Signed-off-by: Linus Torvalds

userfaultfd: wp: don't wake up when doing write protect

2020-04-07T17:43:39Z

It does not make sense to try to wake up any waiting thread when we're write-protecting a memory region. Only wake up when resolving a write protected page fault. Signed-off-by: Peter Xu Signed-off-by: Andrew Morton Reviewed-by: Mike Rapoport Cc: Andrea Arcangeli Cc: Bobby Powers Cc: Brian Geffon Cc: David Hildenbrand Cc: Denis Plotnikov Cc: "Dr . David Alan Gilbert" Cc: Hugh Dickins Cc: Jerome Glisse Cc: Johannes Weiner Cc: "Kirill A . Shutemov" Cc: Martin Cracauer Cc: Marty McFadden Cc: Maya Gokhale Cc: Mel Gorman Cc: Mike Kravetz Cc: Pavel Emelyanov Cc: Rik van Riel Cc: Shaohua Li Link: http://lkml.kernel.org/r/20200220163112.11409-16-peterx@redhat.com Signed-off-by: Linus Torvalds

userfaultfd: wp: add the writeprotect API to userfaultfd ioctl

2020-04-07T17:43:39Z

Introduce the new uffd-wp APIs for userspace. Firstly, we'll allow to do UFFDIO_REGISTER with write protection tracking using the new UFFDIO_REGISTER_MODE_WP flag. Note that this flag can co-exist with the existing UFFDIO_REGISTER_MODE_MISSING, in which case the userspace program can not only resolve missing page faults, and at the same time tracking page data changes along the way. Secondly, we introduced the new UFFDIO_WRITEPROTECT API to do page level write protection tracking. Note that we will need to register the memory region with UFFDIO_REGISTER_MODE_WP before that. [peterx@redhat.com: write up the commit message] [peterx@redhat.com: remove useless block, write commit message, check against VM_MAYWRITE rather than VM_WRITE when register] Signed-off-by: Andrea Arcangeli Signed-off-by: Peter Xu Signed-off-by: Andrew Morton Reviewed-by: Jerome Glisse Cc: Bobby Powers Cc: Brian Geffon Cc: David Hildenbrand Cc: Denis Plotnikov Cc: "Dr . David Alan Gilbert" Cc: Hugh Dickins Cc: Johannes Weiner Cc: "Kirill A . Shutemov" Cc: Martin Cracauer Cc: Marty McFadden Cc: Maya Gokhale Cc: Mel Gorman Cc: Mike Kravetz Cc: Mike Rapoport Cc: Pavel Emelyanov Cc: Rik van Riel Cc: Shaohua Li Link: http://lkml.kernel.org/r/20200220163112.11409-14-peterx@redhat.com Signed-off-by: Linus Torvalds