Messages in this thread | | | Date | Mon, 10 Aug 2020 19:01:34 -0000 | From | Thomas Gleixner <> | Subject | [GIT pull] locking/urgent for 5.9-rc1 |
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Linus,
please pull the latest locking/urgent branch from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git locking-urgent-2020-08-10
up to: 0cd39f4600ed: locking/seqlock, headers: Untangle the spaghetti monster
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 generaly 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.
Thanks,
tglx
------------------> Ahmed S. Darwish (16): seqlock: Extend seqcount API with associated locks seqlock: Align multi-line macros newline escapes at 72 columns dma-buf: Remove custom seqcount lockdep class key dma-buf: Use sequence counter with associated wound/wait mutex sched: tasks: Use sequence counter with associated spinlock netfilter: conntrack: Use sequence counter with associated spinlock netfilter: nft_set_rbtree: Use sequence counter with associated rwlock xfrm: policy: Use sequence counters with associated lock timekeeping: Use sequence counter with associated raw spinlock vfs: Use sequence counter with associated spinlock raid5: Use sequence counter with associated spinlock iocost: Use sequence counter with associated spinlock NFSv4: Use sequence counter with associated spinlock userfaultfd: Use sequence counter with associated spinlock kvm/eventfd: Use sequence counter with associated spinlock hrtimer: Use sequence counter with associated raw spinlock
Chris Wilson (1): locking/lockdep: Fix overflow in presentation of average lock-time
Ingo Molnar (1): x86/headers: Remove APIC headers from <asm/smp.h>
Peter Zijlstra (7): seqlock: s/__SEQ_LOCKDEP/__SEQ_LOCK/g seqlock: Fold seqcount_LOCKNAME_t definition seqlock: Fold seqcount_LOCKNAME_init() definition seqcount: Compress SEQCNT_LOCKNAME_ZERO() seqcount: More consistent seqprop names locking, arch/ia64: Reduce <asm/smp.h> header dependencies by moving XTP bits into the new <asm/xtp.h> header locking/seqlock, headers: Untangle the spaghetti monster
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