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author | Herbert Xu <herbert@gondor.apana.org.au> | 2017-01-12 16:10:00 +0800 |
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committer | Herbert Xu <herbert@gondor.apana.org.au> | 2017-01-12 16:10:00 +0800 |
commit | 4cf0662888026d5c1b62ed3fa8dc048a2ff2e124 (patch) | |
tree | a5c92c5024c599a00bfd8d402d2b7b0a619b0259 /mm/filemap.c | |
parent | c821f6ab2e47946f35ee2f30781c5185e5d07f65 (diff) | |
parent | a121103c922847ba5010819a3f250f1f7fc84ab8 (diff) | |
download | op-kernel-dev-4cf0662888026d5c1b62ed3fa8dc048a2ff2e124.zip op-kernel-dev-4cf0662888026d5c1b62ed3fa8dc048a2ff2e124.tar.gz |
Merge git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux
Merging 4.10-rc3 so that the cryptodev tree builds on ARM64.
Diffstat (limited to 'mm/filemap.c')
-rw-r--r-- | mm/filemap.c | 36 |
1 files changed, 31 insertions, 5 deletions
diff --git a/mm/filemap.c b/mm/filemap.c index 82f26cd..d0e4d10 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -912,6 +912,29 @@ void add_page_wait_queue(struct page *page, wait_queue_t *waiter) } EXPORT_SYMBOL_GPL(add_page_wait_queue); +#ifndef clear_bit_unlock_is_negative_byte + +/* + * PG_waiters is the high bit in the same byte as PG_lock. + * + * On x86 (and on many other architectures), we can clear PG_lock and + * test the sign bit at the same time. But if the architecture does + * not support that special operation, we just do this all by hand + * instead. + * + * The read of PG_waiters has to be after (or concurrently with) PG_locked + * being cleared, but a memory barrier should be unneccssary since it is + * in the same byte as PG_locked. + */ +static inline bool clear_bit_unlock_is_negative_byte(long nr, volatile void *mem) +{ + clear_bit_unlock(nr, mem); + /* smp_mb__after_atomic(); */ + return test_bit(PG_waiters, mem); +} + +#endif + /** * unlock_page - unlock a locked page * @page: the page @@ -921,16 +944,19 @@ EXPORT_SYMBOL_GPL(add_page_wait_queue); * mechanism between PageLocked pages and PageWriteback pages is shared. * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep. * - * The mb is necessary to enforce ordering between the clear_bit and the read - * of the waitqueue (to avoid SMP races with a parallel wait_on_page_locked()). + * Note that this depends on PG_waiters being the sign bit in the byte + * that contains PG_locked - thus the BUILD_BUG_ON(). That allows us to + * clear the PG_locked bit and test PG_waiters at the same time fairly + * portably (architectures that do LL/SC can test any bit, while x86 can + * test the sign bit). */ void unlock_page(struct page *page) { + BUILD_BUG_ON(PG_waiters != 7); page = compound_head(page); VM_BUG_ON_PAGE(!PageLocked(page), page); - clear_bit_unlock(PG_locked, &page->flags); - smp_mb__after_atomic(); - wake_up_page(page, PG_locked); + if (clear_bit_unlock_is_negative_byte(PG_locked, &page->flags)) + wake_up_page_bit(page, PG_locked); } EXPORT_SYMBOL(unlock_page); |