Author: markj Date: Tue Jul 28 19:50:39 2020 New Revision: 363654 URL: https://svnweb.freebsd.org/changeset/base/363654
Log: vm_page_xbusy_claim(): Use atomics to update busy lock state. vm_page_xbusy_claim() could clobber the waiter bit. For its original use, kernel memory pages, this was not a problem since nothing would ever block on the busy lock for such pages. r363607 introduced a new use where this could in principle be a problem. Fix the problem by using atomic_cmpset to update the lock owner. Since this macro is defined only for INVARIANTS kernels the extra overhead doesn't seem prohibitive. Reported by: vangyzen Reviewed by: alc, kib, vangyzen Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D25859 Modified: head/sys/vm/vm_page.h Modified: head/sys/vm/vm_page.h ============================================================================== --- head/sys/vm/vm_page.h Tue Jul 28 19:35:24 2020 (r363653) +++ head/sys/vm/vm_page.h Tue Jul 28 19:50:39 2020 (r363654) @@ -772,8 +772,13 @@ void vm_page_assert_pga_writeable(vm_page_t m, uint16_ #define VM_PAGE_ASSERT_PGA_WRITEABLE(m, bits) \ vm_page_assert_pga_writeable(m, bits) #define vm_page_xbusy_claim(m) do { \ + u_int _busy_lock; \ + \ vm_page_assert_xbusied_unchecked((m)); \ - (m)->busy_lock = VPB_CURTHREAD_EXCLUSIVE; \ + do { \ + _busy_lock = atomic_load_int(&(m)->busy_lock); \ + } while (!atomic_cmpset_int(&(m)->busy_lock, _busy_lock, \ + (_busy_lock & VPB_BIT_FLAGMASK) | VPB_CURTHREAD_EXCLUSIVE)); \ } while (0) #else #define VM_PAGE_OBJECT_BUSY_ASSERT(m) (void)0 _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
