From b95a40122a8183873736e0506df8e3a881178099 Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Wed, 22 May 2024 10:26:49 +0200 Subject: [PATCH] iommufd: Use atomic_long_try_cmpxchg() in incr_user_locked_vm() Use atomic_long_try_cmpxchg() instead of atomic_long_cmpxchg (*ptr, old, new) != old in incr_user_locked_vm(). cmpxchg returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, atomic_long_try_cmpxchg() implicitly assigns old *ptr value to "old" when cmpxchg fails. There is no need to re-read the value in the loop. Signed-off-by: Uros Bizjak Cc: Jason Gunthorpe Cc: Kevin Tian Cc: Joerg Roedel Cc: Will Deacon Cc: Robin Murphy Reviewed-by: Jason Gunthorpe Link: https://lore.kernel.org/r/20240522082729.971123-3-ubizjak@gmail.com Signed-off-by: Joerg Roedel --- drivers/iommu/iommufd/pages.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/drivers/iommu/iommufd/pages.c b/drivers/iommu/iommufd/pages.c index 528f356238b3..117f644a0c5b 100644 --- a/drivers/iommu/iommufd/pages.c +++ b/drivers/iommu/iommufd/pages.c @@ -809,13 +809,14 @@ static int incr_user_locked_vm(struct iopt_pages *pages, unsigned long npages) lock_limit = task_rlimit(pages->source_task, RLIMIT_MEMLOCK) >> PAGE_SHIFT; + + cur_pages = atomic_long_read(&pages->source_user->locked_vm); do { - cur_pages = atomic_long_read(&pages->source_user->locked_vm); new_pages = cur_pages + npages; if (new_pages > lock_limit) return -ENOMEM; - } while (atomic_long_cmpxchg(&pages->source_user->locked_vm, cur_pages, - new_pages) != cur_pages); + } while (!atomic_long_try_cmpxchg(&pages->source_user->locked_vm, + &cur_pages, new_pages)); return 0; }