From 021a160abf62c19aff36c920566efb4f690e964a Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 8 Aug 2023 19:26:35 +0200 Subject: fs: use __fput_sync in close(2) close(2) is a special case which guarantees a shallow kernel stack, making delegation to task_work machinery unnecessary. Said delegation is problematic as it involves atomic ops and interrupt masking trips, none of which are cheap on x86-64. Forcing close(2) to do it looks like an oversight in the original work. Moreover presence of CONFIG_RSEQ adds an additional overhead as fput() -> task_work_add(..., TWA_RESUME) -> set_notify_resume() makes the thread returning to userspace land in resume_user_mode_work(), where rseq_handle_notify_resume takes a SMAP round-trip if rseq is enabled for the thread (and it is by default with contemporary glibc). Sample result when benchmarking open1_processes -t 1 from will-it-scale (that's an open + close loop) + tmpfs on /tmp, running on the Sapphire Rapid CPU (ops/s): stock+RSEQ: 1329857 stock-RSEQ: 1421667 (+7%) patched: 1523521 (+14.5% / +7%) (with / without rseq) Patched result is the same regardless of rseq as the codepath is avoided. Signed-off-by: Linus Torvalds Signed-off-by: Christian Brauner --- fs/file_table.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) (limited to 'fs/file_table.c') diff --git a/fs/file_table.c b/fs/file_table.c index fc7d677ff5ad..ee21b3da9d08 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -461,11 +461,8 @@ void fput(struct file *file) */ void __fput_sync(struct file *file) { - if (atomic_long_dec_and_test(&file->f_count)) { - struct task_struct *task = current; - BUG_ON(!(task->flags & PF_KTHREAD)); + if (atomic_long_dec_and_test(&file->f_count)) __fput(file); - } } EXPORT_SYMBOL(fput); -- cgit