Re: [PATCH v3 3/5] mm: madvise: implement lightweight guard page mechanism
From: Vlastimil Babka <hidden>
Date: 2024-10-25 21:56:54
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linux-alpha, linux-arch, linux-kselftest, linux-mips, linux-mm, lkml
On 10/25/24 19:12, Lorenzo Stoakes wrote:
On Wed, Oct 23, 2024 at 05:24:40PM +0100, Lorenzo Stoakes wrote:quoted
Implement a new lightweight guard page feature, that is regions of userland virtual memory that, when accessed, cause a fatal signal to arise.<snip> Hi Andrew - Could you apply the below fix-patch? I realise we must handle fatal signals and conditional rescheduling in the vector_madvise() special case. Thanks! ----8<---- From 546d7e1831c71599fc733d589e0d75f52e84826d Mon Sep 17 00:00:00 2001 From: Lorenzo Stoakes <redacted> Date: Fri, 25 Oct 2024 18:05:48 +0100 Subject: [PATCH] mm: yield on fatal signal/cond_sched() in vector_madvise() While we have to treat -ERESTARTNOINTR specially here as we are looping through a vector of operations and can't simply restart the entire operation, we mustn't hold up fatal signals or RT kernels.
For plain madvise() syscall returning -ERESTARTNOINTR does the right thing and checks fatal_signal_pending() before returning, right? Uh actually can we be just returning -ERESTARTNOINTR or do we need to use restart_syscall()?
quoted hunk ↗ jump to hunk
--- mm/madvise.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)diff --git a/mm/madvise.c b/mm/madvise.c index 48eba25e25fe..127aa5d86656 100644 --- a/mm/madvise.c +++ b/mm/madvise.c@@ -1713,8 +1713,14 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter, * we have already rescinded locks, it should be no problem to * simply try again. */ - if (ret == -ERESTARTNOINTR) + if (ret == -ERESTARTNOINTR) { + if (fatal_signal_pending(current)) { + ret = -EINTR; + break; + } + cond_resched();
Should be unnecessary as we're calling an operation that takes a rwsem so there are reschedule points already. And with lazy preempt hopefully cond_resched()s will become history, so let's not add more only to delete later.
continue; + } if (ret < 0) break; iov_iter_advance(iter, iter_iov_len(iter)); -- 2.47.0