public inbox for [email protected]
 help / color / mirror / Atom feed
From: Jens Axboe <[email protected]>
To: io-uring <[email protected]>
Subject: [PATCH] io_uring/memmap: move vm_flags_set() outside of ctx->mmap_lock
Date: Thu, 13 Mar 2025 05:44:47 -0600	[thread overview]
Message-ID: <[email protected]> (raw)

syzbot complaints that sometimes the ordering between ctx->mmap_lock
and vma->vm_lock->lock aren't the same, which obviously makes lockdep
unhappy.

We'd normally expect the ctx->mmap_lock to nest inside the vma lock,
but vm_flags_set() -> vma_start_write() from the ->mmap() patch can
happen in the opposite order.

Move the vm_flags_set() to before ctx->mmap_lock is grabbed. This does
potentially leak the VM_DONT_EXPAND set for that vma, and while that
could get cleared, doesn't look like it's necessary to do so. Hence just
keep it simple.

Reported-by: [email protected]
Link: https://lore.kernel.org/io-uring/[email protected]/
Signed-off-by: Jens Axboe <[email protected]>

---

diff --git a/io_uring/memmap.c b/io_uring/memmap.c
index 361134544427..d325b6ab6b99 100644
--- a/io_uring/memmap.c
+++ b/io_uring/memmap.c
@@ -309,7 +309,6 @@ static int io_region_mmap(struct io_ring_ctx *ctx,
 {
 	unsigned long nr_pages = min(mr->nr_pages, max_pages);
 
-	vm_flags_set(vma, VM_DONTEXPAND);
 	return vm_insert_pages(vma, vma->vm_start, mr->pages, &nr_pages);
 }
 
@@ -322,6 +321,8 @@ __cold int io_uring_mmap(struct file *file, struct vm_area_struct *vma)
 	struct io_mapped_region *region;
 	void *ptr;
 
+	vm_flags_set(vma, VM_DONTEXPAND);
+
 	guard(mutex)(&ctx->mmap_lock);
 
 	ptr = io_uring_validate_mmap_request(file, vma->vm_pgoff, sz);

-- 
Jens Axboe


                 reply	other threads:[~2025-03-13 11:44 UTC|newest]

Thread overview: [no followups] expand[flat|nested]  mbox.gz  Atom feed

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    [email protected] \
    [email protected] \
    [email protected] \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox