[PATCH 2/2] io_uring: hold mmap_sem for mm->locked_vm manipulation

[Jens Axboe <axboe@kernel.dk>]

The kernel doesn't seem to have clear rules around this, but various
spots are using the mmap_sem to serialize access to modifying the
locked_vm count. Play it safe and lock the mm for write when accounting
or unaccounting locked memory.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6a4560c9ed9a..2d07d35e7262 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8157,10 +8157,13 @@ static void io_unaccount_mem(struct io_ring_ctx *ctx, unsigned long nr_pages,
 		__io_unaccount_mem(ctx->user, nr_pages);
 
 	if (ctx->mm_account) {
-		if (acct == ACCT_LOCKED)
+		if (acct == ACCT_LOCKED) {
+			mmap_write_lock(ctx->mm_account);
 			ctx->mm_account->locked_vm -= nr_pages;
-		else if (acct == ACCT_PINNED)
+			mmap_write_unlock(ctx->mm_account);
+		}else if (acct == ACCT_PINNED) {
 			atomic64_sub(nr_pages, &ctx->mm_account->pinned_vm);
+		}
 	}
 }
 
@@ -8176,10 +8179,13 @@ static int io_account_mem(struct io_ring_ctx *ctx, unsigned long nr_pages,
 	}
 
 	if (ctx->mm_account) {
-		if (acct == ACCT_LOCKED)
+		if (acct == ACCT_LOCKED) {
+			mmap_write_lock(ctx->mm_account);
 			ctx->mm_account->locked_vm += nr_pages;
-		else if (acct == ACCT_PINNED)
+			mmap_write_unlock(ctx->mm_account);
+		} else if (acct == ACCT_PINNED) {
 			atomic64_add(nr_pages, &ctx->mm_account->pinned_vm);
+		}
 	}
 
 	return 0;
-- 
2.29.2