Commit 6b7898eb authored Aug 25, 2020 by Jens Axboe

io_uring: fix imbalanced sqo_mm accounting



We do the initial accounting of locked_vm and pinned_vm before we have
setup ctx->sqo_mm, which means we can end up having not accounted the
memory at setup time, but still decrement it when we exit. This causes
an imbalance in the accounting.

Setup ctx->sqo_mm earlier in io_uring_create(), before we do the first
accounting of mm->{locked,pinned}_vm. This also unifies the state
grabbing for the ctx, and eliminates a failure case in
io_sq_offload_start().

Fixes: f74441e6 ("io_uring: account locked memory before potential error case")
Reported-by: Robert M. Muncrief <rmuncrief@humanavance.com>
Reported-by: Niklas Schnelle <schnelle@linux.ibm.com>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
Tested-by: Robert M. Muncrief <rmuncrief@humanavance.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 84216315

fs/io_uring.c

+3 −7

Original line number	Diff line number	Diff line
		@@ -7447,9 +7447,6 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
		{
		int ret;

		mmgrab(current->mm);
		ctx->sqo_mm = current->mm;

		if (ctx->flags & IORING_SETUP_SQPOLL) {
		ret = -EPERM;
		if (!capable(CAP_SYS_ADMIN))
		@@ -7494,10 +7491,6 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
		return 0;
		err:
		io_finish_async(ctx);
		if (ctx->sqo_mm) {
		mmdrop(ctx->sqo_mm);
		ctx->sqo_mm = NULL;
		}
		return ret;
		}

		@@ -8547,6 +8540,9 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p,
		ctx->user = user;
		ctx->creds = get_current_cred();

		mmgrab(current->mm);
		ctx->sqo_mm = current->mm;

		/*
		* Account memory _before_ installing the file descriptor. Once
		* the descriptor is installed, it can get closed at any time. Also

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