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io_uring: Fix mm_fault with READ/WRITE_FIXED 

Commit fb5ccc9878 ("io_uring: Fix broken links with offloading")
introduced a potential performance regression with unconditionally
taking mm even for READ/WRITE_FIXED operations.

Return the logic handling it back. mm-faulted requests will go through
the generic submission path, so honoring links and drains, but will
fail further on req->has_user check.

Fixes: fb5ccc9878 ("io_uring: Fix broken links with offloading")
Cc: stable@vger.kernel.org # v5.4
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
alistair/sunxi64-5.5-dsi
Pavel Begunkov 2019-10-27 23:15:41 +03:00 committed by Jens Axboe
parent fa45622808
commit 95a1b3ff9a
1 changed files with 17 additions and 24 deletions
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41
fs/io_uring.c
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@ -2726,13 +2726,14 @@ static bool io_get_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
}
static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
bool has_user, bool mm_fault)
struct mm_struct **mm)
{
struct io_submit_state state, *statep = NULL;
struct io_kiocb *link = NULL;
struct io_kiocb *shadow_req = NULL;
bool prev_was_link = false;
int i, submitted = 0;
bool mm_fault = false;
if (nr > IO_PLUG_THRESHOLD) {
io_submit_state_start(&state, ctx, nr);
@ -2745,6 +2746,14 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
if (!io_get_sqring(ctx, &s))
break;
if (io_sqe_needs_user(s.sqe) && !*mm) {
mm_fault = mm_fault || !mmget_not_zero(ctx->sqo_mm);
if (!mm_fault) {
use_mm(ctx->sqo_mm);
*mm = ctx->sqo_mm;
}
}
/*
* If previous wasn't linked and we have a linked command,
* that's the end of the chain. Submit the previous link.
@ -2768,17 +2777,12 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
}
out:
if (unlikely(mm_fault)) {
io_cqring_add_event(ctx, s.sqe->user_data,
-EFAULT);
} else {
s.has_user = has_user;
s.in_async = true;
s.needs_fixed_file = true;
trace_io_uring_submit_sqe(ctx, true, true);
io_submit_sqe(ctx, &s, statep, &link);
submitted++;
}
s.has_user = *mm != NULL;
s.in_async = true;
s.needs_fixed_file = true;
trace_io_uring_submit_sqe(ctx, true, true);
io_submit_sqe(ctx, &s, statep, &link);
submitted++;
}
if (link)
@ -2805,7 +2809,6 @@ static int io_sq_thread(void *data)
timeout = inflight = 0;
while (!kthread_should_park()) {
bool mm_fault = false;
unsigned int to_submit;
if (inflight) {
@ -2890,18 +2893,8 @@ static int io_sq_thread(void *data)
ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP;
}
/* Unless all new commands are FIXED regions, grab mm */
if (!cur_mm) {
mm_fault = !mmget_not_zero(ctx->sqo_mm);
if (!mm_fault) {
use_mm(ctx->sqo_mm);
cur_mm = ctx->sqo_mm;
}
}
to_submit = min(to_submit, ctx->sq_entries);
inflight += io_submit_sqes(ctx, to_submit, cur_mm != NULL,
mm_fault);
inflight += io_submit_sqes(ctx, to_submit, &cur_mm);
/* Commit SQ ring head once we've consumed all SQEs */
io_commit_sqring(ctx);