From e3da6be3d70449a1f14c99f13cc1eb453a2be4ea Mon Sep 17 00:00:00 2001
From: Andreas Gruenbacher <agruenba@redhat.com>
Date: Wed, 30 Aug 2023 22:09:36 +0200
Subject: [PATCH] gfs2: Fix withdraw race
Function gfs2_withdraw() tries to synchronize concurrent callers by
atomically setting the SDF_WITHDRAWN flag in the first caller, setting
the SDF_WITHDRAW_IN_PROG flag to indicate that a withdraw is in
progress, performing the actual withdraw, and clearing the
SDF_WITHDRAW_IN_PROG flag when done. All other callers wait for the
SDF_WITHDRAW_IN_PROG flag to be cleared before returning.
This leaves a small window in which callers can find the SDF_WITHDRAWN
flag set before the SDF_WITHDRAW_IN_PROG flag has been set, causing them
to return prematurely, before the withdraw has been completed.
Fix that by setting the SDF_WITHDRAWN and SDF_WITHDRAW_IN_PROG flags
atomically.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
fs/gfs2/util.c | 24 ++++++++++++------------
1 file changed, 12 insertions(+), 12 deletions(-)
diff --git a/fs/gfs2/util.c b/fs/gfs2/util.c
index 65a3c7b1a51e9..da29fafb62728 100644
--- a/fs/gfs2/util.c
+++ b/fs/gfs2/util.c
@@ -323,19 +323,19 @@ int gfs2_withdraw(struct gfs2_sbd *sdp)
struct lm_lockstruct *ls = &sdp->sd_lockstruct;
const struct lm_lockops *lm = ls->ls_ops;
- if (sdp->sd_args.ar_errors == GFS2_ERRORS_WITHDRAW &&
- test_and_set_bit(SDF_WITHDRAWN, &sdp->sd_flags)) {
- if (!test_bit(SDF_WITHDRAW_IN_PROG, &sdp->sd_flags))
- return -1;
-
- wait_on_bit(&sdp->sd_flags, SDF_WITHDRAW_IN_PROG,
- TASK_UNINTERRUPTIBLE);
- return -1;
- }
-
- set_bit(SDF_WITHDRAW_IN_PROG, &sdp->sd_flags);
-
if (sdp->sd_args.ar_errors == GFS2_ERRORS_WITHDRAW) {
+ unsigned long old = READ_ONCE(sdp->sd_flags), new;
+
+ do {
+ if (old & BIT(SDF_WITHDRAWN)) {
+ wait_on_bit(&sdp->sd_flags,
+ SDF_WITHDRAW_IN_PROG,
+ TASK_UNINTERRUPTIBLE);
+ return -1;
+ }
+ new = old | BIT(SDF_WITHDRAWN) | BIT(SDF_WITHDRAW_IN_PROG);
+ } while (unlikely(!try_cmpxchg(&sdp->sd_flags, &old, new)));
+
fs_err(sdp, "about to withdraw this file system\n");
BUG_ON(sdp->sd_args.ar_debug);
--
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