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gfs2: Fix withdraw race

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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>
This commit is contained in:
Andreas Gruenbacher 2023-08-30 22:09:36 +02:00
parent fe0690f0a6
commit e3da6be3d7
1 changed files with 12 additions and 12 deletions
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24
fs/gfs2/util.c
View file

@ -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);