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gfs2: do_promote glock holder stealing fix

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In do_promote(), when the glock had no strong holders, we were
accidentally calling demote_incompat_holders() with new_gh == NULL, so
no weak holders were considered incompatible.  Instead, the new holder
should have been passed in.

For doing that, the HIF_HOLDER flag needs to be set in new_gh to prevent
may_grant() from complaining.  This means that the new holder will now
be recognized as a current holder, so skip over it explicitly in
demote_incompat_holders() to prevent it from being dequeued.

To further clarify things, we can now rename new_gh to current_gh in
demote_incompat_holders(); after all, the HIF_HOLDER flag is already set,
which means the new holder is already a current holder.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
This commit is contained in:
Bob Peterson 2022-06-11 00:53:32 +02:00 committed by Andreas Gruenbacher
parent 8f0028fc60
commit 0befb8511e
1 changed files with 13 additions and 8 deletions
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21
fs/gfs2/glock.c
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@ -405,10 +405,13 @@ static void do_error(struct gfs2_glock *gl, const int ret)
/**
* demote_incompat_holders - demote incompatible demoteable holders
* @gl: the glock we want to promote
* @new_gh: the new holder to be promoted
* @current_gh: the newly promoted holder
*
* We're passing the newly promoted holder in @current_gh, but actually, any of
* the strong holders would do.
*/
static void demote_incompat_holders(struct gfs2_glock *gl,
struct gfs2_holder *new_gh)
struct gfs2_holder *current_gh)
{
struct gfs2_holder *gh, *tmp;
@ -424,8 +427,10 @@ static void demote_incompat_holders(struct gfs2_glock *gl,
*/
if (!test_bit(HIF_HOLDER, &gh->gh_iflags))
return;
if (gh == current_gh)
continue;
if (test_bit(HIF_MAY_DEMOTE, &gh->gh_iflags) &&
!may_grant(gl, new_gh, gh)) {
!may_grant(gl, current_gh, gh)) {
/*
* We should not recurse into do_promote because
* __gfs2_glock_dq only calls handle_callback,
@ -547,14 +552,14 @@ static int do_promote(struct gfs2_glock *gl)
do_error(gl, 0);
break;
}
if (!incompat_holders_demoted) {
demote_incompat_holders(gl, current_gh);
incompat_holders_demoted = true;
current_gh = gh;
}
set_bit(HIF_HOLDER, &gh->gh_iflags);
trace_gfs2_promote(gh);
gfs2_holder_wake(gh);
if (!incompat_holders_demoted) {
current_gh = gh;
demote_incompat_holders(gl, current_gh);
incompat_holders_demoted = true;
}
}
return 0;
}