From 0befb8511e6a91716980c40c552acc5eec963cbd Mon Sep 17 00:00:00 2001 From: Bob Peterson Date: Sat, 11 Jun 2022 00:53:32 +0200 Subject: [PATCH] gfs2: do_promote glock holder stealing fix 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 Signed-off-by: Andreas Gruenbacher --- fs/gfs2/glock.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c index 27b519099579..2138460a7369 100644 --- a/fs/gfs2/glock.c +++ b/fs/gfs2/glock.c @@ -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; }