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gfs2: Simplify DLM_LKF_QUECVT use

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The DLM_LKF_QUECVT flag needs to be set for "upward" lock conversions to
ensure fairness, but setting it for "downward" lock conversions will
lead to a failure.  The flag is currently set based on the GLF_BLOCKING
flag and it's not immediately obvious why this is correct.  Simplify
things by figuring out if a lock conversion is "upward" by looking at
the before and after locking modes instead of relying on the
GLF_BLOCKING flag.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
This commit is contained in:
Andreas Gruenbacher 2024-10-28 22:18:32 +01:00
parent 03ff3781bf
commit b6900ce151
1 changed files with 25 additions and 4 deletions
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29
fs/gfs2/lock_dlm.c
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@ -224,8 +224,21 @@ static int make_mode(struct gfs2_sbd *sdp, const unsigned int lmstate)
return -1;
}
/* Taken from fs/dlm/lock.c. */
static bool middle_conversion(int cur, int req)
{
return (cur == DLM_LOCK_PR && req == DLM_LOCK_CW) ||
(cur == DLM_LOCK_CW && req == DLM_LOCK_PR);
}
static bool down_conversion(int cur, int req)
{
return !middle_conversion(cur, req) && req < cur;
}
static u32 make_flags(struct gfs2_glock *gl, const unsigned int gfs_flags,
const int req)
const int cur, const int req)
{
u32 lkf = 0;
@ -251,7 +264,14 @@ static u32 make_flags(struct gfs2_glock *gl, const unsigned int gfs_flags,
if (!test_bit(GLF_INITIAL, &gl->gl_flags)) {
lkf |= DLM_LKF_CONVERT;
if (test_bit(GLF_BLOCKING, &gl->gl_flags))
/*
* The DLM_LKF_QUECVT flag needs to be set for "first come,
* first served" semantics, but it must only be set for
* "upward" lock conversions or else DLM will reject the
* request as invalid.
*/
if (!down_conversion(cur, req))
lkf |= DLM_LKF_QUECVT;
}
@ -271,13 +291,14 @@ static int gdlm_lock(struct gfs2_glock *gl, unsigned int req_state,
unsigned int flags)
{
struct lm_lockstruct *ls = &gl->gl_name.ln_sbd->sd_lockstruct;
int req;
int cur, req;
u32 lkf;
char strname[GDLM_STRNAME_BYTES] = "";
int error;
cur = make_mode(gl->gl_name.ln_sbd, gl->gl_state);
req = make_mode(gl->gl_name.ln_sbd, req_state);
lkf = make_flags(gl, flags, req);
lkf = make_flags(gl, flags, cur, req);
gfs2_glstats_inc(gl, GFS2_LKS_DCOUNT);
gfs2_sbstats_inc(gl, GFS2_LKS_DCOUNT);
if (test_bit(GLF_INITIAL, &gl->gl_flags)) {