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GFS2: Request demote when a "try" flock fails 

This patch changes the flock code so that it uses the TRY_1CB flag
instead of the TRY flag on the first attempt. That forces any holding
nodes to issue a dlm callback, which requests a demote of the glock.
Then, if the "try" failed, it sleeps a small amount of time for the
demote to occur. Then it tries again, for an increasing amount of time.
Subsequent attempts to gain the "try" lock don't use "_1CB" so that
only one callback is issued.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
This commit is contained in:
Bob Peterson 2014-08-20 12:44:45 -04:00 committed by Steven Whitehouse
parent b650738cd0
commit 2ddfbdd684
1 changed files with 12 additions and 3 deletions
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15
fs/gfs2/file.c
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@ -26,6 +26,7 @@
#include <linux/dlm.h>
#include <linux/dlm_plock.h>
#include <linux/aio.h>
#include <linux/delay.h>
#include "gfs2.h"
#include "incore.h"
@ -979,9 +980,10 @@ static int do_flock(struct file *file, int cmd, struct file_lock *fl)
unsigned int state;
int flags;
int error = 0;
int sleeptime;
state = (fl->fl_type == F_WRLCK) ? LM_ST_EXCLUSIVE : LM_ST_SHARED;
flags = (IS_SETLKW(cmd) ? 0 : LM_FLAG_TRY) | GL_EXACT;
flags = (IS_SETLKW(cmd) ? 0 : LM_FLAG_TRY_1CB) | GL_EXACT;
mutex_lock(&fp->f_fl_mutex);
@ -1001,7 +1003,14 @@ static int do_flock(struct file *file, int cmd, struct file_lock *fl)
gfs2_holder_init(gl, state, flags, fl_gh);
gfs2_glock_put(gl);
}
error = gfs2_glock_nq(fl_gh);
for (sleeptime = 1; sleeptime <= 4; sleeptime <<= 1) {
error = gfs2_glock_nq(fl_gh);
if (error != GLR_TRYFAILED)
break;
fl_gh->gh_flags = LM_FLAG_TRY | GL_EXACT;
fl_gh->gh_error = 0;
msleep(sleeptime);
}
if (error) {
gfs2_holder_uninit(fl_gh);
if (error == GLR_TRYFAILED)
@ -1024,7 +1033,7 @@ static void do_unflock(struct file *file, struct file_lock *fl)
mutex_lock(&fp->f_fl_mutex);
flock_lock_file_wait(file, fl);
if (fl_gh->gh_gl) {
gfs2_glock_dq_wait(fl_gh);
gfs2_glock_dq(fl_gh);
gfs2_holder_uninit(fl_gh);
}
mutex_unlock(&fp->f_fl_mutex);