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dlm: move lkb xarray lookup out of lock

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This patch moves the xarray lookup functionality for the lkb out of the
ls_lkbxa_lock read lock handling. We can do that as the xarray should be
possible to access lockless in case of reader like xa_load(). We confirm
under ls_lkbxa_lock that the lkb is still part of the data structure and
take a reference when its still part of ls_lkbxa to avoid being freed
after doing the lookup. To do a check if the lkb is still part of the
ls_lkbxa data structure we use a kref_read() as the last put will remove
it from the ls_lkbxa data structure and any reference taken means it is
still part of ls_lkbxa.

A similar approach was done with the DLM rsb rhashtable just with a flag
instead of the refcounter because the refcounter has a slightly
different meaning.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>
This commit is contained in:
Alexander Aring 2024-08-02 13:26:46 -04:00 committed by David Teigland
parent 5be323b0c6
commit c846f732b9
3 changed files with 23 additions and 5 deletions
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1
fs/dlm/dlm_internal.h
View File

@ -295,6 +295,7 @@ struct dlm_lkb {
void *lkb_astparam; /* caller's ast arg */
struct dlm_user_args *lkb_ua;
};
struct rcu_head rcu;
};
/*

18
fs/dlm/lock.c
View File

@ -1527,11 +1527,21 @@ static int find_lkb(struct dlm_ls *ls, uint32_t lkid, struct dlm_lkb **lkb_ret)
{
struct dlm_lkb *lkb;
read_lock_bh(&ls->ls_lkbxa_lock);
rcu_read_lock();
lkb = xa_load(&ls->ls_lkbxa, lkid);
if (lkb)
kref_get(&lkb->lkb_ref);
read_unlock_bh(&ls->ls_lkbxa_lock);
if (lkb) {
/* check if lkb is still part of lkbxa under lkbxa_lock as
* the lkb_ref is tight to the lkbxa data structure, see
* __put_lkb().
*/
read_lock_bh(&ls->ls_lkbxa_lock);
if (kref_read(&lkb->lkb_ref))
kref_get(&lkb->lkb_ref);
else
lkb = NULL;
read_unlock_bh(&ls->ls_lkbxa_lock);
}
rcu_read_unlock();
*lkb_ret = lkb;
return lkb ? 0 : -ENOENT;

9
fs/dlm/memory.c
View File

@ -115,8 +115,10 @@ struct dlm_lkb *dlm_allocate_lkb(void)
return kmem_cache_zalloc(lkb_cache, GFP_ATOMIC);
}
void dlm_free_lkb(struct dlm_lkb *lkb)
static void __free_lkb_rcu(struct rcu_head *rcu)
{
struct dlm_lkb *lkb = container_of(rcu, struct dlm_lkb, rcu);
if (test_bit(DLM_DFL_USER_BIT, &lkb->lkb_dflags)) {
struct dlm_user_args *ua;
ua = lkb->lkb_ua;
@ -129,6 +131,11 @@ void dlm_free_lkb(struct dlm_lkb *lkb)
kmem_cache_free(lkb_cache, lkb);
}
void dlm_free_lkb(struct dlm_lkb *lkb)
{
call_rcu(&lkb->rcu, __free_lkb_rcu);
}
struct dlm_mhandle *dlm_allocate_mhandle(void)
{
return kmem_cache_alloc(mhandle_cache, GFP_ATOMIC);