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Date: Thu, 27 Nov 2014 19:34:10 +0100
From: Loïc Pefferkorn <loic@...cp.eu>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: oleg.drokin@...el.com, andreas.dilger@...el.com, gdonald@...il.com,
keith.mannthey@...el.com, john.hammond@...el.com,
devel@...verdev.osuosl.org, HPDD-discuss@...ts.01.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: lustre: fix sparse warnings related to lock
context imbalance
Hello Greg,
After some investigation, I think that removing these wrappers is not going to improve the code readability:
On Wed, Nov 26, 2014 at 12:54:43PM -0800, Greg KH wrote:
> On Wed, Nov 26, 2014 at 05:15:48PM +0100, Loic Pefferkorn wrote:
> > Add __acquires() and __releases() function annotations, to fix sparse warnings related to lock context imbalance.
> >
> > This fixes the following warnings:
> >
> > drivers/staging/lustre/lustre/libcfs/linux/linux-tracefile.c:153:5: warning: context imbalance in 'cfs_trace_lock_tcd' - wrong count at exit
> > drivers/staging/lustre/lustre/libcfs/hash.c:128:1: warning: context imbalance in 'cfs_hash_spin_lock' - wrong count at exit
> > drivers/staging/lustre/lustre/libcfs/hash.c:142:9: warning: context imbalance in 'cfs_hash_rw_lock' - wrong count at exit
> > drivers/staging/lustre/lustre/ptlrpc/../../lustre/ldlm/l_lock.c:57:17: warning: context imbalance in 'lock_res_and_lock' - wrong count at exit
> > drivers/staging/lustre/lustre/libcfs/libcfs_lock.c:93:1: warning: context imbalance in 'cfs_percpt_lock' - wrong count at exit
> >
> > Signed-off-by: Loic Pefferkorn <loic@...cp.eu>
> > ---
> > drivers/staging/lustre/lustre/libcfs/hash.c | 4 ++++
> > drivers/staging/lustre/lustre/libcfs/libcfs_lock.c | 2 ++
> > drivers/staging/lustre/lustre/libcfs/linux/linux-tracefile.c | 2 ++
> > drivers/staging/lustre/lustre/obdclass/cl_object.c | 2 ++
> > 4 files changed, 10 insertions(+)
> >
> > diff --git a/drivers/staging/lustre/lustre/libcfs/hash.c b/drivers/staging/lustre/lustre/libcfs/hash.c
> > index 32da783..7c6e2a3 100644
> > --- a/drivers/staging/lustre/lustre/libcfs/hash.c
> > +++ b/drivers/staging/lustre/lustre/libcfs/hash.c
> > @@ -126,18 +126,21 @@ cfs_hash_nl_unlock(union cfs_hash_lock *lock, int exclusive) {}
> >
> > static inline void
> > cfs_hash_spin_lock(union cfs_hash_lock *lock, int exclusive)
> > + __acquires(&lock->spin)
> > {
> > spin_lock(&lock->spin);
> > }
> >
> > static inline void
> > cfs_hash_spin_unlock(union cfs_hash_lock *lock, int exclusive)
> > + __releases(&lock->spin)
> > {
> > spin_unlock(&lock->spin);
> > }
>
> Ugh, how horrid, please just delete these functions and push down the
> spin_lock/unlock calls down into the places these are called.
cfs_hash_spin_lock() and cfs_hash_spin_unlock() are referenced by function pointers later in the same file:
165 /** no bucket lock, one spinlock to protect everything */
166 static cfs_hash_lock_ops_t cfs_hash_nbl_lops = {
167 .hs_lock = cfs_hash_spin_lock,
168 .hs_unlock = cfs_hash_spin_unlock,
169 .hs_bkt_lock = cfs_hash_nl_lock,
170 .hs_bkt_unlock = cfs_hash_nl_unlock,
171 };
172
173 /** spin bucket lock, rehash is enabled */
174 static cfs_hash_lock_ops_t cfs_hash_bkt_spin_lops = {
175 .hs_lock = cfs_hash_rw_lock,
176 .hs_unlock = cfs_hash_rw_unlock,
177 .hs_bkt_lock = cfs_hash_spin_lock,
178 .hs_bkt_unlock = cfs_hash_spin_unlock,
179 };
>
> >
> > static inline void
> > cfs_hash_rw_lock(union cfs_hash_lock *lock, int exclusive)
> > + __acquires(&lock->rw)
> > {
> > if (!exclusive)
> > read_lock(&lock->rw);
> > @@ -147,6 +150,7 @@ cfs_hash_rw_lock(union cfs_hash_lock *lock, int exclusive)
> >
> > static inline void
> > cfs_hash_rw_unlock(union cfs_hash_lock *lock, int exclusive)
> > + __releases(&lock->rw)
> > {
> > if (!exclusive)
> > read_unlock(&lock->rw);
>
>
> Same for these.
Likewise for cfs_hash_rw_lock() and cfs_hash_rw_unlock():
173 /** spin bucket lock, rehash is enabled */
174 static cfs_hash_lock_ops_t cfs_hash_bkt_spin_lops = {
175 .hs_lock = cfs_hash_rw_lock,
176 .hs_unlock = cfs_hash_rw_unlock,
177 .hs_bkt_lock = cfs_hash_spin_lock,
178 .hs_bkt_unlock = cfs_hash_spin_unlock,
179 };
180
181 /** rw bucket lock, rehash is enabled */
182 static cfs_hash_lock_ops_t cfs_hash_bkt_rw_lops = {
183 .hs_lock = cfs_hash_rw_lock,
184 .hs_unlock = cfs_hash_rw_unlock,
185 .hs_bkt_lock = cfs_hash_rw_lock,
186 .hs_bkt_unlock = cfs_hash_rw_unlock,
187 };
>
> > diff --git a/drivers/staging/lustre/lustre/libcfs/libcfs_lock.c b/drivers/staging/lustre/lustre/libcfs/libcfs_lock.c
> > index 2c199c7..1e529fc 100644
> > --- a/drivers/staging/lustre/lustre/libcfs/libcfs_lock.c
> > +++ b/drivers/staging/lustre/lustre/libcfs/libcfs_lock.c
> > @@ -91,6 +91,7 @@ EXPORT_SYMBOL(cfs_percpt_lock_alloc);
> > */
> > void
> > cfs_percpt_lock(struct cfs_percpt_lock *pcl, int index)
> > + __acquires(pcl->pcl_locks[index])
> > {
> > int ncpt = cfs_cpt_number(pcl->pcl_cptab);
> > int i;
> > @@ -125,6 +126,7 @@ EXPORT_SYMBOL(cfs_percpt_lock);
> > /** unlock a CPU partition */
> > void
> > cfs_percpt_unlock(struct cfs_percpt_lock *pcl, int index)
> > + __releases(pcl->pcl_locks[index])
> > {
> > int ncpt = cfs_cpt_number(pcl->pcl_cptab);
> > int i;
> > diff --git a/drivers/staging/lustre/lustre/libcfs/linux/linux-tracefile.c b/drivers/staging/lustre/lustre/libcfs/linux/linux-tracefile.c
> > index 976c61e..257669b 100644
> > --- a/drivers/staging/lustre/lustre/libcfs/linux/linux-tracefile.c
> > +++ b/drivers/staging/lustre/lustre/libcfs/linux/linux-tracefile.c
> > @@ -151,6 +151,7 @@ cfs_trace_buf_type_t cfs_trace_buf_idx_get(void)
> > * for details.
> > */
> > int cfs_trace_lock_tcd(struct cfs_trace_cpu_data *tcd, int walking)
> > + __acquires(&tcd->tc_lock)
> > {
> > __LASSERT(tcd->tcd_type < CFS_TCD_TYPE_MAX);
> > if (tcd->tcd_type == CFS_TCD_TYPE_IRQ)
> > @@ -165,6 +166,7 @@ int cfs_trace_lock_tcd(struct cfs_trace_cpu_data *tcd, int walking)
> > }
> >
> > void cfs_trace_unlock_tcd(struct cfs_trace_cpu_data *tcd, int walking)
> > + __releases(&tcd->tcd_lock)
> > {
> > __LASSERT(tcd->tcd_type < CFS_TCD_TYPE_MAX);
> > if (tcd->tcd_type == CFS_TCD_TYPE_IRQ)
> > diff --git a/drivers/staging/lustre/lustre/obdclass/cl_object.c b/drivers/staging/lustre/lustre/obdclass/cl_object.c
> > index ce96bd2..8577f97 100644
> > --- a/drivers/staging/lustre/lustre/obdclass/cl_object.c
> > +++ b/drivers/staging/lustre/lustre/obdclass/cl_object.c
> > @@ -193,6 +193,7 @@ static spinlock_t *cl_object_attr_guard(struct cl_object *o)
> > * cl_object_attr_get(), cl_object_attr_set().
> > */
> > void cl_object_attr_lock(struct cl_object *o)
> > + __acquires(cl_object_attr_guard(o))
> > {
> > spin_lock(cl_object_attr_guard(o));
> > }
> > @@ -202,6 +203,7 @@ EXPORT_SYMBOL(cl_object_attr_lock);
> > * Releases data-attributes lock, acquired by cl_object_attr_lock().
> > */
> > void cl_object_attr_unlock(struct cl_object *o)
> > + __releases(cl_object_attr_guard(o))
> > {
> > spin_unlock(cl_object_attr_guard(o));
> > }
>
> Same thing here.
These ones are easy to replace, but the naming scheme of all functions in cl_object.c is consistent,
from my point of view it ease code reading where they are called, for example in lustre/lustre/osc/osc_request.c:
before:
1827 if (valid != 0) {
1828 cl_object_attr_lock(obj);
1829 cl_object_attr_set(env, obj, attr, valid);
1830 cl_object_attr_unlock(obj);
after:
1827 if (valid != 0) {
1828 spin_lock(cl_object_attr_guard(obj));
1829 cl_object_attr_set(env, obj, attr, valid);
1830 spin_unlock(cl_object_attr_guard(obj));
But I'm here for learning, and I would be grateful to have your opinion.
--
Cheers,
Loic
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