| Message ID | 173006668387.81717.13494809143579612819@noble.neil.brown.name (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | nfsd: make use of warning provided by refcount_t | expand |
On Mon, 2024-10-28 at 09:04 +1100, NeilBrown wrote: > refcount_t, by design, checks for unwanted situations and provides > warnings. It is rarely useful to have explicit warnings with refcount > usage. > > In this case we have an explicit warning if a refcount_t reaches zero > when decremented. Simply using refcount_dec() will provide a similar > warning and also mark the refcount_t as saturated to avoid any possible > use-after-free. > > This patch drops the warning and uses refcount_dec() instead of > refcount_dec_and_test(). > > Signed-off-by: NeilBrown <neilb@suse.de> > --- > fs/nfsd/filecache.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > index 1408166222c5..c16671135d17 100644 > --- a/fs/nfsd/filecache.c > +++ b/fs/nfsd/filecache.c > @@ -1050,7 +1050,7 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct net *net, > * the last one however, since we should hold another. > */ > if (nfsd_file_lru_remove(nf)) > - WARN_ON_ONCE(refcount_dec_and_test(&nf->nf_ref)); > + refcount_dec(&nf->nf_ref); The existing code threw a warning when the counter reached 0. Your change will make the potential warning fire later, after we try to put the last reference and the counter goes to -1. That's probably fine as it should happen later in this function either way. > goto wait_for_construction; > } > > > base-commit: 7fa861d5df402b2327f45e0240c1b842f71fec11 Reviewed-by: Jeff Layton <jlayton@kernel.org>
On Tue, 29 Oct 2024, Jeff Layton wrote: > On Mon, 2024-10-28 at 09:04 +1100, NeilBrown wrote: > > refcount_t, by design, checks for unwanted situations and provides > > warnings. It is rarely useful to have explicit warnings with refcount > > usage. > > > > In this case we have an explicit warning if a refcount_t reaches zero > > when decremented. Simply using refcount_dec() will provide a similar > > warning and also mark the refcount_t as saturated to avoid any possible > > use-after-free. > > > > This patch drops the warning and uses refcount_dec() instead of > > refcount_dec_and_test(). > > > > Signed-off-by: NeilBrown <neilb@suse.de> > > --- > > fs/nfsd/filecache.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > > index 1408166222c5..c16671135d17 100644 > > --- a/fs/nfsd/filecache.c > > +++ b/fs/nfsd/filecache.c > > @@ -1050,7 +1050,7 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct net *net, > > * the last one however, since we should hold another. > > */ > > if (nfsd_file_lru_remove(nf)) > > - WARN_ON_ONCE(refcount_dec_and_test(&nf->nf_ref)); > > + refcount_dec(&nf->nf_ref); > > The existing code threw a warning when the counter reached 0. Your > change will make the potential warning fire later, after we try to put > the last reference and the counter goes to -1. That's probably fine as > it should happen later in this function either way. The code in refcount_dec() contains: if (unlikely(old <= 1)) refcount_warn_saturate(r, REFCOUNT_DEC_LEAK); NeilBrown > > > goto wait_for_construction; > > } > > > > > > base-commit: 7fa861d5df402b2327f45e0240c1b842f71fec11 > > Reviewed-by: Jeff Layton <jlayton@kernel.org> >
On Tue, 2024-10-29 at 07:47 +1100, NeilBrown wrote: > On Tue, 29 Oct 2024, Jeff Layton wrote: > > On Mon, 2024-10-28 at 09:04 +1100, NeilBrown wrote: > > > refcount_t, by design, checks for unwanted situations and provides > > > warnings. It is rarely useful to have explicit warnings with refcount > > > usage. > > > > > > In this case we have an explicit warning if a refcount_t reaches zero > > > when decremented. Simply using refcount_dec() will provide a similar > > > warning and also mark the refcount_t as saturated to avoid any possible > > > use-after-free. > > > > > > This patch drops the warning and uses refcount_dec() instead of > > > refcount_dec_and_test(). > > > > > > Signed-off-by: NeilBrown <neilb@suse.de> > > > --- > > > fs/nfsd/filecache.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > > > index 1408166222c5..c16671135d17 100644 > > > --- a/fs/nfsd/filecache.c > > > +++ b/fs/nfsd/filecache.c > > > @@ -1050,7 +1050,7 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct net *net, > > > * the last one however, since we should hold another. > > > */ > > > if (nfsd_file_lru_remove(nf)) > > > - WARN_ON_ONCE(refcount_dec_and_test(&nf->nf_ref)); > > > + refcount_dec(&nf->nf_ref); > > > > The existing code threw a warning when the counter reached 0. Your > > change will make the potential warning fire later, after we try to put > > the last reference and the counter goes to -1. That's probably fine as > > it should happen later in this function either way. > > The code in refcount_dec() contains: > > if (unlikely(old <= 1)) > refcount_warn_saturate(r, REFCOUNT_DEC_LEAK); > > I stand corrected! I thought it only fired once it went below 0, but I guess in this case, it does it on a 0->1 transition since this is a refcount_dec() (sans "test"). > > > > > goto wait_for_construction; > > > } > > > > > > > > > base-commit: 7fa861d5df402b2327f45e0240c1b842f71fec11 > > > > Reviewed-by: Jeff Layton <jlayton@kernel.org> > > >
From: Chuck Lever <chuck.lever@oracle.com> On Mon, 28 Oct 2024 09:04:43 +1100, NeilBrown wrote: > refcount_t, by design, checks for unwanted situations and provides > warnings. It is rarely useful to have explicit warnings with refcount > usage. > > In this case we have an explicit warning if a refcount_t reaches zero > when decremented. Simply using refcount_dec() will provide a similar > warning and also mark the refcount_t as saturated to avoid any possible > use-after-free. > > [...] Applied to nfsd-next for v6.13, thanks! [1/1] nfsd: make use of warning provided by refcount_t commit: 74ca1dc05e0448b248ae3f2be07d716f4938d0fc -- Chuck Lever
diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c index 1408166222c5..c16671135d17 100644 --- a/fs/nfsd/filecache.c +++ b/fs/nfsd/filecache.c @@ -1050,7 +1050,7 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct net *net, * the last one however, since we should hold another. */ if (nfsd_file_lru_remove(nf)) - WARN_ON_ONCE(refcount_dec_and_test(&nf->nf_ref)); + refcount_dec(&nf->nf_ref); goto wait_for_construction; }
refcount_t, by design, checks for unwanted situations and provides warnings. It is rarely useful to have explicit warnings with refcount usage. In this case we have an explicit warning if a refcount_t reaches zero when decremented. Simply using refcount_dec() will provide a similar warning and also mark the refcount_t as saturated to avoid any possible use-after-free. This patch drops the warning and uses refcount_dec() instead of refcount_dec_and_test(). Signed-off-by: NeilBrown <neilb@suse.de> --- fs/nfsd/filecache.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) base-commit: 7fa861d5df402b2327f45e0240c1b842f71fec11