* [PATCH] fs/dax: Fix pmd vs pte conflict detection
@ 2019-10-19 16:26 Dan Williams
2019-10-19 20:50 ` Matthew Wilcox
` (2 more replies)
0 siblings, 3 replies; 7+ messages in thread
From: Dan Williams @ 2019-10-19 16:26 UTC (permalink / raw)
To: linux-fsdevel
Cc: Jeff Smits, Doug Nelson, stable, Jan Kara,
Matthew Wilcox (Oracle),
linux-nvdimm, linux-kernel
Check for NULL entries before checking the entry order, otherwise NULL
is misinterpreted as a present pte conflict. The 'order' check needs to
happen before the locked check as an unlocked entry at the wrong order
must fallback to lookup the correct order.
Reported-by: Jeff Smits <jeff.smits@intel.com>
Reported-by: Doug Nelson <doug.nelson@intel.com>
Cc: <stable@vger.kernel.org>
Fixes: 23c84eb78375 ("dax: Fix missed wakeup with PMD faults")
Cc: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
fs/dax.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index a71881e77204..08160011d94c 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -221,10 +221,11 @@ static void *get_unlocked_entry(struct xa_state *xas, unsigned int order)
for (;;) {
entry = xas_find_conflict(xas);
+ if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
+ return entry;
if (dax_entry_order(entry) < order)
return XA_RETRY_ENTRY;
- if (!entry || WARN_ON_ONCE(!xa_is_value(entry)) ||
- !dax_is_locked(entry))
+ if (!dax_is_locked(entry))
return entry;
wq = dax_entry_waitqueue(xas, entry, &ewait.key);
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] fs/dax: Fix pmd vs pte conflict detection
2019-10-19 16:26 [PATCH] fs/dax: Fix pmd vs pte conflict detection Dan Williams
@ 2019-10-19 20:50 ` Matthew Wilcox
2019-10-19 23:09 ` Dan Williams
2019-10-21 8:47 ` Jan Kara
2019-10-21 12:07 ` Jeff Moyer
2 siblings, 1 reply; 7+ messages in thread
From: Matthew Wilcox @ 2019-10-19 20:50 UTC (permalink / raw)
To: Dan Williams
Cc: linux-fsdevel, Jeff Smits, Doug Nelson, stable, Jan Kara,
linux-nvdimm, linux-kernel
On Sat, Oct 19, 2019 at 09:26:19AM -0700, Dan Williams wrote:
> Check for NULL entries before checking the entry order, otherwise NULL
> is misinterpreted as a present pte conflict. The 'order' check needs to
> happen before the locked check as an unlocked entry at the wrong order
> must fallback to lookup the correct order.
>
> Reported-by: Jeff Smits <jeff.smits@intel.com>
> Reported-by: Doug Nelson <doug.nelson@intel.com>
> Cc: <stable@vger.kernel.org>
> Fixes: 23c84eb78375 ("dax: Fix missed wakeup with PMD faults")
> Cc: Jan Kara <jack@suse.cz>
> Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> fs/dax.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index a71881e77204..08160011d94c 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -221,10 +221,11 @@ static void *get_unlocked_entry(struct xa_state *xas, unsigned int order)
>
> for (;;) {
> entry = xas_find_conflict(xas);
> + if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
> + return entry;
> if (dax_entry_order(entry) < order)
> return XA_RETRY_ENTRY;
> - if (!entry || WARN_ON_ONCE(!xa_is_value(entry)) ||
> - !dax_is_locked(entry))
> + if (!dax_is_locked(entry))
> return entry;
Yes, I think this works. Should we also add:
static unsigned int dax_entry_order(void *entry)
{
+ BUG_ON(!xa_is_value(entry));
if (xa_to_value(entry) & DAX_PMD)
return PMD_ORDER;
return 0;
}
which would have caught this logic error before it caused a performance
regression?
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] fs/dax: Fix pmd vs pte conflict detection
2019-10-19 20:50 ` Matthew Wilcox
@ 2019-10-19 23:09 ` Dan Williams
2019-10-19 23:27 ` Dan Williams
0 siblings, 1 reply; 7+ messages in thread
From: Dan Williams @ 2019-10-19 23:09 UTC (permalink / raw)
To: Matthew Wilcox
Cc: linux-fsdevel, Jeff Smits, Doug Nelson, stable, Jan Kara,
linux-nvdimm, Linux Kernel Mailing List
On Sat, Oct 19, 2019 at 1:50 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Sat, Oct 19, 2019 at 09:26:19AM -0700, Dan Williams wrote:
> > Check for NULL entries before checking the entry order, otherwise NULL
> > is misinterpreted as a present pte conflict. The 'order' check needs to
> > happen before the locked check as an unlocked entry at the wrong order
> > must fallback to lookup the correct order.
> >
> > Reported-by: Jeff Smits <jeff.smits@intel.com>
> > Reported-by: Doug Nelson <doug.nelson@intel.com>
> > Cc: <stable@vger.kernel.org>
> > Fixes: 23c84eb78375 ("dax: Fix missed wakeup with PMD faults")
> > Cc: Jan Kara <jack@suse.cz>
> > Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> > ---
> > fs/dax.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/dax.c b/fs/dax.c
> > index a71881e77204..08160011d94c 100644
> > --- a/fs/dax.c
> > +++ b/fs/dax.c
> > @@ -221,10 +221,11 @@ static void *get_unlocked_entry(struct xa_state *xas, unsigned int order)
> >
> > for (;;) {
> > entry = xas_find_conflict(xas);
> > + if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
> > + return entry;
> > if (dax_entry_order(entry) < order)
> > return XA_RETRY_ENTRY;
> > - if (!entry || WARN_ON_ONCE(!xa_is_value(entry)) ||
> > - !dax_is_locked(entry))
> > + if (!dax_is_locked(entry))
> > return entry;
>
> Yes, I think this works. Should we also add:
>
> static unsigned int dax_entry_order(void *entry)
> {
> + BUG_ON(!xa_is_value(entry));
> if (xa_to_value(entry) & DAX_PMD)
> return PMD_ORDER;
> return 0;
> }
>
> which would have caught this logic error before it caused a performance
> regression?
Sounds good will add it to v2.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] fs/dax: Fix pmd vs pte conflict detection
2019-10-19 23:09 ` Dan Williams
@ 2019-10-19 23:27 ` Dan Williams
0 siblings, 0 replies; 7+ messages in thread
From: Dan Williams @ 2019-10-19 23:27 UTC (permalink / raw)
To: Matthew Wilcox
Cc: linux-fsdevel, Jeff Smits, Doug Nelson, stable, Jan Kara,
linux-nvdimm, Linux Kernel Mailing List
On Sat, Oct 19, 2019 at 4:09 PM Dan Williams <dan.j.williams@intel.com> wrote:
>
> On Sat, Oct 19, 2019 at 1:50 PM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Sat, Oct 19, 2019 at 09:26:19AM -0700, Dan Williams wrote:
> > > Check for NULL entries before checking the entry order, otherwise NULL
> > > is misinterpreted as a present pte conflict. The 'order' check needs to
> > > happen before the locked check as an unlocked entry at the wrong order
> > > must fallback to lookup the correct order.
> > >
> > > Reported-by: Jeff Smits <jeff.smits@intel.com>
> > > Reported-by: Doug Nelson <doug.nelson@intel.com>
> > > Cc: <stable@vger.kernel.org>
> > > Fixes: 23c84eb78375 ("dax: Fix missed wakeup with PMD faults")
> > > Cc: Jan Kara <jack@suse.cz>
> > > Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> > > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> > > ---
> > > fs/dax.c | 5 +++--
> > > 1 file changed, 3 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/dax.c b/fs/dax.c
> > > index a71881e77204..08160011d94c 100644
> > > --- a/fs/dax.c
> > > +++ b/fs/dax.c
> > > @@ -221,10 +221,11 @@ static void *get_unlocked_entry(struct xa_state *xas, unsigned int order)
> > >
> > > for (;;) {
> > > entry = xas_find_conflict(xas);
> > > + if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
> > > + return entry;
> > > if (dax_entry_order(entry) < order)
> > > return XA_RETRY_ENTRY;
> > > - if (!entry || WARN_ON_ONCE(!xa_is_value(entry)) ||
> > > - !dax_is_locked(entry))
> > > + if (!dax_is_locked(entry))
> > > return entry;
> >
> > Yes, I think this works. Should we also add:
> >
> > static unsigned int dax_entry_order(void *entry)
> > {
> > + BUG_ON(!xa_is_value(entry));
> > if (xa_to_value(entry) & DAX_PMD)
> > return PMD_ORDER;
> > return 0;
> > }
> >
> > which would have caught this logic error before it caused a performance
> > regression?
>
> Sounds good will add it to v2.
...except that there are multiple dax helpers that have the 'value'
entry assumption. I'd rather do all of them in a separate patch, or
none of them. It turns out that after this change all
dax_entry_order() invocations are now protected by a xa_is_value()
assert earlier in the calling function.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] fs/dax: Fix pmd vs pte conflict detection
2019-10-19 16:26 [PATCH] fs/dax: Fix pmd vs pte conflict detection Dan Williams
2019-10-19 20:50 ` Matthew Wilcox
@ 2019-10-21 8:47 ` Jan Kara
2019-10-21 12:07 ` Jeff Moyer
2 siblings, 0 replies; 7+ messages in thread
From: Jan Kara @ 2019-10-21 8:47 UTC (permalink / raw)
To: Dan Williams
Cc: linux-fsdevel, Jeff Smits, Doug Nelson, stable, Jan Kara,
Matthew Wilcox (Oracle),
linux-nvdimm, linux-kernel
On Sat 19-10-19 09:26:19, Dan Williams wrote:
> Check for NULL entries before checking the entry order, otherwise NULL
> is misinterpreted as a present pte conflict. The 'order' check needs to
> happen before the locked check as an unlocked entry at the wrong order
> must fallback to lookup the correct order.
>
> Reported-by: Jeff Smits <jeff.smits@intel.com>
> Reported-by: Doug Nelson <doug.nelson@intel.com>
> Cc: <stable@vger.kernel.org>
> Fixes: 23c84eb78375 ("dax: Fix missed wakeup with PMD faults")
> Cc: Jan Kara <jack@suse.cz>
> Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Good catch! The patch looks good to me. You can add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> fs/dax.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index a71881e77204..08160011d94c 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -221,10 +221,11 @@ static void *get_unlocked_entry(struct xa_state *xas, unsigned int order)
>
> for (;;) {
> entry = xas_find_conflict(xas);
> + if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
> + return entry;
> if (dax_entry_order(entry) < order)
> return XA_RETRY_ENTRY;
> - if (!entry || WARN_ON_ONCE(!xa_is_value(entry)) ||
> - !dax_is_locked(entry))
> + if (!dax_is_locked(entry))
> return entry;
>
> wq = dax_entry_waitqueue(xas, entry, &ewait.key);
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] fs/dax: Fix pmd vs pte conflict detection
2019-10-19 16:26 [PATCH] fs/dax: Fix pmd vs pte conflict detection Dan Williams
2019-10-19 20:50 ` Matthew Wilcox
2019-10-21 8:47 ` Jan Kara
@ 2019-10-21 12:07 ` Jeff Moyer
2019-10-21 14:44 ` Dan Williams
2 siblings, 1 reply; 7+ messages in thread
From: Jeff Moyer @ 2019-10-21 12:07 UTC (permalink / raw)
To: Dan Williams
Cc: linux-fsdevel, Jeff Smits, Doug Nelson, stable, Jan Kara,
Matthew Wilcox (Oracle),
linux-nvdimm, linux-kernel
Dan Williams <dan.j.williams@intel.com> writes:
> Check for NULL entries before checking the entry order, otherwise NULL
> is misinterpreted as a present pte conflict. The 'order' check needs to
> happen before the locked check as an unlocked entry at the wrong order
> must fallback to lookup the correct order.
Please include the user-visible effects of the problem in the changelog.
Thanks,
Jeff
>
> Reported-by: Jeff Smits <jeff.smits@intel.com>
> Reported-by: Doug Nelson <doug.nelson@intel.com>
> Cc: <stable@vger.kernel.org>
> Fixes: 23c84eb78375 ("dax: Fix missed wakeup with PMD faults")
> Cc: Jan Kara <jack@suse.cz>
> Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> fs/dax.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index a71881e77204..08160011d94c 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -221,10 +221,11 @@ static void *get_unlocked_entry(struct xa_state *xas, unsigned int order)
>
> for (;;) {
> entry = xas_find_conflict(xas);
> + if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
> + return entry;
> if (dax_entry_order(entry) < order)
> return XA_RETRY_ENTRY;
> - if (!entry || WARN_ON_ONCE(!xa_is_value(entry)) ||
> - !dax_is_locked(entry))
> + if (!dax_is_locked(entry))
> return entry;
>
> wq = dax_entry_waitqueue(xas, entry, &ewait.key);
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] fs/dax: Fix pmd vs pte conflict detection
2019-10-21 12:07 ` Jeff Moyer
@ 2019-10-21 14:44 ` Dan Williams
0 siblings, 0 replies; 7+ messages in thread
From: Dan Williams @ 2019-10-21 14:44 UTC (permalink / raw)
To: Jeff Moyer
Cc: linux-fsdevel, Jeff Smits, Doug Nelson, stable, Jan Kara,
Matthew Wilcox (Oracle),
linux-nvdimm, Linux Kernel Mailing List
On Mon, Oct 21, 2019 at 5:07 AM Jeff Moyer <jmoyer@redhat.com> wrote:
>
> Dan Williams <dan.j.williams@intel.com> writes:
>
> > Check for NULL entries before checking the entry order, otherwise NULL
> > is misinterpreted as a present pte conflict. The 'order' check needs to
> > happen before the locked check as an unlocked entry at the wrong order
> > must fallback to lookup the correct order.
>
> Please include the user-visible effects of the problem in the changelog.
>
Yup, I noticed that right after sending.
^ permalink raw reply [flat|nested] 7+ messages in thread
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2019-10-19 16:26 [PATCH] fs/dax: Fix pmd vs pte conflict detection Dan Williams
2019-10-19 20:50 ` Matthew Wilcox
2019-10-19 23:09 ` Dan Williams
2019-10-19 23:27 ` Dan Williams
2019-10-21 8:47 ` Jan Kara
2019-10-21 12:07 ` Jeff Moyer
2019-10-21 14:44 ` Dan Williams
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