| Message ID | 20191206135316.47703-14-steven.price@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Generic page walk and ptdump | expand |
Hi Steven,
I love your patch! Perhaps something to improve:
[auto build test WARNING on linus/master]
[also build test WARNING on v5.5-rc1 next-20191209]
[cannot apply to arm64/for-next/core tip/x86/mm]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]
url: https://github.com/0day-ci/linux/commits/Steven-Price/Generic-page-walk-and-ptdump/20191208-035831
base: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git ad910e36da4ca3a1bd436989f632d062dda0c921
reproduce:
# apt-get install sparse
# sparse version: v0.6.1-101-g82dee2e-dirty
make ARCH=x86_64 allmodconfig
make C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'
If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>
sparse warnings: (new ones prefixed by >>)
>> include/linux/spinlock.h:378:9: sparse: sparse: context imbalance in 'walk_pte_range' - unexpected unlock
vim +/walk_pte_range +378 include/linux/spinlock.h
c2f21ce2e31286 Thomas Gleixner 2009-12-02 375
3490565b633c70 Denys Vlasenko 2015-07-13 376 static __always_inline void spin_unlock(spinlock_t *lock)
c2f21ce2e31286 Thomas Gleixner 2009-12-02 377 {
c2f21ce2e31286 Thomas Gleixner 2009-12-02 @378 raw_spin_unlock(&lock->rlock);
c2f21ce2e31286 Thomas Gleixner 2009-12-02 379 }
c2f21ce2e31286 Thomas Gleixner 2009-12-02 380
:::::: The code at line 378 was first introduced by commit
:::::: c2f21ce2e31286a0a32f8da0a7856e9ca1122ef3 locking: Implement new raw_spinlock
:::::: TO: Thomas Gleixner <tglx@linutronix.de>
:::::: CC: Thomas Gleixner <tglx@linutronix.de>
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org Intel Corporation
On 10/12/2019 11:23, kbuild test robot wrote: > Hi Steven, > > I love your patch! Perhaps something to improve: > > [auto build test WARNING on linus/master] > [also build test WARNING on v5.5-rc1 next-20191209] > [cannot apply to arm64/for-next/core tip/x86/mm] > [if your patch is applied to the wrong git tree, please drop us a note to help > improve the system. BTW, we also suggest to use '--base' option to specify the > base tree in git format-patch, please see https://stackoverflow.com/a/37406982] > > url: https://github.com/0day-ci/linux/commits/Steven-Price/Generic-page-walk-and-ptdump/20191208-035831 > base: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git ad910e36da4ca3a1bd436989f632d062dda0c921 > reproduce: > # apt-get install sparse > # sparse version: v0.6.1-101-g82dee2e-dirty > make ARCH=x86_64 allmodconfig > make C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' > > If you fix the issue, kindly add following tag > Reported-by: kbuild test robot <lkp@intel.com> > > > sparse warnings: (new ones prefixed by >>) > >>> include/linux/spinlock.h:378:9: sparse: sparse: context imbalance in 'walk_pte_range' - unexpected unlock I believe this is a false positive (although the trace here is useless). This patch adds a conditional lock/unlock: pte = walk->no_vma ? pte_offset_map(pmd, addr) : pte_offset_map_lock(walk->mm, pmd, addr, &ptl); ... if (!walk->no_vma) spin_unlock(ptl); pte_unmap(pte); I'm not sure how to match sparse happy about that. Is the only option to have two versions of the walk_pte_range() function? One which takes the lock and one which doesn't. Steve > vim +/walk_pte_range +378 include/linux/spinlock.h > > c2f21ce2e31286 Thomas Gleixner 2009-12-02 375 > 3490565b633c70 Denys Vlasenko 2015-07-13 376 static __always_inline void spin_unlock(spinlock_t *lock) > c2f21ce2e31286 Thomas Gleixner 2009-12-02 377 { > c2f21ce2e31286 Thomas Gleixner 2009-12-02 @378 raw_spin_unlock(&lock->rlock); > c2f21ce2e31286 Thomas Gleixner 2009-12-02 379 } > c2f21ce2e31286 Thomas Gleixner 2009-12-02 380 > > :::::: The code at line 378 was first introduced by commit > :::::: c2f21ce2e31286a0a32f8da0a7856e9ca1122ef3 locking: Implement new raw_spinlock > > :::::: TO: Thomas Gleixner <tglx@linutronix.de> > :::::: CC: Thomas Gleixner <tglx@linutronix.de> > > --- > 0-DAY kernel test infrastructure Open Source Technology Center > https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org Intel Corporation > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >
On Wed, Dec 11, 2019 at 03:54:06PM +0000, Steven Price wrote: > On 10/12/2019 11:23, kbuild test robot wrote: > >>> include/linux/spinlock.h:378:9: sparse: sparse: context imbalance in 'walk_pte_range' - unexpected unlock > > I believe this is a false positive (although the trace here is useless). > This patch adds a conditional lock/unlock: > > pte = walk->no_vma ? pte_offset_map(pmd, addr) : > pte_offset_map_lock(walk->mm, pmd, addr, &ptl); > ... > if (!walk->no_vma) > spin_unlock(ptl); > pte_unmap(pte); > > I'm not sure how to match sparse happy about that. Is the only option to > have two versions of the walk_pte_range() function? One which takes the > lock and one which doesn't. Yes. -- Luc
> On Dec 11, 2019, at 10:54 AM, Steven Price <Steven.Price@arm.com> wrote: > > I believe this is a false positive (although the trace here is useless). > This patch adds a conditional lock/unlock: > > pte = walk->no_vma ? pte_offset_map(pmd, addr) : > pte_offset_map_lock(walk->mm, pmd, addr, &ptl); > ... > if (!walk->no_vma) > spin_unlock(ptl); > pte_unmap(pte); > > I'm not sure how to match sparse happy about that. Is the only option to > have two versions of the walk_pte_range() function? One which takes the > lock and one which doesn't. Or just ignore the sparse false positive without complicating the code further.
diff --git a/mm/pagewalk.c b/mm/pagewalk.c index efa464cf079b..1b9a3ba24c51 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -10,9 +10,10 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, pte_t *pte; int err = 0; const struct mm_walk_ops *ops = walk->ops; - spinlock_t *ptl; + spinlock_t *uninitialized_var(ptl); - pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl); + pte = walk->no_vma ? pte_offset_map(pmd, addr) : + pte_offset_map_lock(walk->mm, pmd, addr, &ptl); for (;;) { err = ops->pte_entry(pte, addr, addr + PAGE_SIZE, walk); if (err) @@ -23,7 +24,9 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, pte++; } - pte_unmap_unlock(pte, ptl); + if (!walk->no_vma) + spin_unlock(ptl); + pte_unmap(pte); return err; } @@ -383,6 +386,12 @@ int walk_page_range(struct mm_struct *mm, unsigned long start, return err; } +/* + * Similar to walk_page_range() but can walk any page tables even if they are + * not backed by VMAs. Because 'unusual' entries may be walked this function + * will also not lock the PTEs for the pte_entry() callback. This is useful for + * walking the kernel pages tables or page tables for firmware. + */ int walk_page_range_novma(struct mm_struct *mm, unsigned long start, unsigned long end, const struct mm_walk_ops *ops, void *private)
walk_page_range_novma() can be used to walk page tables or the kernel or for firmware. These page tables may contain entries that are not backed by a struct page and so it isn't (in general) possible to take the PTE lock for the pte_entry() callback. So update walk_pte_range() to only take the lock when no_vma==false and add a comment explaining the difference to walk_page_range_novma(). Signed-off-by: Steven Price <steven.price@arm.com> --- mm/pagewalk.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)