| Message ID | alpine.LRH.2.02.1503181328450.17058@file01.intranet.prod.int.rdu2.redhat.com (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
On Wed, Mar 18, 2015 at 01:42:38PM -0400, Mikulas Patocka wrote: > > > On Wed, 18 Mar 2015, Kirill A. Shutemov wrote: > > > On Wed, Mar 18, 2015 at 12:25:11PM -0400, Mikulas Patocka wrote: > > > > > > > > > On Wed, 18 Mar 2015, Kirill A. Shutemov wrote: > > > > > > > On Wed, Mar 18, 2015 at 11:16:42AM -0400, Mikulas Patocka wrote: > > > > > Hi > > > > > > > > > > Here I'm sending a patch that fixes numerous "BUG: non-zero nr_pmds on > > > > > freeing mm: -1" errors on 64-bit PA-RISC kernel. > > > > > > > > > > I think the patch posted here > > > > > http://www.spinics.net/lists/linux-parisc/msg05981.html is incorrect, it > > > > > wouldn't work if the affected address range is freed and allocated > > > > > multiple times. > > > > > - 1. alloc pgd with built-in pmd, the count of pmds is 1 > > > > > - 2. free the range covered by the built-in pmd, the count of pmds > > > > > is 0, but the built-in pmd is still present > > > > > > > > Hm. Okay. I didn't realize you have special case in pmd_clear() for these > > > > pmds. > > > > > > > > What about adding mm_inc_nr_pmds() in pmd_clear() for PxD_FLAG_ATTACHED > > > > to compensate mm_dec_nr_pmds() in free_pmd_range()? > > > > > > pmd_clear clears one entry in the pmd, it wouldn't work. You need to add > > > it to pgd_clear. That clears the pointer to the pmd (and does nothing if > > > it is asked to clear the pointer to the preallocated pmd). But pgd_clear > > > doesn't receive the pointer to mm. > > > > I meant pmd_free(), not pmd_clear(). This should work fine. > > OK, here is the updated patch. > > > From: Mikulas Patocka <mpatocka@redhat.com> > > The patch dc6c9a35b66b520cf67e05d8ca60ebecad3b0479 that counts pmds > allocated for a process introduced a bug on 64-bit PA-RISC kernels. > > The PA-RISC architecture preallocates one pmd with each pgd. This > preallocated pmd can never be freed - pmd_free does nothing when it is > called with this pmd. When the kernel attempts to free this preallocated > pmd, it decreases the count of allocated pmds. The result is that the > counter underflows and this error is reported. > > This patch fixes the bug by artifically incrementing the counter in > pmd_free when the kernel tries to free the preallocated pmd. > > Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > --- > arch/parisc/include/asm/pgalloc.h | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > Index: linux-4.0-rc4/arch/parisc/include/asm/pgalloc.h > =================================================================== > --- linux-4.0-rc4.orig/arch/parisc/include/asm/pgalloc.h 2015-03-18 18:02:16.000000000 +0100 > +++ linux-4.0-rc4/arch/parisc/include/asm/pgalloc.h 2015-03-18 18:03:26.000000000 +0100 > @@ -74,8 +74,13 @@ static inline void pmd_free(struct mm_st > { > #ifdef CONFIG_64BIT > if(pmd_flag(*pmd) & PxD_FLAG_ATTACHED) > - /* This is the permanent pmd attached to the pgd; > - * cannot free it */ > + /* > + * This is the permanent pmd attached to the pgd; > + * cannot free it. > + * Increment the counter to compensate for the decrement > + * done by generic mm code. > + */ > + mm_inc_nr_pmds(mm); > return; > #endif > free_pages((unsigned long)pmd, PMD_ORDER); > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
Index: linux-4.0-rc4/arch/parisc/include/asm/pgalloc.h =================================================================== --- linux-4.0-rc4.orig/arch/parisc/include/asm/pgalloc.h 2015-03-18 18:02:16.000000000 +0100 +++ linux-4.0-rc4/arch/parisc/include/asm/pgalloc.h 2015-03-18 18:03:26.000000000 +0100 @@ -74,8 +74,13 @@ static inline void pmd_free(struct mm_st { #ifdef CONFIG_64BIT if(pmd_flag(*pmd) & PxD_FLAG_ATTACHED) - /* This is the permanent pmd attached to the pgd; - * cannot free it */ + /* + * This is the permanent pmd attached to the pgd; + * cannot free it. + * Increment the counter to compensate for the decrement + * done by generic mm code. + */ + mm_inc_nr_pmds(mm); return; #endif free_pages((unsigned long)pmd, PMD_ORDER);