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authorMartin Schwidefsky <schwidefsky@de.ibm.com>2018-10-15 11:09:16 +0200
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2018-11-02 08:31:55 +0100
commite12e4044aede97974f2222eb7f0ed726a5179a32 (patch)
treee3b45d8ffb6b65e34cba58ee7af157c6bd33755c /arch/s390/mm
parent6d212db11947ae5464e4717536ed9faf61c01e86 (diff)
downloadlinux-e12e4044aede97974f2222eb7f0ed726a5179a32.tar.bz2
s390/mm: fix mis-accounting of pgtable_bytes
In case a fork or a clone system fails in copy_process and the error handling does the mmput() at the bad_fork_cleanup_mm label, the following warning messages will appear on the console: BUG: non-zero pgtables_bytes on freeing mm: 16384 The reason for that is the tricks we play with mm_inc_nr_puds() and mm_inc_nr_pmds() in init_new_context(). A normal 64-bit process has 3 levels of page table, the p4d level and the pud level are folded. On process termination the free_pud_range() function in mm/memory.c will subtract 16KB from pgtable_bytes with a mm_dec_nr_puds() call, but there actually is not really a pud table. One issue with this is the fact that pgtable_bytes is usually off by a few kilobytes, but the more severe problem is that for a failed fork or clone the free_pgtables() function is not called. In this case there is no mm_dec_nr_puds() or mm_dec_nr_pmds() that go together with the mm_inc_nr_puds() and mm_inc_nr_pmds in init_new_context(). The pgtable_bytes will be off by 16384 or 32768 bytes and we get the BUG message. The message itself is purely cosmetic, but annoying. To fix this override the mm_pmd_folded, mm_pud_folded and mm_p4d_folded function to check for the true size of the address space. Reported-by: Li Wang <liwang@redhat.com> Tested-by: Li Wang <liwang@redhat.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch/s390/mm')
-rw-r--r--arch/s390/mm/pgalloc.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
index 76d89ee8b428..814f26520aa2 100644
--- a/arch/s390/mm/pgalloc.c
+++ b/arch/s390/mm/pgalloc.c
@@ -101,6 +101,7 @@ int crst_table_upgrade(struct mm_struct *mm, unsigned long end)
mm->context.asce_limit = _REGION1_SIZE;
mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
_ASCE_USER_BITS | _ASCE_TYPE_REGION2;
+ mm_inc_nr_puds(mm);
} else {
crst_table_init(table, _REGION1_ENTRY_EMPTY);
pgd_populate(mm, (pgd_t *) table, (p4d_t *) pgd);