On Wed, Sep 12, 2012 at 02:32:39PM -0700, Andrew Morton wrote: > On Wed, 12 Sep 2012 10:43:51 +0900 > Minchan Kim <minchan@xxxxxxxxxx> wrote: > > > [1] reporeted that lowmem pages could be replaced by > > highmem pages during migration of CMA and fixed. > > > > Quote from [1]'s description > > " > > The filesystem layer expects pages in the block device's mapping to not > > be in highmem (the mapping's gfp mask is set in bdget()), but CMA can > > currently replace lowmem pages with highmem pages, leading to crashes in > > filesystem code such as the one below: > > > > Unable to handle kernel NULL pointer dereference at virtual address 00000400 > > pgd = c0c98000 > > [00000400] *pgd=00c91831, *pte=00000000, *ppte=00000000 > > Internal error: Oops: 817 [#1] PREEMPT SMP ARM > > CPU: 0 Not tainted (3.5.0-rc5+ #80) > > PC is at __memzero+0x24/0x80 > > ... > > Process fsstress (pid: 323, stack limit = 0xc0cbc2f0) > > Backtrace: > > [<c010e3f0>] (ext4_getblk+0x0/0x180) from [<c010e58c>] (ext4_bread+0x1c/0x98) > > [<c010e570>] (ext4_bread+0x0/0x98) from [<c0117944>] (ext4_mkdir+0x160/0x3bc) > > r4:c15337f0 > > [<c01177e4>] (ext4_mkdir+0x0/0x3bc) from [<c00c29e0>] (vfs_mkdir+0x8c/0x98) > > [<c00c2954>] (vfs_mkdir+0x0/0x98) from [<c00c2a60>] (sys_mkdirat+0x74/0xac) > > r6:00000000 r5:c152eb40 r4:000001ff r3:c14b43f0 > > [<c00c29ec>] (sys_mkdirat+0x0/0xac) from [<c00c2ab8>] (sys_mkdir+0x20/0x24) > > r6:beccdcf0 r5:00074000 r4:beccdbbc > > [<c00c2a98>] (sys_mkdir+0x0/0x24) from [<c000e3c0>] (ret_fast_syscall+0x0/0x30) > > " > > > > Memory-hotplug has same problem with CMA so [1]'s fix could be applied > > with memory-hotplug, too. > > > > Fix it by reusing. > > Do we think this issue should be fixed in 3.6? Earlier? I really wanted to Cced stable but didn't due to a below - It must fix a real bug that bothers people (not a, "This could be a problem..." type thing). We haven't ever seen at the report of memory-hotplug although it pops up in CMA. But I doubt fujitsu guys already saw it. > > > @@ -809,8 +802,12 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn) > > putback_lru_pages(&source); > > goto out; > > } > > - /* this function returns # of failed pages */ > > - ret = migrate_pages(&source, hotremove_migrate_alloc, 0, > > + > > + /* > > + * alloc_migrate_target should be improooooved!! > > Not a helpful comment! If you've identified some improvement then > please do provide all the details. I have an idea to improve it and hoping send patch soonish. I will handle it in my patch. Thanks Andrew. -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>