On Wed, Sep 12 2012, Minchan Kim 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. > > [1] 6a6dccba2, mm: cma: don't replace lowmem pages with highmem > > Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > Cc: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx> > Cc: Michal Nazarewicz <mina86@xxxxxxxxxx> Looks legit: Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx> I also like how both of the patches cumulatively have negative delta. :] > Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > Cc: Wen Congyang <wency@xxxxxxxxxxxxxx> > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> -- Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o ..o | Computer Science, Michał “mina86” Nazarewicz (o o) ooo +----<email/xmpp: mpn@xxxxxxxxxx>--------------ooO--(_)--Ooo--
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