On Mon, Dec 22, 2014 at 01:05:13PM -0500, Sasha Levin wrote: > On 12/22/2014 01:01 PM, Kirill A. Shutemov wrote: > > On Mon, Dec 22, 2014 at 10:04:02AM -0500, Sasha Levin wrote: > >> > Hi all, > >> > > >> > While fuzzing with trinity inside a KVM tools guest running the latest -next > >> > kernel, I've stumbled on the following spew: > >> > > >> > [ 432.376425] BUG: unable to handle kernel NULL pointer dereference at 0000000000000038 > >> > [ 432.378876] IP: down_write (./arch/x86/include/asm/rwsem.h:105 ./arch/x86/include/asm/rwsem.h:121 kernel/locking/rwsem.c:71) > > Looks like vma->vm_file->mapping is NULL. Somebody freed ->vm_file from > > under us? > > > > I suspect Davidlohr's patchset on i_mmap_lock, but I cannot find any code > > path which could lead to the crash. > > I've reported a different issue which that patchset: https://lkml.org/lkml/2014/12/9/741 > > I guess it could be related? Maybe. Other thing: unmap_mapping_range() i_mmap_lock_read(mapping); unmap_mapping_range_tree() unmap_mapping_range_vma() zap_page_range_single() unmap_single_vma() untrack_pfn() vma->vm_flags &= ~VM_PAT; It seems we modify ->vm_flags without mmap_sem taken, means we can corrupt them. Sasha could you check if you hit untrack_pfn()? The problem probably was hidden by exclusive i_mmap_lock on unmap_mapping_range(), but it's not exclusive anymore afrer Dave's patchset. Konstantin, you've modified untrack_pfn() back in 2012 to change ->vm_flags. Any coments? For now, I would propose to revert the commit and probably re-introduce it after v3.19: >From 14392c69fcfeeda34eb9f75d983dad32698cdd5c Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Date: Mon, 22 Dec 2014 21:01:54 +0200 Subject: [PATCH] Revert "mm/memory.c: share the i_mmap_rwsem" This reverts commit c8475d144abb1e62958cc5ec281d2a9e161c1946. There are several[1][2] of bug reports which points to this commit as potential cause[3]. Let's revert it until we figure out what's going on. [1] https://lkml.org/lkml/2014/11/14/342 [2] https://lkml.org/lkml/2014/12/22/213 [3] https://lkml.org/lkml/2014/12/9/741 Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx> Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Cc: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> --- mm/memory.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 649e7d440bd7..ca920d1fd314 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2378,12 +2378,12 @@ void unmap_mapping_range(struct address_space *mapping, details.last_index = ULONG_MAX; - i_mmap_lock_read(mapping); + i_mmap_lock_write(mapping); if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap))) unmap_mapping_range_tree(&mapping->i_mmap, &details); if (unlikely(!list_empty(&mapping->i_mmap_nonlinear))) unmap_mapping_range_list(&mapping->i_mmap_nonlinear, &details); - i_mmap_unlock_read(mapping); + i_mmap_unlock_write(mapping); } EXPORT_SYMBOL(unmap_mapping_range); -- Kirill A. Shutemov -- 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>