On Wed, Oct 24, 2012 at 09:36:27PM -0700, Hugh Dickins wrote: > On Wed, 24 Oct 2012, Dave Jones wrote: > > > Machine under significant load (4gb memory used, swap usage fluctuating) > > triggered this... > > > > WARNING: at mm/shmem.c:1151 shmem_getpage_gfp+0xa5c/0xa70() > > Pid: 29795, comm: trinity-child4 Not tainted 3.7.0-rc2+ #49 > > Call Trace: > > [<ffffffff8107100f>] warn_slowpath_common+0x7f/0xc0 > > [<ffffffff8107106a>] warn_slowpath_null+0x1a/0x20 > > [<ffffffff811903fc>] shmem_getpage_gfp+0xa5c/0xa70 > > [<ffffffff8118fc3e>] ? shmem_getpage_gfp+0x29e/0xa70 > > [<ffffffff81190e4f>] shmem_fault+0x4f/0xa0 > > [<ffffffff8119f391>] __do_fault+0x71/0x5c0 > > [<ffffffff810e1ac6>] ? __lock_acquire+0x306/0x1ba0 > > [<ffffffff810b6ff9>] ? local_clock+0x89/0xa0 > > [<ffffffff811a2767>] handle_pte_fault+0x97/0xae0 > > [<ffffffff816d1069>] ? sub_preempt_count+0x79/0xd0 > > [<ffffffff8136d68e>] ? delay_tsc+0xae/0x120 > > [<ffffffff8136d578>] ? __const_udelay+0x28/0x30 > > [<ffffffff811a4a39>] handle_mm_fault+0x289/0x350 > > [<ffffffff816d091e>] __do_page_fault+0x18e/0x530 > > [<ffffffff810b6ff9>] ? local_clock+0x89/0xa0 > > [<ffffffff810b0e51>] ? get_parent_ip+0x11/0x50 > > [<ffffffff810b0e51>] ? get_parent_ip+0x11/0x50 > > [<ffffffff816d1069>] ? sub_preempt_count+0x79/0xd0 > > [<ffffffff8112d389>] ? rcu_user_exit+0xc9/0xf0 > > [<ffffffff816d0ceb>] do_page_fault+0x2b/0x50 > > [<ffffffff816cd3b8>] page_fault+0x28/0x30 > > [<ffffffff8136d259>] ? copy_user_enhanced_fast_string+0x9/0x20 > > [<ffffffff8121c181>] ? sys_futimesat+0x41/0xe0 > > [<ffffffff8102bf35>] ? syscall_trace_enter+0x25/0x2c0 > > [<ffffffff816d5625>] ? tracesys+0x7e/0xe6 > > [<ffffffff816d5688>] tracesys+0xe1/0xe6 > > > > > > > > 1148 error = shmem_add_to_page_cache(page, mapping, index, > > 1149 gfp, swp_to_radix_entry(swap)); > > 1150 /* We already confirmed swap, and make no allocation */ > > 1151 VM_BUG_ON(error); > > 1152 } > > That's very surprising. Easy enough to handle an error there, but > of course I made it a VM_BUG_ON because it violates my assumptions: > I rather need to understand how this can be, and I've no idea. Could it be concurrent truncation clearing out the entry between shmem_confirm_swap() and shmem_add_to_page_cache()? I don't see anything preventing that. The empty slot would not match the expected swap entry this call passes in and the returned error would be -ENOENT. -- 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>