On Thu, Aug 01, 2019 at 06:50:57PM +0000, Luis Chamberlain wrote: > On Thu, Aug 01, 2019 at 07:06:35PM +0900, Tetsuo Handa wrote: > > When the system is close-to-OOM, fsync() may fail due to -ENOMEM because > > xfs_log_reserve() is using KM_MAYFAIL. It is a bad thing to fail writeback > > operation due to user-triggerable OOM condition. Since we are not using > > KM_MAYFAIL at xfs_trans_alloc() before calling xfs_log_reserve(), let's > > use the same flags at xfs_log_reserve(). > > > > oom-torture: page allocation failure: order:0, mode:0x46c40(GFP_NOFS|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_COMP), nodemask=(null) > > CPU: 7 PID: 1662 Comm: oom-torture Kdump: loaded Not tainted 5.3.0-rc2+ #925 > > Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 > > Call Trace: > > dump_stack+0x67/0x95 > > warn_alloc+0xa9/0x140 > > __alloc_pages_slowpath+0x9a8/0xbce > > __alloc_pages_nodemask+0x372/0x3b0 > > alloc_slab_page+0x3a/0x8d0 > > new_slab+0x330/0x420 > > ___slab_alloc.constprop.94+0x879/0xb00 > > __slab_alloc.isra.89.constprop.93+0x43/0x6f > > kmem_cache_alloc+0x331/0x390 > > kmem_zone_alloc+0x9f/0x110 [xfs] > > kmem_zone_alloc+0x9f/0x110 [xfs] > > xlog_ticket_alloc+0x33/0xd0 [xfs] > > xfs_log_reserve+0xb4/0x410 [xfs] > > xfs_trans_reserve+0x1d1/0x2b0 [xfs] > > xfs_trans_alloc+0xc9/0x250 [xfs] > > xfs_setfilesize_trans_alloc.isra.27+0x44/0xc0 [xfs] > > xfs_submit_ioend.isra.28+0xa5/0x180 [xfs] > > xfs_vm_writepages+0x76/0xa0 [xfs] > > do_writepages+0x17/0x80 > > __filemap_fdatawrite_range+0xc1/0xf0 > > file_write_and_wait_range+0x53/0xa0 > > xfs_file_fsync+0x87/0x290 [xfs] > > vfs_fsync_range+0x37/0x80 > > do_fsync+0x38/0x60 > > __x64_sys_fsync+0xf/0x20 > > do_syscall_64+0x4a/0x1c0 > > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > > > Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > > That's quite an opaque commit log for what started off as a severe email > thread of potential leak of information. As such, can you expand on this > commit log considerably to explain the situation a bit better? I'm pretty sure this didn't solve the underlying stale data exposure problem, which might be why you think this is "opaque". It fixes a bug that causes data writeback failure (which was the exposure vector this time) but I think the ultimate fix for the exposure problem are the two patches I linked to quite a ways back in this discussion.... --D https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?id=bd012b434a56d9fac3cbc33062b8e2cd6e1ad0a0 https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?id=adcf7c0c87191fd3616813c8ce9790f89a9a8eba > Your > initial thread here provided much clearer evidence of the issue. As-is > this commit log tells the reader *nothing* about the potential harm in > not applying this patch. > > You had mentioned you identified this issue present on at least > 4.18 till 5.3-rc1. So, I'm at least inclined to consider this for > stable for at least v4.19. > > However, what about older kernels? Now that you have identified > a fix, were the flag changed in prior commits, is it a regression > that perhaps added KM_MAYFAIL at some point? > > Luis
