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? 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
