On 04/10, Matthew Wilcox wrote: > On Tue, Apr 10, 2018 at 10:45:45PM +0900, Minchan Kim wrote: > > On Tue, Apr 10, 2018 at 05:53:51AM -0700, Matthew Wilcox wrote: > > > From: Matthew Wilcox <mawil...@microsoft.com> > > > > > > The page cache has used the mapping's GFP flags for allocating > > > radix tree nodes for a long time. It took care to always mask off the > > > __GFP_HIGHMEM flag, and masked off other flags in other paths, but the > > > __GFP_ZERO flag was still able to sneak through. The __GFP_DMA and > > > __GFP_DMA32 flags would also have been able to sneak through if they > > > were ever used. Fix them all by using GFP_RECLAIM_MASK at the innermost > > > location, and remove it from earlier in the callchain. > > > > > > Fixes: 19f99cee206c ("f2fs: add core inode operations") > > > > Why this patch fix 19f99cee206c instead of 449dd6984d0e? > > F2FS doesn't have any problem before introducing 449dd6984d0e? > > Well, there's the problem. This bug is the combination of three different > things: > > 1. The working set code relying on list_empty. > 2. The page cache not filtering out the bad flags. > 3. F2FS specifying a flag nobody had ever specified before. > > So what single patch does this patch fix? I don't think it really matters.
Hope there'd be someone who does care about patch description though, IMHO, this fixes the MM regression introduced by: 449dd6984d0e ("mm: keep page cache radix tree nodes in check") merged in v3.15, 2014. 19f99cee206c ("f2fs: add core inode operations) merged in v3.8, 2012, just revealed this out. In fact, I've never hit this bug in old kernels. >From the user viewpoint, may I suggest to describe what kind of symptom we're able to see due to this bug? Something like: [ 7858.792946] [<ffffff80086f4de0>] __list_del_entry+0x30/0xd0 [ 7858.792951] [<ffffff8008362018>] list_lru_del+0xac/0x1ac [ 7858.792957] [<ffffff800830f04c>] page_cache_tree_insert+0xd8/0x110 [ 7858.792962] [<ffffff8008310188>] __add_to_page_cache_locked+0xf8/0x4e0 [ 7858.792967] [<ffffff800830ff34>] add_to_page_cache_lru+0x50/0x1ac [ 7858.792972] [<ffffff800830fdd0>] pagecache_get_page+0x468/0x57c [ 7858.792979] [<ffffff80085d081c>] __get_node_page+0x84/0x764 [ 7858.792986] [<ffffff800859cd94>] f2fs_iget+0x264/0xdc8 [ 7858.792991] [<ffffff800859ee00>] f2fs_lookup+0x3b4/0x660 [ 7858.792998] [<ffffff80083d2540>] lookup_slow+0x1e4/0x348 [ 7858.793003] [<ffffff80083d0eb8>] walk_component+0x21c/0x320 [ 7858.793008] [<ffffff80083d0010>] path_lookupat+0x90/0x1bc [ 7858.793013] [<ffffff80083cfe6c>] filename_lookup+0x8c/0x1a0 [ 7858.793018] [<ffffff80083c52d0>] vfs_fstatat+0x84/0x10c [ 7858.793023] [<ffffff80083c5b00>] SyS_newfstatat+0x28/0x64 Thanks,