On Thu, Dec 26, 2019 at 04:10:08PM +0900, Naoto Kobayashi wrote: > Although __vmalloc() doesn't support GFP_NOFS[1], > ext4_kvmalloc/kvzalloc caller may be under GFP_NOFS context > (e.g. fs/ext4/resize.c::add_new_gdb). In such cases, the memory > reclaim can re-entr the filesystem and potentially deadlock. > > To prevent the memory relcaim re-entring the filesystem, > use memalloc_nofs_save/restore that gets __vmalloc() to drop > __GFP_FS flag. > > [1] linux-tree/Documentation/core-api/gfp-mask-fs-io.rst > > Signed-off-by: Naoto Kobayashi <naoto.kobayashi4c@xxxxxxxxx> Good catch! However, we're not actually using ext4_kvzalloc() anywhere, at least not any more. And also, all the users of ext4_kvmalloc() are using GFP_NOFS (otherwise, they would have been converted over to use the generic kvmalloc() helper function). So... a cleaner fix would be to (a) delete ext4_kvmazalloc(), (b) rename ext4_kvmalloc() to ext4_kvmalloc_nofs(), and drop its flags argument, and then the calls memalloc_nfs_save/restore() to ext4_kvmalloc_nofs() --- and so we won't need the if (!(flags & __GFP_FS)) test. Could you make those changes and resend the patch? Thanks, - Ted
