On 2019/12/26 23:39, Theodore Y. Ts'o wrote: > 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 > Thank you for the review! I made the changes you suggested and resent the patch. [PATCH v2 0/3] ext4: Prevent memory reclaim from re-entering the filesystem and deadlocking https://marc.info/?l=linux-ext4&m=157743393000807&w=2 Would you review the patch? Thanks, - Naoto
