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Wsn+zervsmZv9n1DqjLUSRfv+CoZzbqEtcQHcmE4GQaDSU0XoSSbic6NOilSRIza8FAbUnQ8SfgMl+CxFxRowtM49bRCNUApFSjFI64NdRY4IrxQPFDzmdP0dE8kRn/1nHSBxtCQZgn2FJASWMcPhZH9/swI4eDQLiDO0fw1zaK+3CJugaCbndWfnUjUatfrGVy5KA5rqXWjg+rRUawnYw0D2sprdoi2eYEgmy0rpj8KK+VBgK80BiBQBlcXXOzRtryGsHFkeVG1clbyZhpNtwE66z+2TbVdEUKAYOPMm+CBBwp4YLAV/dQ8NeNELtQcnTlYhLV5BrtXXuKIC4Tkhl27BhDeyzsyiEP9GXdxzvt1ZIjhHxEA8xLMlrw5bEhQH/qeyb1tXQZAc9adSx7zOMWqND8sEfHcpFyvkfb1i5cXaZUP04KIMvTXsfLLM7x0UB8jjau74k2zIkFGeCSvC49FUrDYaTKL7RKFl X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/19/24 13:48, Pavel Tikhomirov wrote: > Hello, > > I see that in kernel code we have couple of places where kvmalloc is > used with GFP_NOFS flag: > > git grep kvmalloc.*NOFS > fs/bcachefs/journal_io.c:       new_buf = kvmalloc(new_size, GFP_NOFS| > __GFP_NOWARN); > fs/ext4/xattr.c:                buffer = kvmalloc(value_size, GFP_NOFS); > fs/f2fs/compress.c:     cc->private = f2fs_kvmalloc(F2FS_I_SB(cc- > >inode), size, GFP_NOFS); > net/ceph/osdmap.c:      state = kvmalloc(array_size(max, > sizeof(*state)), GFP_NOFS); > net/ceph/osdmap.c:      weight = kvmalloc(array_size(max, > sizeof(*weight)), GFP_NOFS); > net/ceph/osdmap.c:      addr = kvmalloc(array_size(max, sizeof(*addr)), > GFP_NOFS); > > and with GFP_NOIO flag too: > > git grep kvmalloc.*NOIO > drivers/md/dm-integrity.c:      recalc_tags = kvmalloc(recalc_tags_size, > GFP_NOIO); > drivers/md/dm-ioctl.c:  dmi = kvmalloc(param_kernel->data_size, GFP_NOIO > | __GFP_HIGH); > net/ceph/messenger_v2.c:        buf = kvmalloc(len, GFP_NOIO); > net/ceph/osdmap.c:      work = kvmalloc(work_size, GFP_NOIO); > > And AFAIU documentation https://docs.kernel.org/core-api/gfp_mask-from- > fs-io.html#what-about-vmalloc-gfp-nofs vmalloc allocation with GFP_NOFS > may end up doing "GFP_KERNEL allocations deep inside the allocator", > which can potentially lead to deadlock in IO/FS code paths. > > Does it mean that we should rework all those paths to > memalloc_noio_save / memalloc_noio_restore variant? Or is it already > safe to use kvmalloc(GFP_NOIO) in modern kernel? > > Or maybe I misunderstand something, sorry in advance if that's the case. > Now when I've already sent a question I seemingly found the answer: In commit 451769ebb7e79 ("mm/vmalloc: alloc GFP_NO{FS,IO} for vmalloc") we add implicit memalloc_noXX_save/memalloc_noXX_restore at this code path: +->kvmalloc +-> ... +-> __kvmalloc_node_noprof +-> __vmalloc_node_range_noprof +-> __vmalloc_area_node So kvmalloc should be safe now with GFP_NOIO. Should we correct the documentation? -- Best regards, Tikhomirov Pavel Senior Software Developer, Virtuozzo.