Messages in this thread | | | Date | Fri, 16 May 2014 11:49:54 -0700 (PDT) | From | Hugh Dickins <> | Subject | Re: uprobes && shmem (Was: uprobes: Shift ->readpage check from __copy_insn() to uprobe_register()) |
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On Fri, 16 May 2014, Oleg Nesterov wrote: > On 05/16, Oleg Nesterov wrote: > > > > copy_insn() fails with -EIO if ->readpage == NULL > > In particular, this means that we can not probe the binaries on tmpfs. > This is pity.
Yes, that is a pity: thanks for noticing.
> > It seems that the potential fix is trivial, copy_insn() could use > shmem_getpage_gfp(). But, is there any way to figure out that this
shmem_getpage_gfp() itself is static: please use shmem_read_mapping_page(mapping, pgoff): inline in linux/shmem_fs.h, calls shmem_read_mapping_page_gfp() in mm/shmem.c (a very few places need to override gfp_mask too: you do not), calls shmem_getpage_gfp().
> inode/mapping/aops/whatever is actually shmem? > > I am looking at shmem_get_inode() and I see nothing which could help, > and shmem_aops/etc are all static.
On 3.15 and later, you're in luck: Hannes added bool shmem_mapping(mapping) in his 0cd6144aadd2 "mm + fs: prepare for non-page entries in page cache radix trees"; and I just checked, it builds for "tiny" !CONFIG_SHMEM too.
If you're backporting to an earlier kernel, it would probably be best to add in a very small patch, extracting just shmem_mapping() and its linux/mm.h declarations from 0cd6144aadd2.
I notice shmem_mapping() checks backing_dev_info, whereas shmem_get_mapping_page_gfp() checks a_ops: no problem in that. But it reminds me that you should test uprobe on SysV SHM when you're done: again I think no problem, but there's an incestuous relationship between shm and shmem that can catch us out when adding such checks.
Hugh
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