Messages in this thread | | | Date | Fri, 16 May 2014 21:29:49 +0200 | From | Oleg Nesterov <> | Subject | Re: uprobes && shmem (Was: uprobes: Shift ->readpage check from __copy_insn() to uprobe_register()) |
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On 05/16, Hugh Dickins wrote: > > 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.
Thanks to Denys ;)
> > 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().
Even better, thanks,
> > 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.
Heh. I need to do git pull more often, I guess. Great.
> 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, thanks a lot!
Oleg.
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