Messages in this thread | | | Subject | Re: [PATCH 01/12] uprobes: split THPs before trying replace them | From | Rik van Riel <> | Date | Wed, 25 Jan 2017 12:44:29 -0500 |
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On Wed, 2017-01-25 at 08:55 -0800, Srikar Dronamraju wrote: > > > > > > > > > > > > > > > > For THPs page_check_address() always fails. It's better to > > > > split them > > > > first before trying to replace. > > > So what does this mean. uprobes simply fails to work when trying > > > to > > > place a probe into a THP memory region? > > Looks like we can end up with endless retry loop in > > uprobe_write_opcode(). > > > > > > > > How come nobody noticed (and reported) this when using the > > > feature? > > I guess it's not often used for anon memory. > > > The first time the breakpoint is hit on a page, it replaces the text > page with anon page. Now lets assume we insert breakpoints in all > the > pages in a range. Here each page is individually replaced by a non > THP > anonpage. (since we dont have bulk breakpoint insertion support, > breakpoint insertion happens one at a time). Now the only interesting > case may be when each of these replaced pages happen to be physically > contiguous so that THP kicks in to replace all of these pages with > one > THP page. Can happen in practice? > > Are there any other cases that I have missed?
A JIT compiler placing executable code in anonymous memory before executing it, and a debugger trying to insert a uprobe in one of those areas?
Not common, but I suppose it could be done.
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