On Tue, 20 May 2025 16:19:26 +0200 Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > On 05/20, Masami Hiramatsu wrote: > > > > On Thu, 15 May 2025 14:10:58 +0200 > > Jiri Olsa <jolsa@xxxxxxxxxx> wrote: > > > > > Currently unapply_uprobe takes mmap_read_lock, but it might call > > > remove_breakpoint which eventually changes user pages. > > > > > > Current code writes either breakpoint or original instruction, so > > > it can probably go away with that, but with the upcoming change that > > > writes multiple instructions on the probed address we need to ensure > > > that any update to mm's pages is exclusive. > > > > > > > So, this is a bugfix, right? > > No, mmap_read_lock() is fine. > > To remind, this was already discussed with you, see > [PATCH 02/12] uprobes: grab write mmap lock in unapply_uprobe() > https://lore.kernel.org/all/20240625002144.3485799-3-andrii@xxxxxxxxxx/ > > And you even reviewed this patch > [PATCH 1/2] uprobes: document the usage of mm->mmap_lock > https://lore.kernel.org/all/20240710140045.GA1084@xxxxxxxxxx/ > > But, as the changelog explains, this patch is needed for the upcoming changes. Oops, OK. So current code is good with either mmap_read_lock() or mmap_write_lock(). But the patch description is a bit confusing. If the point is an atomic (byte?) update or not, it should describe it. Thank you, > > -------------------------------------------------------------------------- > Just in case... I'll try to read this series tomorrow, but at first glance > this version addresses all my concerns. > > Oleg. > -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
