Re: [PATCH AUTOSEL 5.0 011/262] tracing: kdb: Fix ftdump to not sleep

From: Douglas Anderson dianders@chromium.org

[ Upstream commit 31b265b3baaf55f209229888b7ffea523ddab366 ]

As reported back in 2016-11 [1], the "ftdump" kdb command triggers a BUG for "sleeping function called from invalid context".

kdb's "ftdump" command wants to call ring_buffer_read_prepare() in atomic context. A very simple solution for this is to add allocation flags to ring_buffer_read_prepare() so kdb can call it without triggering the allocation error. This patch does that.

I see solution is simple, but now we have a loop with GFP_ATOMIC allocations inside. How many "tracing spus" is this expected to loop over? Will not it exhaust atomically available pages and reliably fail in common configurations? Pavel