Hi,
On Thu, Mar 28, 2019 at 3:13 AM Pavel Machek pavel@ucw.cz wrote:
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
Each one of these allocations is ~32 bytes and you do one per CPU. Even with systems with a lot of CPUs that's not going to be tons. ...and you only do it with GFP_ATOMIC when you're actively dropped into kdb and debugging. It seems like going for simplicity is the right call here, but of course if Steven or Daniel say that it has to be done a different way then they're the true authorities.
-Doug