[lkml]   [2021]   [Jul]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v2 1/2] tracing: Simplify & fix saved_tgids logic
On Thu, Jul 1, 2021 at 1:24 PM Paul Burton <> wrote:
> The tgid_map array records a mapping from pid to tgid, where the index
> of an entry within the array is the pid & the value stored at that index
> is the tgid.
> The saved_tgids_next() function iterates over pointers into the tgid_map
> array & dereferences the pointers which results in the tgid, but then it
> passes that dereferenced value to trace_find_tgid() which treats it as a
> pid & does a further lookup within the tgid_map array. It seems likely
> that the intent here was to skip over entries in tgid_map for which the
> recorded tgid is zero, but instead we end up skipping over entries for
> which the thread group leader hasn't yet had its own tgid recorded in
> tgid_map.
> A minimal fix would be to remove the call to trace_find_tgid, turning:
> if (trace_find_tgid(*ptr))
> into:
> if (*ptr)
> ..but it seems like this logic can be much simpler if we simply let
> seq_read() iterate over the whole tgid_map array & filter out empty
> entries by returning SEQ_SKIP from saved_tgids_show(). Here we take that
> approach, removing the incorrect logic here entirely.
> Signed-off-by: Paul Burton <>
> Fixes: d914ba37d714 ("tracing: Add support for recording tgid of tasks")
> Cc: Steven Rostedt <>
> Cc: Ingo Molnar <>
> Cc: Joel Fernandes <>

Reviewed-by: Joel Fernandes (Google) <>

 \ /
  Last update: 2021-07-01 20:07    [W:0.565 / U:0.008 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site