avcodec/fft_template, fft_init_table: Make ff_fft_init() thread-safe

Commit 1af615683e4a1a858407afbaa2fd686842da7e49 put initializing
the ff_fft_offsets_lut (which is typically used if FFT_FIXED_32)
behind an ff_thread_once() to make ff_fft_init() thread-safe; yet
there is a second place where said table may be initialized which
is not guarded by this AVOnce: ff_fft_init_mips(). MIPS uses this LUT
even for ordinary floating point FFTs, so that ff_fft_init() is not
thread-safe (on MIPS) for both 32bit fixed-point as well as
floating-point FFTs; e.g. ff_mdct_init() inherits this flaw and
therefore initializing e.g. the AAC decoders is not thread-safe (on
MIPS) despite them having FF_CODEC_CAP_INIT_CLEANUP set.

This commit fixes this by moving the AVOnce to fft_init_table.c and
using it to guard all initializations of ff_fft_offsets_lut.

(It is not that bad in practice, because every entry of
ff_fft_offsets_lut is never read during initialization and is only once
ever written to (namely to its final value); but even these are
conflicting actions which are (by definition) data races and lead to
undefined behaviour.)

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

1 files changed, 1 insertions, 3 deletions

diff --git a/libavcodec/mips/fft_mips.c b/libavcodec/mips/fft_mips.c
index 69abdc8a08..a6656d9650 100644
--- a/libavcodec/mips/fft_mips.c
+++ b/libavcodec/mips/fft_mips.c
@@ -500,9 +500,7 @@ static void ff_imdct_calc_mips(FFTContext *s, FFTSample *output, const FFTSample
 
 av_cold void ff_fft_init_mips(FFTContext *s)
 {
-    int n=0;
-
-    ff_fft_lut_init(ff_fft_offsets_lut, 0, 1 << 17, &n);
+    ff_fft_lut_init();
     ff_init_ff_cos_tabs(17);
 
 #if HAVE_INLINE_ASM