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

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Commit 1af615683e 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>
This commit is contained in:
Andreas Rheinhardt 2020-11-18 21:38:45 +01:00
parent 5c45f7e156
commit b9c1ab8907
4 changed files with 23 additions and 19 deletions
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24
libavcodec/fft_init_table.c
View File

@ -51,6 +51,8 @@
* @file
* definitions and initialization of LUT table for FFT
*/
#include "libavutil/thread.h"
#include "libavcodec/fft_table.h"
const int32_t ff_w_tab_sr[MAX_FFT_SIZE/(4*16)] = {
@ -314,15 +316,29 @@ const int32_t ff_w_tab_sr[MAX_FFT_SIZE/(4*16)] = {
uint16_t ff_fft_offsets_lut[21845];
void ff_fft_lut_init(uint16_t *table, int off, int size, int *index)
static void fft_lut_init(uint16_t *table, int off, int size, int *index)
{
if (size < 16) {
table[*index] = off >> 2;
(*index)++;
}
else {
ff_fft_lut_init(table, off, size>>1, index);
ff_fft_lut_init(table, off+(size>>1), size>>2, index);
ff_fft_lut_init(table, off+3*(size>>2), size>>2, index);
fft_lut_init(table, off, size >> 1, index);
fft_lut_init(table, off + (size >> 1), size >> 2, index);
fft_lut_init(table, off + 3 * (size >> 2), size >> 2, index);
}
}
static void fft_lut_init_start(void)
{
int n = 0;
fft_lut_init(ff_fft_offsets_lut, 0, 1 << 17, &n);
}
void ff_fft_lut_init(void)
{
static AVOnce init_once = AV_ONCE_INIT;
ff_thread_once(&init_once, fft_lut_init_start);
}

2
libavcodec/fft_table.h
View File

@ -61,6 +61,6 @@
extern const int32_t ff_w_tab_sr[];
extern uint16_t ff_fft_offsets_lut[];
void ff_fft_lut_init(uint16_t *table, int off, int size, int *index);
void ff_fft_lut_init(void);
#endif /* AVCODEC_FFT_TABLE_H */

12
libavcodec/fft_template.c
View File

@ -35,13 +35,6 @@
#if FFT_FIXED_32
#include "fft_table.h"
static void av_cold fft_lut_init(void)
{
int n = 0;
ff_fft_lut_init(ff_fft_offsets_lut, 0, 1 << 17, &n);
}
#else /* FFT_FIXED_32 */
/* cos(2*pi*x/n) for 0<=x<=n/4, followed by its reverse */
@ -236,10 +229,7 @@ av_cold int ff_fft_init(FFTContext *s, int nbits, int inverse)
#endif
#if FFT_FIXED_32
{
static AVOnce control = AV_ONCE_INIT;
ff_thread_once(&control, fft_lut_init);
}
ff_fft_lut_init();
#else /* FFT_FIXED_32 */
#if FFT_FLOAT
if (ARCH_AARCH64) ff_fft_init_aarch64(s);

4
libavcodec/mips/fft_mips.c
View File

@ -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