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tuxtxt: fix race condition in tuxtxt_clear_cache()

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tuxtxt_cache_lock does not prevent from calling tuxtxt_clear_cache
while the cache thread is in the middle of inserting pages, thus
leading to a hard-to-reproduce crash when trying to start up tuxtxt.
The simplest fix is to use an additional "big hammer" lock arond
the whole critical area. Since tuxtxt_clear_cache is only called
very seldom, there should be no lock contention problem.
This commit is contained in:
Stefan Seyfried
2012-07-15 13:19:44 +02:00
parent 56b6f274c9
commit 9af56e1852
1 changed files with 15 additions and 1 deletions
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16
lib/libtuxtxt/tuxtxt_common.h
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@@ -1,4 +1,6 @@
/* tuxtxt_common.h
* for license info see the other tuxtxt files
*/
#include <sys/ioctl.h>
#include <fcntl.h>
#include <pthread.h>
@@ -15,6 +17,7 @@
tuxtxt_cache_struct tuxtxt_cache;
static pthread_mutex_t tuxtxt_cache_lock = PTHREAD_MUTEX_INITIALIZER;
static pthread_mutex_t tuxtxt_cache_biglock = PTHREAD_MUTEX_INITIALIZER;
int tuxtxt_get_zipsize(int p,int sp)
{
tstCachedPage* pg = tuxtxt_cache.astCachetable[p][sp];
@@ -350,6 +353,7 @@ int tuxtxt_GetSubPage(int page, int subpage, int offset)
void tuxtxt_clear_cache(void)
{
pthread_mutex_lock(&tuxtxt_cache_biglock);
pthread_mutex_lock(&tuxtxt_cache_lock);
int clear_page, clear_subpage, d26;
tuxtxt_cache.maxadippg = -1;
@@ -413,6 +417,7 @@ void tuxtxt_clear_cache(void)
printf("TuxTxt cache cleared\n");
#endif
pthread_mutex_unlock(&tuxtxt_cache_lock);
pthread_mutex_unlock(&tuxtxt_cache_biglock);
}
/******************************************************************************
* init_demuxer *
@@ -540,6 +545,7 @@ void tuxtxt_allocate_cache(int magazine)
// Lock here as we have a possible race here with
// tuxtxt_clear_cache(). We should not be allocating and
// freeing at the same time.
// *** this is probably worked around by tuxtxt_cacehe_biglock now *** --seife
pthread_mutex_lock(&tuxtxt_cache_lock);
/* check cachetable and allocate memory if needed */
@@ -612,6 +618,13 @@ void *tuxtxt_CacheThread(void * /*arg*/)
continue;
}
/* this "big hammer lock" is a hack: it avoids a crash if
* tuxtxt_clear_cache() is called while the cache thread is in the
* middle of the following loop, leading to tuxtxt_cache.current_page[]
* etc. being set to -1 and tuxtxt_cache.astCachetable[] etc. being set
* to NULL
* it probably also avoids the possible race in tuxtxt_allocate_cache() */
pthread_mutex_lock(&tuxtxt_cache_biglock);
/* analyze it */
for (line = 0; line < readcnt/0x2e /*4*/; line++)
{
@@ -1053,6 +1066,7 @@ void *tuxtxt_CacheThread(void * /*arg*/)
printf("line %d row %X %X, continue\n", line, vtx_rowbyte[0], vtx_rowbyte[1]);
#endif
}
pthread_mutex_unlock(&tuxtxt_cache_biglock);
}
pthread_exit(NULL);