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criu: fix log_keep_err signal deadlock

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When using pr_err in signal handler, locking is used
in an unsafe manner. If another signal happens while holding the
lock, deadlock can happen.

To fix this, we can introduce mutex_trylock similar to
pthread_mutex_trylock that returns immediately. Due to the fact
that lock is used only for writing first_err, this change garantees
that deadlock cannot happen.

Fixes: #358

Signed-off-by: Ivan Pravdin <ipravdin.official@gmail.com>
This commit is contained in:
Ivan Pravdin 2025-03-22 19:31:02 -04:00 committed by Andrei Vagin
parent 25f7185202
commit 2a428d20ce
2 changed files with 11 additions and 4 deletions
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3
criu/log.c
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@ -132,11 +132,12 @@ static void log_note_err(char *msg)
* anyway, so it doesn't make much sense to try hard * anyway, so it doesn't make much sense to try hard
* and optimize this out. * and optimize this out.
*/ */
mutex_lock(&first_err->l); if (mutex_trylock(&first_err->l)) {
if (first_err->s[0] == '\0') if (first_err->s[0] == '\0')
__strlcpy(first_err->s, msg, sizeof(first_err->s)); __strlcpy(first_err->s, msg, sizeof(first_err->s));
mutex_unlock(&first_err->l); mutex_unlock(&first_err->l);
} }
}
} }
char *log_first_err(void) char *log_first_err(void)

6
include/common/lock.h
View File

@ -2,6 +2,7 @@
#define __CR_COMMON_LOCK_H__ #define __CR_COMMON_LOCK_H__
#include <stdint.h> #include <stdint.h>
#include <stdbool.h>
#include <linux/futex.h> #include <linux/futex.h>
#include <sys/time.h> #include <sys/time.h>
#include <limits.h> #include <limits.h>
@ -162,6 +163,11 @@ static inline void mutex_lock(mutex_t *m)
} }
} }
static inline bool mutex_trylock(mutex_t *m)
{
return atomic_inc_return(&m->raw) == 1;
}
static inline void mutex_unlock(mutex_t *m) static inline void mutex_unlock(mutex_t *m)
{ {
uint32_t c = 0; uint32_t c = 0;