Hello Laurent, hello Peter,
I see the Maximum number of active timers ist still 32. I hope it is not
too late, but for my application this is not enough. Could this define be
bigger i.e. 32*4?
Thanks for your support! I really appreciate it!
Jon
Laurent Vivier <laur...@vivier.eu> igorleak hau idatzi zuen (2022 ira. 28,
az. 10:15):
> From: Peter Maydell <peter.mayd...@linaro.org>
>
> For handling guest POSIX timers, we currently use an array
> g_posix_timers[], whose entries are a host timer_t value, or 0 for
> "this slot is unused". When the guest calls the timer_create syscall
> we look through the array for a slot containing 0, and use that for
> the new timer.
>
> This scheme assumes that host timer_t values can never be zero. This
> is unfortunately not a valid assumption -- for some host libc
> versions, timer_t values are simply indexes starting at 0. When
> using this kind of host libc, the effect is that the first and second
> timers end up sharing a slot, and so when the guest tries to operate
> on the first timer it changes the second timer instead.
>
> Rework the timer allocation code, so that:
> * the 'slot in use' indication uses a separate array from the
> host timer_t array
> * we grab the free slot atomically, to avoid races when multiple
> threads call timer_create simultaneously
> * releasing an allocated slot is abstracted out into a new
> free_host_timer_slot() function called in the correct places
>
> This fixes:
> * problems on hosts where timer_t 0 is valid
> * the FIXME in next_free_host_timer() about locking
> * bugs in the error paths in timer_create where we forgot to release
> the slot we grabbed, or forgot to free the host timer
>
> Reported-by: Jon Alduan <jon.ald...@gmail.com>
> Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
> Message-Id: <20220725110035.1273441-1-peter.mayd...@linaro.org>
> Signed-off-by: Laurent Vivier <laur...@vivier.eu>
> ---
> linux-user/syscall.c | 24 ++++++++++++++++--------
> 1 file changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 54b29f3b406a..e0e0f058121f 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -525,20 +525,25 @@ _syscall4(int, sys_prlimit64, pid_t, pid, int,
> resource,
>
> #if defined(TARGET_NR_timer_create)
> /* Maximum of 32 active POSIX timers allowed at any one time. */
> -static timer_t g_posix_timers[32] = { 0, } ;
> +#define GUEST_TIMER_MAX 32
> +static timer_t g_posix_timers[GUEST_TIMER_MAX];
> +static int g_posix_timer_allocated[GUEST_TIMER_MAX];
>
> static inline int next_free_host_timer(void)
> {
> - int k ;
> - /* FIXME: Does finding the next free slot require a lock? */
> - for (k = 0; k < ARRAY_SIZE(g_posix_timers); k++) {
> - if (g_posix_timers[k] == 0) {
> - g_posix_timers[k] = (timer_t) 1;
> + int k;
> + for (k = 0; k < ARRAY_SIZE(g_posix_timer_allocated); k++) {
> + if (qatomic_xchg(g_posix_timer_allocated + k, 1) == 0) {
> return k;
> }
> }
> return -1;
> }
> +
> +static inline void free_host_timer_slot(int id)
> +{
> + qatomic_store_release(g_posix_timer_allocated + id, 0);
> +}
> #endif
>
> static inline int host_to_target_errno(int host_errno)
> @@ -12896,15 +12901,18 @@ static abi_long do_syscall1(CPUArchState
> *cpu_env, int num, abi_long arg1,
> phost_sevp = &host_sevp;
> ret = target_to_host_sigevent(phost_sevp, arg2);
> if (ret != 0) {
> + free_host_timer_slot(timer_index);
> return ret;
> }
> }
>
> ret = get_errno(timer_create(clkid, phost_sevp, phtimer));
> if (ret) {
> - phtimer = NULL;
> + free_host_timer_slot(timer_index);
> } else {
> if (put_user(TIMER_MAGIC | timer_index, arg3,
> target_timer_t)) {
> + timer_delete(*phtimer);
> + free_host_timer_slot(timer_index);
> return -TARGET_EFAULT;
> }
> }
> @@ -13040,7 +13048,7 @@ static abi_long do_syscall1(CPUArchState *cpu_env,
> int num, abi_long arg1,
> } else {
> timer_t htimer = g_posix_timers[timerid];
> ret = get_errno(timer_delete(htimer));
> - g_posix_timers[timerid] = 0;
> + free_host_timer_slot(timerid);
> }
> return ret;
> }
> --
> 2.37.3
>
>
