[PATCH 1/2] erofs-utils: lib: replace bool locked with erofs_mutex_t for MT safety

[Ajay]

Hi, This is my first time submitting patches via git send-email to a
mailing list, so I apologize if there are any formatting issues or
mistakes in the submission process. Any feedback or suggestions for
improvement are appreciated.
Thanks, Ajay Rajera.

On Thu, 19 Mar 2026 at 19:09, Ajay Rajera <newajay.11r at gmail.com> wrote:
>
> Replace the bool locked field in erofs_diskbufstrm with erofs_mutex_t lock to provide proper mutual exclusion for multi-threaded disk buffer operations. This addresses the TODO comment 'need a real lock for MT' by using the erofs mutex API (erofs_mutex_lock/erofs_mutex_unlock/erofs_mutex_init) instead of a simple boolean flag that provided no actual synchronization.
>
> Signed-off-by: Ajay Rajera <newajay.11r at gmail.com>
> ---
>  lib/diskbuf.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/lib/diskbuf.c b/lib/diskbuf.c
> index 0bf42da..4218df8 100644
> --- a/lib/diskbuf.c
> +++ b/lib/diskbuf.c
> @@ -3,6 +3,7 @@
>  #include "erofs/internal.h"
>  #include "erofs/print.h"
>  #include <stdio.h>
> +#include "erofs/lock.h"
>  #include <errno.h>
>  #include <sys/stat.h>
>  #include <unistd.h>
> @@ -14,7 +15,7 @@ static struct erofs_diskbufstrm {
>         u64 tailoffset, devpos;
>         int fd;
>         unsigned int alignsize;
> -       bool locked;
> +       erofs_mutex_t lock;
>  } *dbufstrm;
>
>  int erofs_diskbuf_getfd(struct erofs_diskbuf *db, u64 *fpos)
> @@ -34,6 +35,7 @@ int erofs_diskbuf_reserve(struct erofs_diskbuf *db, int sid, u64 *off)
>  {
>         struct erofs_diskbufstrm *strm = dbufstrm + sid;
>
> +       erofs_mutex_lock(&strm->lock);
>         if (strm->tailoffset & (strm->alignsize - 1)) {
>                 strm->tailoffset = round_up(strm->tailoffset, strm->alignsize);
>         }
> @@ -42,7 +44,6 @@ int erofs_diskbuf_reserve(struct erofs_diskbuf *db, int sid, u64 *off)
>                 *off = db->offset + strm->devpos;
>         db->sp = strm;
>         (void)erofs_atomic_inc_return(&strm->count);
> -       strm->locked = true;    /* TODO: need a real lock for MT */
>         return strm->fd;
>  }
>
> @@ -51,9 +52,9 @@ void erofs_diskbuf_commit(struct erofs_diskbuf *db, u64 len)
>         struct erofs_diskbufstrm *strm = db->sp;
>
>         DBG_BUGON(!strm);
> -       DBG_BUGON(!strm->locked);
>         DBG_BUGON(strm->tailoffset != db->offset);
>         strm->tailoffset += len;
> +       erofs_mutex_unlock(&strm->lock);
>  }
>
>  void erofs_diskbuf_close(struct erofs_diskbuf *db)
> @@ -115,6 +116,7 @@ int erofs_diskbuf_init(unsigned int nstrms)
>  setupone:
>                 strm->tailoffset = 0;
>                 erofs_atomic_set(&strm->count, 1);
> +               erofs_mutex_init(&strm->lock);
>                 if (fstat(strm->fd, &st))
>                         return -errno;
>                 strm->alignsize = max_t(u32, st.st_blksize, getpagesize());
> --
> 2.51.0.windows.1
>