Re: [PATCH v2] fuse: invalidate readdir cache on epoch bump

[Luis Henriques <luis@igalia.com>]

On Thu, May 14 2026, Jun Wu wrote:

> From: Jun Wu <quark@meta.com>
>
> FUSE_NOTIFY_INC_EPOCH invalidates dentries, but does not invalidate cached
> readdir results. A process with cwd inside a FUSE mount can therefore
> observe stale readdir(".") output after an epoch bump.
>
> Fix this by recording epoch in the readdir cache and checking it on reuse.
>
> Minimal reproducer:
>
> - mount a tiny FUSE fs with an empty root directory
> - on opendir, enable fi->cache_readdir and fi->keep_cache
> - chdir into the mount and call readdir(".") to populate readdir cache
> - make the FUSE server report one file in the root directory
> - send only FUSE_NOTIFY_INC_EPOCH
> - call readdir(".") again; before this change it stays stale, after this
>   change it sees the new file
>
> Fixes: 2396356a945b ("fuse: add more control over cache invalidation behaviour")
> Signed-off-by: Jun Wu <quark@meta.com>

Nice catch!  The fix looks good to me, so feel free to add my

Reviewed-by: Luis Henriques <luis@igalia.com>

Cheers,
-- 
Luís

> ---
> Changes in v2:
> - Addresses Joanne Koong's suggestions:
>   - Drop the FUSE_EPOCH_READDIR init flag.
>   - Add Fixes tag.
> - Rebase onto current mainline.
> ---
>  fs/fuse/dev.c     | 6 +++---
>  fs/fuse/fuse_i.h  | 3 +++
>  fs/fuse/readdir.c | 5 ++++-
>  3 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index 5dda7080f4a9..35e04b064f37 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -2038,9 +2038,9 @@ static int fuse_notify_resend(struct fuse_conn *fc)
>  }
>  
>  /*
> - * Increments the fuse connection epoch.  This will result of dentries from
> - * previous epochs to be invalidated.  Additionally, if inval_wq is set, a work
> - * queue is scheduled to trigger the invalidation.
> + * Increments the fuse connection epoch.  This will cause dentries and
> + * readdir caches from previous epochs to be invalidated.  Additionally,
> + * if inval_wq is set, a work queue is scheduled to trigger the invalidation.
>   */
>  static int fuse_notify_inc_epoch(struct fuse_conn *fc)
>  {
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index 17423d4e3cfa..aa8d6dfbbcc7 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -191,6 +191,9 @@ struct fuse_inode {
>  			/* iversion of directory when cache was started */
>  			u64 iversion;
>  
> +			/* epoch of fc when cache was started */
> +			int epoch;
> +
>  			/* protects above fields */
>  			spinlock_t lock;
>  		} rdc;
> diff --git a/fs/fuse/readdir.c b/fs/fuse/readdir.c
> index db5ae8ec1030..b18d971e2bb4 100644
> --- a/fs/fuse/readdir.c
> +++ b/fs/fuse/readdir.c
> @@ -442,6 +442,7 @@ static void fuse_rdc_reset(struct inode *inode)
>  	fi->rdc.version++;
>  	fi->rdc.size = 0;
>  	fi->rdc.pos = 0;
> +	fi->rdc.epoch = 0;
>  }
>  
>  #define UNCACHED 1
> @@ -483,6 +484,7 @@ static int fuse_readdir_cached(struct file *file, struct dir_context *ctx)
>  		if (!ctx->pos && !fi->rdc.size) {
>  			fi->rdc.mtime = inode_get_mtime(inode);
>  			fi->rdc.iversion = inode_query_iversion(inode);
> +			fi->rdc.epoch = atomic_read(&fc->epoch);
>  		}
>  		spin_unlock(&fi->rdc.lock);
>  		return UNCACHED;
> @@ -496,7 +498,8 @@ static int fuse_readdir_cached(struct file *file, struct dir_context *ctx)
>  		struct timespec64 mtime = inode_get_mtime(inode);
>  
>  		if (inode_peek_iversion(inode) != fi->rdc.iversion ||
> -		    !timespec64_equal(&fi->rdc.mtime, &mtime)) {
> +		    !timespec64_equal(&fi->rdc.mtime, &mtime) ||
> +		    fi->rdc.epoch != atomic_read(&fc->epoch)) {
>  			fuse_rdc_reset(inode);
>  			goto retry_locked;
>  		}
> -- 
> 2.54.0
>