Message ID | 20171025093809.GB32700@veci.piliscsaba.szeredi.hu (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
On Wed, Oct 25, 2017 at 11:38:09AM +0200, Miklos Szeredi wrote: >On Tue, Oct 24, 2017 at 08:10:49PM +0200, Jakob Unterwurzacher wrote: >> A user running a Haskell program [1] noticed a problem with fuse's >> readdirplus: when it is interrupted by a signal, it skips one >> directory entry. >> >> The problem is most apparent with Haskell as it uses >> SIGVTALRM to interrupt it's own green threads. >> >> A minimal reproducer in C, "ls-count.c", is available [2]. The problem >> has been reproduced against libfuse's "passthrough_fh.c", but also against >> gocryptfs, which uses go-fuse instead of libfuse. This suggest >> that the bug is in kernel-space, which also the opinion of libfuse >> upstream [3]. >> >> What "ls-count.c" does is that it loops over readdir while sending itself >> SIGVTALRM. When the count of directory entries changes, it exits: >> >> $ ./ls-count b >> ls-count: counts do not match: 2 vs 1 >> >> strace against ls-count shows that we get one entry, when we should get >> two ("." and ".."): >> >> getdents(3, /* 1 entries */, 32768) = 24 >> --- SIGVTALRM --- >> rt_sigreturn({mask=[]}) = 24 >> getdents(3, /* 0 entries */, 32768) = 0 >> >> The debug output from go-fuse [4] shows what seems to be happening: >> >> Dispatch 548: READDIRPLUS, NodeId: 1. data: {Fh 3 off 0 sz 4096} >> Serialize 548: READDIRPLUS code: OK value: 320 bytes data >> Dispatch 549: READDIRPLUS, NodeId: 1. data: {Fh 3 off 2 sz 4096} >> Serialize 549: READDIRPLUS code: OK value: >> >> The kernel starts reading the directory from "off 0", where it is >> interrupted, and only returns one entry to userspace. Then it continues >> reading at "off 2". Offset 1 is skipped. >> >> I can reliably reproduce this within 1 second against kernel 4.12.5. > >Thanks for the report. The patch below should fix it. > Hi Miklos, Original reporter here ("Haskell user"). I tested your patch and everything works as expected now. Thanks for the prompt response! - Marios >Thanks, >Miklos >--- > >From: Miklos Szeredi <mszeredi@redhat.com> >Subject: fuse: fix READDIRPLUS skipping an entry > >A user running a Haskell program noticed a problem with fuse's readdirplus: >when it is interrupted by a signal, it skips one directory entry. > >The reason is that fuse erronously updates ctx->pos after a failed >dir_emit(). > >The issue originates from the patch adding readdirplus support. > >Reported-by: Jakob Unterwurzacher <jakobunt@gmail.com> >Signed-off-by: Miklos Szeredi <mszeredi@redhat.com> >Fixes: 0b05b18381ee ("fuse: implement NFS-like readdirplus support") >Cc: <stable@vger.kernel.org> # v3.9 >--- > fs/fuse/dir.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > >--- a/fs/fuse/dir.c >+++ b/fs/fuse/dir.c >@@ -1308,7 +1308,8 @@ static int parse_dirplusfile(char *buf, > */ > over = !dir_emit(ctx, dirent->name, dirent->namelen, > dirent->ino, dirent->type); >- ctx->pos = dirent->off; >+ if (!over) >+ ctx->pos = dirent->off; > } > > buf += reclen;
On Wed, Oct 25, 2017 at 4:28 PM, Marios Titas <redneb@gmx.com> wrote: > Original reporter here ("Haskell user"). I tested your patch and everything > works as expected now. Thanks for the prompt response! Thanks for the report and testing. Thanks, Miklos
--- a/fs/fuse/dir.c +++ b/fs/fuse/dir.c @@ -1308,7 +1308,8 @@ static int parse_dirplusfile(char *buf, */ over = !dir_emit(ctx, dirent->name, dirent->namelen, dirent->ino, dirent->type); - ctx->pos = dirent->off; + if (!over) + ctx->pos = dirent->off; } buf += reclen;