Good catch! And thanks for the detailed explanation. Applying for 5.2 and stable.
On Wed, Jul 03, 2019 at 02:54:43PM +0200, Paul Menzel wrote: > Date: Wed, 3 Jul 2019 13:28:15 +0200 > > Since commit 10a68cdf10 (nfsd: fix performance-limiting session > calculation) (Linux 5.1-rc1 and 4.19.31), shares from NFS servers with > 1 TB of memory cannot be mounted anymore. The mount just hangs on the > client. > > The gist of commit 10a68cdf10 is the change below. > > -avail = clamp_t(int, avail, slotsize, avail/3); > +avail = clamp_t(int, avail, slotsize, total_avail/3); > > Here are the macros. > > #define min_t(type, x, y) __careful_cmp((type)(x), (type)(y), <) > #define clamp_t(type, val, lo, hi) min_t(type, max_t(type, val, lo), hi) > > `total_avail` is 8,434,659,328 on the 1 TB machine. `clamp_t()` casts > the values to `int`, which for 32-bit integers can only hold values > −2,147,483,648 (−2^31) through 2,147,483,647 (2^31 − 1). > > `avail` (in the function signature) is just 65536, so that no overflow > was happening. Before the commit the assignment would result in 21845, > and `num = 4`. > > When using `total_avail`, it is causing the assignment to be > 18446744072226137429 (printed as %lu), and `num` is then 4164608182. > > My next guess is, that `nfsd_drc_mem_used` is then exceeded, and the > server thinks there is no memory available any more for this client. > > Updating the arguments of `clamp_t()` and `min_t()` to `unsigned long` > fixes the issue. > > Now, `avail = 65536` (before commit 10a68cdf10 `avail = 21845`), but > `num = 4` remains the same. > > Fixes: 10a68cdf10 (nfsd: fix performance-limiting session calculation) > Cc: sta...@vger.kernel.org > Signed-off-by: Paul Menzel <pmen...@molgen.mpg.de> > --- > > 1. No, idea if `min_t()` arguments also need updating. > 2. Instead of `unsigned long`, should `size_t` be used? > > fs/nfsd/nfs4state.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > index 618e66078ee5..1a0cdeb3b875 100644 > --- a/fs/nfsd/nfs4state.c > +++ b/fs/nfsd/nfs4state.c > @@ -1563,7 +1563,7 @@ static u32 nfsd4_get_drc_mem(struct nfsd4_channel_attrs > *ca) > * Never use more than a third of the remaining memory, > * unless it's the only way to give this client a slot: > */ > - avail = clamp_t(int, avail, slotsize, total_avail/3); > + avail = clamp_t(unsigned long, avail, slotsize, total_avail/3); > num = min_t(int, num, avail / slotsize); > nfsd_drc_mem_used += num * slotsize; > spin_unlock(&nfsd_drc_lock); > -- > 2.22.0 >
