Messages in this thread Patch in this message | | | Subject | [PATCH] nfsd: Fix overflow causing non-working mounts on 1 TB machines | From | Paul Menzel <> | Date | Wed, 3 Jul 2019 14:54:43 +0200 |
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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: stable@vger.kernel.org Signed-off-by: Paul Menzel <pmenzel@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 [unhandled content-type:application/pkcs7-signature] | |