On Fri, Dec 16, 2016 at 04:40:41PM +0100, Michal Hocko wrote:
> Updated patch after Mike noticed a BUG_ON when KM_NOLOCKDEP is used.
> ---
> From 1497e713e11639157aef21cae29052cb3dc7ab44 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@xxxxxxxx>
> Date: Thu, 15 Dec 2016 13:06:43 +0100
> Subject: [PATCH] xfs: introduce and use KM_NOLOCKDEP to silence reclaim
> lockdep false positives
>
> Now that the page allocator offers __GFP_NOLOCKDEP let's introduce
> KM_NOLOCKDEP alias for the xfs allocation APIs. While we are at it
> also change KM_NOFS users introduced by b17cb364dbbb ("xfs: fix missing
> KM_NOFS tags to keep lockdep happy") and use the new flag for them
> instead. There is really no reason to make these allocations contexts
> weaker just because of the lockdep which even might not be enabled
> in most cases.
>
Hi Michal,
I haven't gone back to fully grok b17cb364dbbb ("xfs: fix missing
KM_NOFS tags to keep lockdep happy"), so I'm not really familiar with
the original problem. FWIW, there was another KM_NOFS instance added by
that commit in xlog_cil_prepare_log_vecs() that is now in
xlog_cil_alloc_shadow_bufs(). Perhaps Dave can confirm whether the
original issue still applies..?
Brian
> Changes since v1
> - check for KM_NOLOCKDEP in kmem_flags_convert to not hit sanity BUG_ON
> as per Mike Galbraith
>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> fs/xfs/kmem.h | 6 +++++-
> fs/xfs/libxfs/xfs_da_btree.c | 4 ++--
> fs/xfs/xfs_buf.c | 2 +-
> fs/xfs/xfs_dir2_readdir.c | 2 +-
> 4 files changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/fs/xfs/kmem.h b/fs/xfs/kmem.h
> index 689f746224e7..d5d634ef1f7f 100644
> --- a/fs/xfs/kmem.h
> +++ b/fs/xfs/kmem.h
> @@ -33,6 +33,7 @@ typedef unsigned __bitwise xfs_km_flags_t;
> #define KM_NOFS ((__force xfs_km_flags_t)0x0004u)
> #define KM_MAYFAIL ((__force xfs_km_flags_t)0x0008u)
> #define KM_ZERO ((__force xfs_km_flags_t)0x0010u)
> +#define KM_NOLOCKDEP ((__force xfs_km_flags_t)0x0020u)
>
> /*
> * We use a special process flag to avoid recursive callbacks into
> @@ -44,7 +45,7 @@ kmem_flags_convert(xfs_km_flags_t flags)
> {
> gfp_t lflags;
>
> - BUG_ON(flags & ~(KM_SLEEP|KM_NOSLEEP|KM_NOFS|KM_MAYFAIL|KM_ZERO));
> + BUG_ON(flags & ~(KM_SLEEP|KM_NOSLEEP|KM_NOFS|KM_MAYFAIL|KM_ZERO|KM_NOLOCKDEP));
>
> if (flags & KM_NOSLEEP) {
> lflags = GFP_ATOMIC | __GFP_NOWARN;
> @@ -57,6 +58,9 @@ kmem_flags_convert(xfs_km_flags_t flags)
> if (flags & KM_ZERO)
> lflags |= __GFP_ZERO;
>
> + if (flags & KM_NOLOCKDEP)
> + lflags |= __GFP_NOLOCKDEP;
> +
> return lflags;
> }
>
> diff --git a/fs/xfs/libxfs/xfs_da_btree.c b/fs/xfs/libxfs/xfs_da_btree.c
> index f2dc1a950c85..b8b5f6914863 100644
> --- a/fs/xfs/libxfs/xfs_da_btree.c
> +++ b/fs/xfs/libxfs/xfs_da_btree.c
> @@ -2429,7 +2429,7 @@ xfs_buf_map_from_irec(
>
> if (nirecs > 1) {
> map = kmem_zalloc(nirecs * sizeof(struct xfs_buf_map),
> - KM_SLEEP | KM_NOFS);
> + KM_SLEEP | KM_NOLOCKDEP);
> if (!map)
> return -ENOMEM;
> *mapp = map;
> @@ -2488,7 +2488,7 @@ xfs_dabuf_map(
> */
> if (nfsb != 1)
> irecs = kmem_zalloc(sizeof(irec) * nfsb,
> - KM_SLEEP | KM_NOFS);
> + KM_SLEEP | KM_NOLOCKDEP);
>
> nirecs = nfsb;
> error = xfs_bmapi_read(dp, (xfs_fileoff_t)bno, nfsb, irecs,
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 7f0a01f7b592..f31ae592dcae 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1785,7 +1785,7 @@ xfs_alloc_buftarg(
> {
> xfs_buftarg_t *btp;
>
> - btp = kmem_zalloc(sizeof(*btp), KM_SLEEP | KM_NOFS);
> + btp = kmem_zalloc(sizeof(*btp), KM_SLEEP | KM_NOLOCKDEP);
>
> btp->bt_mount = mp;
> btp->bt_dev = bdev->bd_dev;
> diff --git a/fs/xfs/xfs_dir2_readdir.c b/fs/xfs/xfs_dir2_readdir.c
> index 003a99b83bd8..033ed65d7ce6 100644
> --- a/fs/xfs/xfs_dir2_readdir.c
> +++ b/fs/xfs/xfs_dir2_readdir.c
> @@ -503,7 +503,7 @@ xfs_dir2_leaf_getdents(
> length = howmany(bufsize + geo->blksize, (1 << geo->fsblog));
> map_info = kmem_zalloc(offsetof(struct xfs_dir2_leaf_map_info, map) +
> (length * sizeof(struct xfs_bmbt_irec)),
> - KM_SLEEP | KM_NOFS);
> + KM_SLEEP | KM_NOLOCKDEP);
> map_info->map_size = length;
>
> /*
> --
> 2.10.2
>
> --
> Michal Hocko
> SUSE Labs
> --
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