From 8ef123fe02ca0923b01b57bdf639800a23a2faa8 Mon Sep 17 00:00:00 2001 From: Ritesh Harjani Date: Wed, 20 May 2020 12:10:35 +0530 Subject: [PATCH] ext4: mballoc: refactor ext4_mb_good_group() ext4_mb_good_group() definition was changed some time back and now it even initializes the buddy cache (via ext4_mb_init_group()), if in case the EXT4_MB_GRP_NEED_INIT() is true for a group. Note that ext4_mb_init_group() could sleep and so should not be called under a spinlock held. This is fine as of now because ext4_mb_good_group() is called before loading the buddy bitmap without ext4_lock_group() held and again called after loading the bitmap, only this time with ext4_lock_group() held. But still this whole thing is confusing. So this patch refactors out ext4_mb_good_group_nolock() which should be called when without holding ext4_lock_group(). Also in further patches we hold the spinlock (ext4_lock_group()) while doing any calculations which involves grp->bb_free or grp->bb_fragments. Signed-off-by: Ritesh Harjani Link: https://lore.kernel.org/r/d9f7d031a5fbe1c943fae6bf1ff5cdf0604ae722.1589955723.git.riteshh@linux.ibm.com Signed-off-by: Theodore Ts'o --- fs/ext4/mballoc.c | 78 +++++++++++++++++++++++++++++++++++-------------------- 1 file changed, 50 insertions(+), 28 deletions(-) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 754ff9f..c9297c8 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -2106,15 +2106,14 @@ void ext4_mb_scan_aligned(struct ext4_allocation_context *ac, } /* - * This is now called BEFORE we load the buddy bitmap. + * This is also called BEFORE we load the buddy bitmap. * Returns either 1 or 0 indicating that the group is either suitable - * for the allocation or not. In addition it can also return negative - * error code when something goes wrong. + * for the allocation or not. */ -static int ext4_mb_good_group(struct ext4_allocation_context *ac, +static bool ext4_mb_good_group(struct ext4_allocation_context *ac, ext4_group_t group, int cr) { - unsigned free, fragments; + ext4_grpblk_t free, fragments; int flex_size = ext4_flex_bg_size(EXT4_SB(ac->ac_sb)); struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group); @@ -2122,23 +2121,16 @@ static int ext4_mb_good_group(struct ext4_allocation_context *ac, free = grp->bb_free; if (free == 0) - return 0; + return false; if (cr <= 2 && free < ac->ac_g_ex.fe_len) - return 0; + return false; if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp))) - return 0; - - /* We only do this if the grp has never been initialized */ - if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) { - int ret = ext4_mb_init_group(ac->ac_sb, group, GFP_NOFS); - if (ret) - return ret; - } + return false; fragments = grp->bb_fragments; if (fragments == 0) - return 0; + return false; switch (cr) { case 0: @@ -2148,31 +2140,63 @@ static int ext4_mb_good_group(struct ext4_allocation_context *ac, if ((ac->ac_flags & EXT4_MB_HINT_DATA) && (flex_size >= EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME) && ((group % flex_size) == 0)) - return 0; + return false; if ((ac->ac_2order > ac->ac_sb->s_blocksize_bits+1) || (free / fragments) >= ac->ac_g_ex.fe_len) - return 1; + return true; if (grp->bb_largest_free_order < ac->ac_2order) - return 0; + return false; - return 1; + return true; case 1: if ((free / fragments) >= ac->ac_g_ex.fe_len) - return 1; + return true; break; case 2: if (free >= ac->ac_g_ex.fe_len) - return 1; + return true; break; case 3: - return 1; + return true; default: BUG(); } - return 0; + return false; +} + +/* + * This could return negative error code if something goes wrong + * during ext4_mb_init_group(). This should not be called with + * ext4_lock_group() held. + */ +static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac, + ext4_group_t group, int cr) +{ + struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group); + ext4_grpblk_t free; + int ret = 0; + + free = grp->bb_free; + if (free == 0) + goto out; + if (cr <= 2 && free < ac->ac_g_ex.fe_len) + goto out; + if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp))) + goto out; + + /* We only do this if the grp has never been initialized */ + if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) { + ret = ext4_mb_init_group(ac->ac_sb, group, GFP_NOFS); + if (ret) + return ret; + } + + ret = ext4_mb_good_group(ac, group, cr); +out: + return ret; } static noinline_for_stack int @@ -2260,7 +2284,7 @@ repeat: group = 0; /* This now checks without needing the buddy page */ - ret = ext4_mb_good_group(ac, group, cr); + ret = ext4_mb_good_group_nolock(ac, group, cr); if (ret <= 0) { if (!first_err) first_err = ret; @@ -2278,11 +2302,9 @@ repeat: * block group */ ret = ext4_mb_good_group(ac, group, cr); - if (ret <= 0) { + if (ret == 0) { ext4_unlock_group(sb, group); ext4_mb_unload_buddy(&e4b); - if (!first_err) - first_err = ret; continue; } -- 2.7.4