linux-kernel - [PATCH 4.4 92/93] mm: slub: add missing TID bump in kmem_cache_alloc

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Message-Id: <20200319123953.547695284@linuxfoundation.org>
Date:   Thu, 19 Mar 2020 14:00:36 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jann Horn <jannh@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.4 92/93] mm: slub: add missing TID bump in kmem_cache_alloc_bulk()

From: Jann Horn <jannh@...gle.com>

commit fd4d9c7d0c71866ec0c2825189ebd2ce35bd95b8 upstream.

When kmem_cache_alloc_bulk() attempts to allocate N objects from a percpu
freelist of length M, and N > M > 0, it will first remove the M elements
from the percpu freelist, then call ___slab_alloc() to allocate the next
element and repopulate the percpu freelist. ___slab_alloc() can re-enable
IRQs via allocate_slab(), so the TID must be bumped before ___slab_alloc()
to properly commit the freelist head change.

Fix it by unconditionally bumping c->tid when entering the slowpath.

Cc: stable@...r.kernel.org
Fixes: ebe909e0fdb3 ("slub: improve bulk alloc strategy")
Signed-off-by: Jann Horn <jannh@...gle.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/slub.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2932,6 +2932,15 @@ int kmem_cache_alloc_bulk(struct kmem_ca
 
 		if (unlikely(!object)) {
 			/*
+			 * We may have removed an object from c->freelist using
+			 * the fastpath in the previous iteration; in that case,
+			 * c->tid has not been bumped yet.
+			 * Since ___slab_alloc() may reenable interrupts while
+			 * allocating memory, we should bump c->tid now.
+			 */
+			c->tid = next_tid(c->tid);
+
+			/*
 			 * Invoking slow path likely have side-effect
 			 * of re-populating per CPU c->freelist
 			 */